Search Results

Search found 30941 results on 1238 pages for 'background process'.

Page 429/1238 | < Previous Page | 425 426 427 428 429 430 431 432 433 434 435 436  | Next Page >

  • OFM 11g: Implementing OAM SSO with Forms

    - by olaf.heimburger
    There is some confusion about the integration of OFM 11g Forms with Oracle Access Manager 11g (OAM). Some say this does not work, some say it works, but.... Actually, having implemented it many times I belong to the later group. Here is how. Caveat Before you start installing anything, take a step back and consider your current implementation and what you really need and want to achieve. The current integration of Forms 11g with OAM 11g does not support self-service account creation and password resets from the Forms application. If you really need this, you must use the existing Oracle AS 10.1.4.3 infrastructure. On the other hand, if your user population is pretty stable, you can enjoy the latest Forms 11g with OAM 11g. Assumptions The whole process should be done in one day. I assume that all domains and instances are started during setup, if you need to restart them on demand or purpose, be sure to have proper start/stop scripts, I don't mention them. Preparation It goes without saying, that you always should do a proper backup before you change anything on your production environment. With proper backup, I also mean a tested and verified restore process. If you dared to test it before, do it now. It pays off. Requirements For OAM 11g to work properly you need a LDAP repository. For the integration of Forms 11g you need an Oracle Internet Directory (OID) configured with the Oracle AS SSO LDAP extensions. For better support I usually give the latest version a try, in this case OID 11g is a good choice.During the Installation and Integration steps we use an upgrade wizard that needs the old OID configuration on the same host but in a different ORACLE_HOME. Installation vs Configuration With OFM 11g Oracle introduced a clear separation between Installation of the binaries (the software) and the Configuration of the instances (the runtime). This is really great as you can install all the software and create new instances when needed. In the following we adhere to this scheme and install the software first and then configure the instances later. Installation Steps The Oracle documentation contains all the necessary steps for the installation of all pieces of software. But some hints help to avoid traps and pitfalls. Step 1 The Database Start the installation with the database. It is quite obvious but we need an Oracle database for all the other steps. If you have one at hand, fine. If not, just install at least a Oracle 10.2.0.4 version. This database can be on a different host. Step 2 The Repository Creation Utility The next step should be to run the Repository Creation Utility (RCU). This is a client application that just needs to connect to your database. It can be run on any host that can reach the database and is a Windows or Linux 32-bit machine. When you run it, be sure to install the OID schema and the OAM schema. If you miss one of these, you can run the RCU again to install the missing schema. Step 3 The Foundation With OFM 11g Oracle started to use WebLogic Server 11g (WLS) as its foundation for all OFM 11g installation. We therefore install it first. Depending on your operating system, it might be possible, that no native installer is available. My approach to this dilemma is to use the WLS Generic Installer for all my installations. It does not include a JDK either but if you have both for your platform you are ready to go. Step 3a The JDK To make things interesting, Oracle currently has two JDKs in its portfolio. The Sun JDK and the JRockit JDK. Both are available for a number of platforms. If you are lucky and both are available for your platform, install both in a separate directory (and not one of your ORACLE_HOMEs) each, You can use the later as you like. Step 3b Install WLS for OID and OAM With the JDK installed, we start the generic installer with java -jar wls_generic.jar.STOP! Before you do this, check the version first. It should be 1.6.0_18 or later and not the GCC one (Some Linux distros have it installed by default). To verify the version, issue a java -version command and make sure that the output does not contain the text gcj and the version matches. If this does not work, use an absolute path like /opt/java/jdk1.6.0_23/bin/java to start the installer. The installer allows you to specify a path to install the software into, say /opt/oracle/iam/11.1.1.3 for the OID and OAM installation. We will call this IAM_HOME. Step 4 Install OID Now we are ready to install OID. Start the OID installer (in the Disk1 directory) and just select the installation only step. This will install the software only and does not configure the instance. Use the IAM_HOME as the target directory. Step 5 Install SOA Suite The IAM 11g Suite uses the BPEL component of the SOA Suite 11g for its workflows. This is a pretty closed environment and not to be used for SCA Composites. We install the SOA Suite in $IAM_HOME/soa. The installer only installs the binaries. Configuration will be done later. Step 6 Install OAM Once the installation of OID and SOA is done, we are ready to install the OAM software in the same IAM_HOME. Make sure to install the OAM binaries in a directory different from the one you used during the OID and SOA installation. As before, we only install the software, the instance will be created later. Step 7 Backup the Installation At this point, I normally do a backup (or snapshot in a virtual image) of the installation. Good when you need to go back to this point. Step 8 Configure OID The software is installed and now we need instances to run it. This process is called configuration. For OID use the config.sh found in $IAM_HOME/oid/bin to start the configuration wizard. Normally this runs smoothly. If you encounter some issues check the Oracle Support site for help. This configuration will also start the OID instance. Step 9 Install the Oracle AS SSO Schema Before we install the Forms software we need to install the Oracle AS SSO Schema into the database and OID. This is a rather dangerous procedure, but fully documented in the IAM Installation Guide, Chapter 10. You should finish this in one go, do not reboot your host during the whole procedure. As a precaution, you should make a backup of the OID instance before you start the procedure. Once the backup is ready, read the chapter, including every note, carefully. You can avoid a number of issues by following all the steps and will succeed with a working solution. Step 10 Configure OAM Reached this step? Great. You are ready to create an OAM instance. Use the $IAM_HOME/iam/common/binconfig.sh for this. This will open the WLS Domain Creation Wizard and asks for the libraries to be installed. You should at least select the OAM with Database repository item. The configuration will also start the OAM instance. Step 11 Install WLS for Forms 11g It is quite tempting to install everything in one ORACLE_HOME. Unfortunately this does not work for all OFM packages. Therefore we do another WLS installation in another ORACLE_HOME. The same considerations as in step 3b apply. We call this one FORMS_HOME. Step 12 Install Forms In the FORMS_HOME we now install the binaries for the Forms 11g software. Again, this is a install only step. Configuration starts with the next step. Step 13 Configure Forms To configure Forms 11g we start the Configuration Wizard (config.sh) in FORMS_HOME/bin. This wizard should create a new WebLogic Domain and an OHS instance! Do not extend existing domains or instances! Forms should run in its own instances! When all information is supplied, the wizard will create the domain and instance and starts them automatically.Step 14 Setup your Forms SSO EnvironmentOnce you have implemented and tested your Forms 11g instance, you can configured it for SSO. Yes, this requires the old Oracle AS SSO solution, OIDDAS for creating and assigning users and SSO to setup your partner applications. In this step you should consider to create every user necessary for use within the environment. When done, do not forget to test it. Step 15 Migrate the SSO Repository Since the final goal is to get rid of the old SSO implementation we need to migrate the old SSO repository into the new OID structure. Additionally, this step will also migrate all partner application configurations into OAM 11g. Quite convenient. To do this step, you have to start the upgrade agent (ua or ua.bat or ua.cmd) on the operating system level in $IAM_HOME/bin. Once finished, this wizard will create new osso.conf files for each partner application in $IAM_HOME/upgrade/temp/oam/.Note: At the time of this writing, this step only works if everything is on the same host (ie. OID, OAM, etc.). This restriction might be lifted in later releases. Step 16 Change your OHS sso.conf and shut down OC4J_SECURITY In Step 14 we verified that SSO for our Forms environment works fine. Now, we are shutting the old system done and reconfigure the OHS that acts as the Forms entry point. First we go to the OHS configuration directory and rename the old osso.conf  to osso.conf.10g. Now we change the moduleconf/mod_osso.conf  to point to the new osso.conf file. Copy the new osso.conf  file from $IAM_HOME/upgrade/temp/oam/ to the OHS configuration directory. Restart OHS, test forms by using the same forms links. OAM should now kick in and show the login dialog to ask for your user credentials.Done. Now your Forms environment is successfully integrated with OAM 11g.Enjoy. What's Next? This rather lengthy setup is just the foundation for your growing environment of OAM 11g protections. In the next entry we will show that Forms 11g and ADF Faces 11g can use the same OAM installation and provide real single sign-on. References Nearly everything is documented. Use the documentation! Oracle® Fusion Middleware Installation Guide for Oracle Identity Management 11gR1 Oracle® Fusion Middleware Installation Guide for Oracle Identity Management 11gR1, Chapter 11-14 Oracle® Fusion Middleware Administrator's Guide for Oracle Access Manager 11gR1, Appendix B Oracle® Fusion Middleware Upgrade Guide for Oracle Identity Management 11gR1, Chapter 10   

    Read the article

  • Application for taking pretty screenshots (like OS X does)

    - by Oli
    I've been building a website for a guy who uses Mac OS X and occasionally he sends me screenshots of bugs. They come out looking like this: This is fairly typical of Mac screenshots. You get the window decorations, the shadow from the window and a white or transparent background (not the desktop wallpaper -- I've checked). Compare this to an Ubuntu window-shot (Alt+Print screen): It's impossible to keep a straight face and say the Ubuntu one anywhere near as elegant. My question is: Is there an application that can do this in Ubuntu? Edit: Follow up: Is there an application that can do this in one move? Shutter is pretty good but running the plugin for every screenshot is pretty tiresome as it doesn't seem to remember my preference (I want south-shadow and that requires selecting south, then clicking refresh, then save) and it's more clicks than I'd like. Is there a simple way of telling shutter I want south-shadow for all screenshots (except entire desktop and area-selection)?

    Read the article

  • Google I/O 2010 - Creating positive user experiences

    Google I/O 2010 - Creating positive user experiences Google I/O 2010 - Beyond design: Creating positive user experiences Tech Talks John Zeratsky, Matt Shobe Good user experience isn't just about good design. Learn how to create a positive user experience by being fast, open, engaged, surprising, polite, and, well... being yourself. Chock full of examples from the web and beyond, this talk is a practical introduction for developers who are passionate about user experience but may not have a background in design. For all I/O 2010 sessions, please go to code.google.com From: GoogleDevelopers Views: 185 6 ratings Time: 52:11 More in Science & Technology

    Read the article

  • Any Good Cocos2d Pause Menu Library

    - by Mahbubur R Aaman
    Background : From http://code.google.com/p/cocos2d-iphone/issues/detail?id=173 Scenes/Nodes doesn't support the CocosNodeOpacity protocol. From http://playsnackgames.com/blog/2011/09/cocos2d-tutorial-creating-a-reusable-pause-layer/ Cocos2d offers a simple method to pause and resume itself, but these methods stop the CCDirector (the class that manages most aspects of a Cocos2d’s app lifetime) from running actions and lower the fps to 5 to conserve battery life. Related issues http://www.cocos2d-iphone.org/forum/topic/4368 http://www.cocos2d-iphone.org/forum/topic/151 http://stackoverflow.com/questions/5852354/cocos2d-engine-pause-resume http://stackoverflow.com/questions/11878450/how-to-pause-a-layer-in-cocos2d-2-0 Question : Is there any Good Cocos2d Pause Menu Library solving these tricky issues? This will save many hours of Game Developer's life.

    Read the article

  • Need help choosing between Grails and Yii Framework

    - by user530207
    I recently started on developing in PHP with the Yii Framework. I recently came across the Grails Framework and I'm pretty impressed by the sites they make, bigger companies seem to use Grails for their web development. When looking at yii, not many big companies are using it. I'm just starting out with the Yii framework and I don't want to turn back halfway when in the middle of learning Yii, so I hope someone can give me some comparison about the 2 in terms of power. Does Grails make things much easier and benefit me in the long run? I only have C++ background for now. It boils down to this. I want a powerful framework which will serve me for a very long time and by looking at the number of big companies using Grails, I feel discouraged to take the Yii path. Thank you! Some sites by Grails: http://video.sky.com/ http://espn.go.com/ http://www.atlassian.com/ http://www.linkedin.com/

    Read the article

  • Bing Desktop Automatically Downloads Bing Wallpapers to Your Computer

    - by Jason Fitzpatrick
    Windows 7: Bing Desktop is a new and lightweight offering from Microsoft that automatically swaps your desktop background every day and offers quick access to the Bing search engine. In addition to downloading the Bing wallpaper, Bing Desktop also includes a small search box that allows you to search Bing from your desktop–although most users will likely grab the app simply to get the daily wallpaper update. Hit up the link below to download a copy. Bing Desktop is free, Windows 7 only. Bing Desktop [via Quick Online Tips] How to Stress Test the Hard Drives in Your PC or Server How To Customize Your Android Lock Screen with WidgetLocker The Best Free Portable Apps for Your Flash Drive Toolkit

    Read the article

  • How to Fix the “Firefox Is Already Running” Error

    - by Chris Hoffman
    The “Firefox is already running, but is not responding” error has haunted Firefox users for years. You don’t have to restart your computer when you see this error – you can usually fix it with a quick trip to the Task Manager. This error occurs when Firefox is closed but is still running in the background. Firefox is either in the process of closing or is frozen and hasn’t quit properly. In rare situations, there may be a problem with your profile. Secure Yourself by Using Two-Step Verification on These 16 Web Services How to Fix a Stuck Pixel on an LCD Monitor How to Factory Reset Your Android Phone or Tablet When It Won’t Boot

    Read the article

  • Pure virtual or abstract, what's in a name?

    - by Steven Jeuris
    While discussing a question about virtual functions on Stack Overflow, I wondered whether there was any official naming for pure (abstract) and non-pure virtual functions. I always relied on wikipedia for my information, which states that pure and non-pure virtual functions are the general term. Unfortunately, the article doesn't back it up with a origin or references. To quote Jon Skeet's answer to my reply that pure and non-pure are the general term used: @Steven: Hmm... possibly, but I've only ever seen it in the context of C++ before. I suspect anyone talking about them is likely to have a C++ background :) Did the terms originate from C++, or were they first defined or implemented in a earlier language, and are they the 'official' scientific terms?

    Read the article

  • SharePoint 2010 Hosting :: How to Customize SharePoint 2010 Global Navigation

    - by mbridge
    Requirements - SharePoint Foundation or SharePoint Server 2010 site - SharePoint Designer 2010 Steps 1. The first step in my process was to download from codeplex a starter masterpage http://startermasterpages.codeplex.com/ . 2. Once you downloaded the starter master page, open up your SharePoint site in SharePoint Designer 2010 and on the left in the “Site Objects “ area click on the folder “All Files” and drill down to catalogs >> masterpages . Once you are in the Masterpage folder copy and paste the _starter.master into this folder. 3. The first step in the customization process is to create your custom style sheet. To create your custom style sheet, click on the “all Files” folder and click on “Style Library.” Right click in the style library section and choose Style sheet. Once the style sheet is created, rename it style.css. Now open the style sheet you created in SharePoint Designer. 4. In this next step you will copy and paste the SharePoint core styles for the global navigation into your custom style sheet. Copy and paste the css below into the style sheet and save file .s4-tn{ padding:0px; margin:0px; } .s4-tn ul.static{ white-space:nowrap; } .s4-tn li.static > .menu-item{ /* [ReplaceColor(themeColor:"Dark2")] */ color:#3b4f65; white-space:nowrap; border:1px solid transparent; padding:4px 10px; display:inline-block; height:15px; vertical-align:middle; } .s4-tn ul.dynamic{ /* [ReplaceColor(themeColor:"Light2")] */ background-color:white; /* [ReplaceColor(themeColor:"Dark2-Lighter")] */ border:1px solid #D9D9D9; } .s4-tn li.dynamic > .menu-item{ display:block; padding:3px 10px; white-space:nowrap; font-weight:normal; } .s4-tn li.dynamic > a:hover{ font-weight:normal; /* [ReplaceColor(themeColor:"Light2-Lighter")] */ background-color:#D9D9D9; } .s4-tn li.static > a:hover { /* [ReplaceColor(themeColor:"Accent1")] */ color:#44aff6; text-decoration:underline; } 5. Once you created the style sheet, go back to the masterpage folder and open the _starter.master file and in the Customization category click edit file. 6. Next, when the edit file opens make sure you view it in split view. Now you are going to search for the reference to our custom masterpage in the code. Make sure you are scrolled to the top in the code section and press “ctrl f” on the key board. This will pop up the find and replace tool. In the” find what field”, copy and paste and then click find next. 7. Now, in the code replace You have now referenced your custom style sheet in your masterpage. 8. The next step is to locate your Global Navigation control, make sure you are scrolled to the top in the code section and press “ctrl f” on the key board. This will pop up the find and replace tool. In the” find what field”, copy and paste ID="TopNavigationMenuV4” and then click find next. Once you find ID="TopNavigationMenuV4” , you should see the following block of code which is the global navigation control: ID="TopNavigationMenuV4" Runat="server" EnableViewState="false" DataSourceID="topSiteMap" AccessKey="" UseSimpleRendering="true" UseSeparateCss="false" Orientation="Horizontal" StaticDisplayLevels="1" MaximumDynamicDisplayLevels="1" SkipLinkText="" CssClass="s4-tn" 9. In the global navigation code above you should see CssClass="s4-tn" . As an additional step you can replace "s4-tn" your own custom name like CssClass="MyNav" . If you can the name of the CSS class make sure you update your custom style sheet with the new name, example below: .MyNav{ padding:0px; margin:0px; } .MyNav ul.static{ white-space:nowrap; } 10. At this point you are ready to brand your global navigation. The next step is to modify your style.css with your customizations to the default SharePoint styles. Have fun styling and make sure you save your work often. Hope it helps!!

    Read the article

  • Why does Clojure neglect the uniform access principle?

    - by Alexey
    My background is Ruby, C#, JavaScript and Java. And now I'm learning Clojure. What makes me feel uncomfortable about the later is that idiomatic Clojure seems to neglect the Uniform access principle (wiki, c2) and thus to a certain degree encapsulation as well by suggesting to use maps instead of some sort of "structures" or "classes". It feels like step back. So a couple of questions, if anyone informed: Which other design decisions/concerns it conflicted with and why it was considered less important? Did you have the same concern as well and how it end up when you switched from a language supporting UAP by default (Ruby, Eiffel, Python, C#) to Clojure?

    Read the article

  • SQL SERVER – Weekly Series – Memory Lane – #038

    - by Pinal Dave
    Here is the list of selected articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2007 CASE Statement in ORDER BY Clause – ORDER BY using Variable This article is as per request from the Application Development Team Leader of my company. His team encountered code where the application was preparing string for ORDER BY clause of the SELECT statement. Application was passing this string as variable to Stored Procedure (SP) and SP was using EXEC to execute the SQL string. This is not good for performance as Stored Procedure has to recompile every time due to EXEC. sp_executesql can do the same task but still not the best performance. SSMS – View/Send Query Results to Text/Grid/Files Results to Text – CTRL + T Results to Grid – CTRL + D Results to File – CTRL + SHIFT + F 2008 Introduction to SPARSE Columns Part 2 I wrote about Introduction to SPARSE Columns Part 1. Let us understand the concept of the SPARSE column in more detail. I suggest you read the first part before continuing reading this article. All SPARSE columns are stored as one XML column in the database. Let us see some of the advantage and disadvantage of SPARSE column. Deferred Name Resolution How come when table name is incorrect SP can be created successfully but when an incorrect column is used SP cannot be created? 2009 Backup Timeline and Understanding of Database Restore Process in Full Recovery Model In general, databases backup in full recovery mode is taken in three different kinds of database files. Full Database Backup Differential Database Backup Log Backup Restore Sequence and Understanding NORECOVERY and RECOVERY While doing RESTORE Operation if you restoring database files, always use NORECOVER option as that will keep the database in a state where more backup file are restored. This will also keep database offline also to prevent any changes, which can create itegrity issues. Once all backup file is restored run RESTORE command with a RECOVERY option to get database online and operational. Four Different Ways to Find Recovery Model for Database Perhaps, the best thing about technical domain is that most of the things can be executed in more than one ways. It is always useful to know about the various methods of performing a single task. Two Methods to Retrieve List of Primary Keys and Foreign Keys of Database When Information Schema is used, we will not be able to discern between primary key and foreign key; we will have both the keys together. In the case of sys schema, we can query the data in our preferred way and can join this table to another table, which can retrieve additional data from the same. Get Last Running Query Based on SPID PID is returns sessions ID of the current user process. The acronym SPID comes from the name of its earlier version, Server Process ID. 2010 SELECT * FROM dual – Dual Equivalent Dual is a table that is created by Oracle together with data dictionary. It consists of exactly one column named “dummy”, and one record. The value of that record is X. You can check the content of the DUAL table using the following syntax. SELECT * FROM dual Identifying Statistics Used by Query Someone asked this question in my training class of query optimization and performance tuning.  “Can I know which statistics were used by my query?” 2011 SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 14 of 31 What are the basic functions for master, msdb, model, tempdb and resource databases? What is the Maximum Number of Index per Table? Explain Few of the New Features of SQL Server 2008 Management Studio Explain IntelliSense for Query Editing Explain MultiServer Query Explain Query Editor Regions Explain Object Explorer Enhancements Explain Activity Monitors SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 15 of 31 What is Service Broker? Where are SQL server Usernames and Passwords Stored in the SQL server? What is Policy Management? What is Database Mirroring? What are Sparse Columns? What does TOP Operator Do? What is CTE? What is MERGE Statement? What is Filtered Index? Which are the New Data Types Introduced in SQL SERVER 2008? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 16 of 31 What are the Advantages of Using CTE? How can we Rewrite Sub-Queries into Simple Select Statements or with Joins? What is CLR? What are Synonyms? What is LINQ? What are Isolation Levels? What is Use of EXCEPT Clause? What is XPath? What is NOLOCK? What is the Difference between Update Lock and Exclusive Lock? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 17 of 31 How will you Handle Error in SQL SERVER 2008? What is RAISEERROR? What is RAISEERROR? How to Rebuild the Master Database? What is the XML Datatype? What is Data Compression? What is Use of DBCC Commands? How to Copy the Tables, Schema and Views from one SQL Server to Another? How to Find Tables without Indexes? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 18 of 31 How to Copy Data from One Table to Another Table? What is Catalog Views? What is PIVOT and UNPIVOT? What is a Filestream? What is SQLCMD? What do you mean by TABLESAMPLE? What is ROW_NUMBER()? What are Ranking Functions? What is Change Data Capture (CDC) in SQL Server 2008? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 19 of 31 How can I Track the Changes or Identify the Latest Insert-Update-Delete from a Table? What is the CPU Pressure? How can I Get Data from a Database on Another Server? What is the Bookmark Lookup and RID Lookup? What is Difference between ROLLBACK IMMEDIATE and WITH NO_WAIT during ALTER DATABASE? What is Difference between GETDATE and SYSDATETIME in SQL Server 2008? How can I Check that whether Automatic Statistic Update is Enabled or not? How to Find Index Size for Each Index on Table? What is the Difference between Seek Predicate and Predicate? What are Basics of Policy Management? What are the Advantages of Policy Management? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 20 of 31 What are Policy Management Terms? What is the ‘FILLFACTOR’? Where in MS SQL Server is ’100’ equal to ‘0’? What are Points to Remember while Using the FILLFACTOR Argument? What is a ROLLUP Clause? What are Various Limitations of the Views? What is a Covered index? When I Delete any Data from a Table, does the SQL Server reduce the size of that table? What are Wait Types? How to Stop Log File Growing too Big? If any Stored Procedure is Encrypted, then can we see its definition in Activity Monitor? 2012 Example of Width Sensitive and Width Insensitive Collation Width Sensitive Collation: A single-byte character (half-width) represented as single-byte and the same character represented as a double-byte character (full-width) are when compared are not equal the collation is width sensitive. In this example we have one table with two columns. One column has a collation of width sensitive and the second column has a collation of width insensitive. Find Column Used in Stored Procedure – Search Stored Procedure for Column Name Very interesting conversation about how to find column used in a stored procedure. There are two different characters in the story and both are having a conversation about how to find column in the stored procedure. Here are two part story Part 1 | Part 2 SQL SERVER – 2012 Functions – FORMAT() and CONCAT() – An Interesting Usage Generate Script for Schema and Data – SQL in Sixty Seconds #021 – Video In simple words, in many cases the database move from one place to another place. It is not always possible to back up and restore databases. There are possibilities when only part of the database (with schema and data) has to be moved. In this video we learn that we can easily generate script for schema for data and move from one server to another one. INFORMATION_SCHEMA.COLUMNS and Value Character Maximum Length -1 I often see the value -1 in the CHARACTER_MAXIMUM_LENGTH column of INFORMATION_SCHEMA.COLUMNS table. I understand that the length of any column can be between 0 to large number but I do not get it when I see value in negative (i.e. -1). Any insight on this subject? Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

    Read the article

  • Applicability of the Joel Test to web development companies

    - by dreftymac
    QUESTION: How can you re-write the questions of the Joel test to apply to web developers? 1. Do you use source control? (source control for all aspects of your app, including configuration, database and user-based settings?) 2. Can you make a build in one step? (can you deploy a site from staging to prod in 1 step?) ... 10. Do you have testers? (how do you test AJAX and CSS?) BACKGROUND: This is for people who work in a shop that does some web development but also uses some off-the-shelf tools like Drupal and Wordpress, but doing custom development on top of that. RELATED LINKS: http://www.joelonsoftware.com/articles/fog0000000043.html What do you think about the Joel Test?

    Read the article

  • The Krewe App Post-Mortem

    - by Chris Gardner
    Originally posted on: http://geekswithblogs.net/freestylecoding/archive/2014/05/23/the-krewe-app-post-mortem.aspxNow that teched has come and gone, I thought I would use this opportunity to do a little post-mortem on The Krewe app. It is one thing to test the app at home. It is a completely different animal to see how it responds in the environment TechEd creates. At a future time, I will list all the things that I would like to change with the app. At this point, I will find some good way to get community feedback. I want to break all this down screen by screen. We'll start with the screen I got right. The first of these is the events calendar. This is the one screen that, to you guys, just worked. However, there was an issue here. When I wrote v1 for last year, I was lazy and placed everything in CST. This caused problems with the achievements, which I will explain later. Furthermore, the event locations were not check-in locations. This created another problem with the achievements. Next, we get to the Twitter page. For what this page does, it works great. For those that don't know, I have an Azure Worker Role that polls Twitter pretty close to the rate limit. I cache these results in my database, and serve them upon request. This gives me great control over the content. I just have to remember to flush past tweets after a period, to save database growth. The next screen is the check-in screen. This screen has been the bane of my existence since I first created the thing. Last year, I used a background task to check people out of locations after they traveled. This year, I removed the background task in favor of a foursquare model. You are checked out after 3 hours or when you check-in to some other location. This seemed to work well, until those pesky achievements came into the mix. Again, more on this later. Next, I want to address the Connect and Connections screens together. I wanted to use some of the capabilities of the phone, and NFC seemed a natural choice. From this, I came up with the gamification aspects of the app. Since we are, fundamentally, a networking organization, I wanted to encourage people to actually network. Users could make and share a profile, similar to a virtual business card. I just had to figure out how to get people to use the feature. Why not just give someone a business card? Thus, the achievements were born. This was such a good idea. It would have been a great idea, if I have come up with it about two months earlier... When I came up with these ideas, I had about 2 weeks to implement them. Version 1 of the app was, basically, a pure consumption app. We provided data and centralized it. With version 2, the app became a much more interactive experience. The API was not ready for this change in such a short period of time. Most of this became apparent when I started implementing the achievements. The achievements based on count and specific person when fairly easy. The problem came with tying them to locations and events. This took some true SQL kung fu. This also showed me the rookie mistake of putting CST, not UTC, in the database. Once I got all of that cleaned up, I had to find a way to get the achievement system to talk to the phone. I knew I needed to be able to dynamically add achievements. I wouldn't know the precise location of some things until I got to Houston. I wanted the server to approve the achievements. This, unfortunately, required a decent data connection. Some achievements required GPS levels of location accuracy in areas of network triangulation. All of this became a huge nightmare. My flagship feature was based on some silly assumptions. Still, I managed to get 31 people to get the first achievement (Make 1 Connection.) Quite a few of those managed to get to the higher levels. Soon, I will post a list of the feature and changes that need to happen to the API. This includes things like proper objects for communication, geo-fencing, and caching. However, that is for another day.

    Read the article

  • Switch interface implementation using configuration

    - by Marcos
    We want to allow the same core service to be either fully implemented or, as other option, to be a proxy toward a client legacy system (via a WSDL for example). In that way, we have both implementation (proxy & full) and we switch which one to use in the configuration of the app. So in a nutshell, Some desired features: Two different implementation (proxy, full) instead of one implementation with a switch inside Switch implementation using configuration: dependency injection? reflection? Nice-to-have: the packaged delivered to the client doesn’t have to change depending on the choice between proxy or full Nice-to-have: Client can develop their custom implementation of the Core Interface and configure the applciation to use that one With this background, the question is: What alternatives we have to choose one implementation or other of an interface just changing configuration? Thanks

    Read the article

  • How to do the Geometry Wars gravity well effect

    - by Mykel Stone
    I'm not talking about the background grid here, I'm talking about the swirly particles going around the Gravity Wells! I've always liked the effect and decided it'd be a fun experiment to replicate it, I know GW uses Hooke's law all over the place, but I don't think the Particle-to-Well effect is done using springs, it looks like a distance-squared function. Here is a video demonstrating the effect: http://www.youtube.com/watch?v=YgJe0YI18Fg I can implement a spring or gravity effect on some particles just fine, that's easy. But I can't seem to get the effect to look similar to GWs effect. When I watch the effect in game it seems that the particles are emitted in bunches from the Well itself, they spiral outward around the center of the well, and eventually get flung outward, fall back towards the well, and repeat. How does he make the particles spiral outward when spawned? How does he keep the particle bunches together when near the Well but spread away from each other when they're flung outward? How does he keep the particles so strongly attached to the Well?

    Read the article

  • How I understood monads, part 1/2: sleepless and self-loathing in Seattle

    - by Bertrand Le Roy
    For some time now, I had been noticing some interest for monads, mostly in the form of unintelligible (to me) blog posts and comments saying “oh, yeah, that’s a monad” about random stuff as if it were absolutely obvious and if I didn’t know what they were talking about, I was probably an uneducated idiot, ignorant about the simplest and most fundamental concepts of functional programming. Fair enough, I am pretty much exactly that. Being the kind of guy who can spend eight years in college just to understand a few interesting concepts about the universe, I had to check it out and try to understand monads so that I too can say “oh, yeah, that’s a monad”. Man, was I hit hard in the face with the limitations of my own abstract thinking abilities. All the articles I could find about the subject seemed to be vaguely understandable at first but very quickly overloaded the very few concept slots I have available in my brain. They also seemed to be consistently using arcane notation that I was entirely unfamiliar with. It finally all clicked together one Friday afternoon during the team’s beer symposium when Louis was patient enough to break it down for me in a language I could understand (C#). I don’t know if being intoxicated helped. Feel free to read this with or without a drink in hand. So here it is in a nutshell: a monad allows you to manipulate stuff in interesting ways. Oh, OK, you might say. Yeah. Exactly. Let’s start with a trivial case: public static class Trivial { public static TResult Execute<T, TResult>( this T argument, Func<T, TResult> operation) { return operation(argument); } } This is not a monad. I removed most concepts here to start with something very simple. There is only one concept here: the idea of executing an operation on an object. This is of course trivial and it would actually be simpler to just apply that operation directly on the object. But please bear with me, this is our first baby step. Here’s how you use that thing: "some string" .Execute(s => s + " processed by trivial proto-monad.") .Execute(s => s + " And it's chainable!"); What we’re doing here is analogous to having an assembly chain in a factory: you can feed it raw material (the string here) and a number of machines that each implement a step in the manufacturing process and you can start building stuff. The Trivial class here represents the empty assembly chain, the conveyor belt if you will, but it doesn’t care what kind of raw material gets in, what gets out or what each machine is doing. It is pure process. A real monad will need a couple of additional concepts. Let’s say the conveyor belt needs the material to be processed to be contained in standardized boxes, just so that it can safely and efficiently be transported from machine to machine or so that tracking information can be attached to it. Each machine knows how to treat raw material or partly processed material, but it doesn’t know how to treat the boxes so the conveyor belt will have to extract the material from the box before feeding it into each machine, and it will have to box it back afterwards. This conveyor belt with boxes is essentially what a monad is. It has one method to box stuff, one to extract stuff from its box and one to feed stuff into a machine. So let’s reformulate the previous example but this time with the boxes, which will do nothing for the moment except containing stuff. public class Identity<T> { public Identity(T value) { Value = value; } public T Value { get; private set;} public static Identity<T> Unit(T value) { return new Identity<T>(value); } public static Identity<U> Bind<U>( Identity<T> argument, Func<T, Identity<U>> operation) { return operation(argument.Value); } } Now this is a true to the definition Monad, including the weird naming of the methods. It is the simplest monad, called the identity monad and of course it does nothing useful. Here’s how you use it: Identity<string>.Bind( Identity<string>.Unit("some string"), s => Identity<string>.Unit( s + " was processed by identity monad.")).Value That of course is seriously ugly. Note that the operation is responsible for re-boxing its result. That is a part of strict monads that I don’t quite get and I’ll take the liberty to lift that strange constraint in the next examples. To make this more readable and easier to use, let’s build a few extension methods: public static class IdentityExtensions { public static Identity<T> ToIdentity<T>(this T value) { return new Identity<T>(value); } public static Identity<U> Bind<T, U>( this Identity<T> argument, Func<T, U> operation) { return operation(argument.Value).ToIdentity(); } } With those, we can rewrite our code as follows: "some string".ToIdentity() .Bind(s => s + " was processed by monad extensions.") .Bind(s => s + " And it's chainable...") .Value; This is considerably simpler but still retains the qualities of a monad. But it is still pointless. Let’s look at a more useful example, the state monad, which is basically a monad where the boxes have a label. It’s useful to perform operations on arbitrary objects that have been enriched with an attached state object. public class Stateful<TValue, TState> { public Stateful(TValue value, TState state) { Value = value; State = state; } public TValue Value { get; private set; } public TState State { get; set; } } public static class StateExtensions { public static Stateful<TValue, TState> ToStateful<TValue, TState>( this TValue value, TState state) { return new Stateful<TValue, TState>(value, state); } public static Stateful<TResult, TState> Execute<TValue, TState, TResult>( this Stateful<TValue, TState> argument, Func<TValue, TResult> operation) { return operation(argument.Value) .ToStateful(argument.State); } } You can get a stateful version of any object by calling the ToStateful extension method, passing the state object in. You can then execute ordinary operations on the values while retaining the state: var statefulInt = 3.ToStateful("This is the state"); var processedStatefulInt = statefulInt .Execute(i => ++i) .Execute(i => i * 10) .Execute(i => i + 2); Console.WriteLine("Value: {0}; state: {1}", processedStatefulInt.Value, processedStatefulInt.State); This monad differs from the identity by enriching the boxes. There is another way to give value to the monad, which is to enrich the processing. An example of that is the writer monad, which can be typically used to log the operations that are being performed by the monad. Of course, the richest monads enrich both the boxes and the processing. That’s all for today. I hope with this you won’t have to go through the same process that I did to understand monads and that you haven’t gone into concept overload like I did. Next time, we’ll examine some examples that you already know but we will shine the monadic light, hopefully illuminating them in a whole new way. Realizing that this pattern is actually in many places but mostly unnoticed is what will enable the truly casual “oh, yes, that’s a monad” comments. Here’s the code for this article: http://weblogs.asp.net/blogs/bleroy/Samples/Monads.zip The Wikipedia article on monads: http://en.wikipedia.org/wiki/Monads_in_functional_programming This article was invaluable for me in understanding how to express the canonical monads in C# (interesting Linq stuff in there): http://blogs.msdn.com/b/wesdyer/archive/2008/01/11/the-marvels-of-monads.aspx

    Read the article

  • What discipline does Computer Science belong to?

    - by Macneil
    Is Computer Science science, applied mathematics, engineering, art, philosophy? "Other"? To provide background, here is Steven Wartik's blog posting for Scientific American titled "I'm not a real scientist, and that's okay." The article covers some good topics for this question, but it leaves open more than it answers. If you can think of the discipline, how would computer science fit into its definition? Should the discipline for Computer Science be based on what programmers do, or what academics do? What kind of answers do you get from people who've seemed to think deeply about this? What reasons do they give?

    Read the article

  • Understanding each other in web development

    - by Pete Hotchkin
    During my career I have been lucky enough to work in several different roles within web development with many extremely talented people, from incredible designers who were passionate about the placement of every pixel right through to server administrators and DBAs who were always measuring the improvements they were making to their queries in the smallest possible unit. The problem I always faced was that more often than not I was stuck in the middle trying to mediate between these different functions and enable each side to understand the other’s point of view. The main areas of contention that there have always been between these functional groups in my experience have been at 2 key points: during the build phase and then when there is a problem post-build. During both of these times it is often easier for someone to pass the buck onto someone else than spend the time to understand the other person’s perspective. Below is a quick look at two upcoming tools that will not only speed up the build phase for each function, but  also help when it comes to the issues faced once a site has been pushed live. In my experience a web project goes through several phases of development. The first of these is design, generally handled as Photoshop files which are then passed onto a front-end developer. This is the first point at which heated discussions can arise. One problem I’ve seen several times is that the designer doesn’t fully understand the platform constraints that need to be considered, and as a result has designed something that does not translate very well or is simply not possible. Working at Red Gate, I am lucky enough to be able to meet some amazing people and this happened just the other day when I was introduced to Neil Kinnish and Pete Nelson, the creators of what I believe could be a great asset in this designer-developer relationship, Mixture. Mixture allows the front end developer to quickly prototype a web page with built-in frameworks such as bootstrap. It’s not an IDE however, it just sits there in the background and monitors the project files in the background so every time you save a file from your favorite IDE, it will compile things like LESS, compact your JavaScript and the automatically refresh your test browser so you can see the changes instantly. I think one of the best parts of this however is a single button that pushes the changed files up to the web so the designer can instantly see how far the developer has got and the problem that he is facing at that time without the need to spend time setting up a remote server. I can see this being a real asset to remote teams where there needs to be a compromise between the designer and the front-end developer, or just to allow the designer to see how the build is progressing and suggest small alterations. Once the design has been built into the front end the designer’s job is generally done and there are no other points of contention between the designer and the other functions involved in building these web projects. As the project moves into the stage of integrating it into the back end and deploying it to the production server other functions start to be pulled in and other issues arise such as the back-end developer understanding the frameworks that they are using such as the routes that are in place in an MVC application or the number of database calls that the ORM layer is actually making. There are many tools out there that can actually help with these problems such as mini profiler that gives you a quick snapshot of what is going on directly in the browser. For a slightly more in-depth look at what is happening and to gain a deeper understanding of an application you may be working on though, you may want to consider Glimpse. Created by Nik and Anthony, it is an application that sits at the bottom of your browser (installed via NuGet) which can show you information about how your application is pieced together and how the information on screen is being delivered as it happens. With a wealth of community-built plugins such as one for nHibernate and linq2SQL (full list of plugins on NuGet). It can be customized directly to your own setup to truly delve into the code to see what is happening, and can help to reduce the number of confusing moments about whether it is your code that is going wrong or whether there is something more sinister happening directly on the server. All the tools that I have mentioned in this post help to do one thing above all, and that is to ease the barrier of understanding between the different functions that are involved in building and maintaining a web application. In my experience it is very easy to say “Well, that’s not my problem”, simply because the two functions involved don’t truly understand the other’s point of view. Software should not only be seen as a way to streamline our own working process or as a debugging tool but also a communication aid to improve the entire lifecycle of a web project. Glimpse is actually the project that I am the designer on and I would love to get your feedback if you do decide to try it out or if you would like to share your own experiences of working on web projects please fill in your details at https://www.surveymk.com/s/joinGlimpse  or add a comment below and I will get in touch with you.

    Read the article

  • Help with algorithmic complexity in custom merge sort implementation

    - by bitcycle
    I've got an implementation of the merge sort in C++ using a custom doubly linked list. I'm coming up with a big O complexity of n^2, based on the merge_sort() slice operation. But, from what I've read, this algorithm should be n*log(n), where the log has a base of two. Can someone help me determine if I'm just determining the complexity incorrectly, or if the implementation can/should be improved to achieve n*log(n) complexity? If you would like some background on my goals for this project, see my blog. I've added comments in the code outlining what I understand the complexity of each method to be. Clarification - I'm focusing on the C++ implementation with this question. I've got another implementation written in Python, but that was something that was added in addition to my original goal(s).

    Read the article

  • How Windows 8's Backup System Differs From Windows 7's

    - by Chris Hoffman
    Windows 8 contains a completely revamped backup system. Windows 8’s File History replaces Windows 7’s Windows Backup – if you use Windows Backup and update to Windows 8, you’ll find quite a few differences. Microsoft redesigned Windows’ backup features because less than 5% of PCs used Windows Backup. The new File History system is designed to be simple to set up and work automatically in the background. This post will focus on the differences between File History and the Windows Backup feature you may be familiar with from Windows 7 – check out our full walkthrough of File History for more information. HTG Explains: What The Windows Event Viewer Is and How You Can Use It HTG Explains: How Windows Uses The Task Scheduler for System Tasks HTG Explains: Why Do Hard Drives Show the Wrong Capacity in Windows?

    Read the article

  • What You Said: Do You Use the Command Line?

    - by Jason Fitzpatrick
    Earlier this week we asked you to sound off with your love (or lack there of) for the command line. You sounded off in force and now we’re back with a comment roundup. It turns out you all pretty much love the command line with that love ranging from not even liking Graphic User Interfaces (GUIs) to using the command line to get serious work done but having a long standing affair with your OS’s GUI. Many of you lamented the poor command line implementation in Windows—especially after you’d had experience with other operation systems. Mike writes: Of course. Some things are easier that was. Like ping and ipconfig. With a strong Unix background I still write and use batch files. It would be nice is the command line included more nice things like grep, sleep, touch. Maybe, someday, Windows will mature into a full OS. What is a Histogram, and How Can I Use it to Improve My Photos?How To Easily Access Your Home Network From Anywhere With DDNSHow To Recover After Your Email Password Is Compromised

    Read the article

  • How to access HTML elements from server side code in an asp.net website

    - by nikolaosk
    In this post I will demonstrate with a hands on example how HTML elements in an .aspx page can be processed exactly like standard ASP.Net server controls. Basically how to make them accessible from server side code. 1) Launch Visual Studio 2010/2008/2005. (express editions will work fine). Create a new empty website and choose a suitable name for it. Choose VB as the development language. 2) Add a new item in your site, a web form. Leave the default name. 3) Let's say that we want to change the background...(read more)

    Read the article

  • How to program for constraints/rules

    - by Gaurav
    First the background, during interviews in the past, many times I have been asked to design some or other variation of card game as programming puzzle, and I have tried to design it in OO way, but I have never been satisfied with my solutions. However it was not until recently that I realized that I had been approaching the problem from the wrong direction. Specifically I was trying to solve the problem by modeling individual card as an object. Problem with this is individual cards don't have any non-trivial intrinsic behavior and therefore are not suitable (or primary) candidate as objects. What is interesting and important about cards are rules and constraints, such as there could be only four suits, or only thirteen cards in each suit. Of course, then there are any number of rules for games. So my questions are Are there any idioms/constructs/patterns to program for rules & constraints. How many in 1 can be applied in conjunction with OO paradigm.

    Read the article

  • Is measuring software project metrics popular in todays industry?

    - by Russ K
    I encountered a developer who wanted some outside advice on their teams project. I found out they're developing a huge software suite for the companies executives, project manager and developers that can calculate metrics automatically and graph them per iteration. As a student from a computer science background I know very little on metrics and their importance, but my questions are: Do most companies have some way, doesn't have to be an elegant program, to measure meaningful metrics? Which metrics, single or combined, help you narrow down your projects scope and estimates? As a person who analyzes metrics, how often do you base decisions off of them? IE. Tests failed per week is increasing drastically? Do you feel that the introduction of studying metrics has helped you understand the project better? Not sure why but the developers project intrigued me and I must know more. If y

    Read the article

  • Organizations &amp; Architecture UNISA Studies &ndash; Chap 7

    - by MarkPearl
    Learning Outcomes Name different device categories Discuss the functions and structure of I/.O modules Describe the principles of Programmed I/O Describe the principles of Interrupt-driven I/O Describe the principles of DMA Discuss the evolution characteristic of I/O channels Describe different types of I/O interface Explain the principles of point-to-point and multipoint configurations Discuss the way in which a FireWire serial bus functions Discuss the principles of InfiniBand architecture External Devices An external device attaches to the computer by a link to an I/O module. The link is used to exchange control, status, and data between the I/O module and the external device. External devices can be classified into 3 categories… Human readable – e.g. video display Machine readable – e.g. magnetic disk Communications – e.g. wifi card I/O Modules An I/O module has two major functions… Interface to the processor and memory via the system bus or central switch Interface to one or more peripheral devices by tailored data links Module Functions The major functions or requirements for an I/O module fall into the following categories… Control and timing Processor communication Device communication Data buffering Error detection I/O function includes a control and timing requirement, to coordinate the flow of traffic between internal resources and external devices. Processor communication involves the following… Command decoding Data Status reporting Address recognition The I/O device must be able to perform device communication. This communication involves commands, status information, and data. An essential task of an I/O module is data buffering due to the relative slow speeds of most external devices. An I/O module is often responsible for error detection and for subsequently reporting errors to the processor. I/O Module Structure An I/O module functions to allow the processor to view a wide range of devices in a simple minded way. The I/O module may hide the details of timing, formats, and the electro mechanics of an external device so that the processor can function in terms of simple reads and write commands. An I/O channel/processor is an I/O module that takes on most of the detailed processing burden, presenting a high-level interface to the processor. There are 3 techniques are possible for I/O operations Programmed I/O Interrupt[t I/O DMA Access Programmed I/O When a processor is executing a program and encounters an instruction relating to I/O it executes that instruction by issuing a command to the appropriate I/O module. With programmed I/O, the I/O module will perform the requested action and then set the appropriate bits in the I/O status register. The I/O module takes no further actions to alert the processor. I/O Commands To execute an I/O related instruction, the processor issues an address, specifying the particular I/O module and external device, and an I/O command. There are four types of I/O commands that an I/O module may receive when it is addressed by a processor… Control – used to activate a peripheral and tell it what to do Test – Used to test various status conditions associated with an I/O module and its peripherals Read – Causes the I/O module to obtain an item of data from the peripheral and place it in an internal buffer Write – Causes the I/O module to take an item of data form the data bus and subsequently transmit that data item to the peripheral The main disadvantage of this technique is it is a time consuming process that keeps the processor busy needlessly I/O Instructions With programmed I/O there is a close correspondence between the I/O related instructions that the processor fetches from memory and the I/O commands that the processor issues to an I/O module to execute the instructions. Typically there will be many I/O devices connected through I/O modules to the system – each device is given a unique identifier or address – when the processor issues an I/O command, the command contains the address of the address of the desired device, thus each I/O module must interpret the address lines to determine if the command is for itself. When the processor, main memory and I/O share a common bus, two modes of addressing are possible… Memory mapped I/O Isolated I/O (for a detailed explanation read page 245 of book) The advantage of memory mapped I/O over isolated I/O is that it has a large repertoire of instructions that can be used, allowing more efficient programming. The disadvantage of memory mapped I/O over isolated I/O is that valuable memory address space is sued up. Interrupts driven I/O Interrupt driven I/O works as follows… The processor issues an I/O command to a module and then goes on to do some other useful work The I/O module will then interrupts the processor to request service when is is ready to exchange data with the processor The processor then executes the data transfer and then resumes its former processing Interrupt Processing The occurrence of an interrupt triggers a number of events, both in the processor hardware and in software. When an I/O device completes an I/O operations the following sequence of hardware events occurs… The device issues an interrupt signal to the processor The processor finishes execution of the current instruction before responding to the interrupt The processor tests for an interrupt – determines that there is one – and sends an acknowledgement signal to the device that issues the interrupt. The acknowledgement allows the device to remove its interrupt signal The processor now needs to prepare to transfer control to the interrupt routine. To begin, it needs to save information needed to resume the current program at the point of interrupt. The minimum information required is the status of the processor and the location of the next instruction to be executed. The processor now loads the program counter with the entry location of the interrupt-handling program that will respond to this interrupt. It also saves the values of the process registers because the Interrupt operation may modify these The interrupt handler processes the interrupt – this includes examination of status information relating to the I/O operation or other event that caused an interrupt When interrupt processing is complete, the saved register values are retrieved from the stack and restored to the registers Finally, the PSW and program counter values from the stack are restored. Design Issues Two design issues arise in implementing interrupt I/O Because there will be multiple I/O modules, how does the processor determine which device issued the interrupt? If multiple interrupts have occurred, how does the processor decide which one to process? Addressing device recognition, 4 general categories of techniques are in common use… Multiple interrupt lines Software poll Daisy chain Bus arbitration For a detailed explanation of these approaches read page 250 of the textbook. Interrupt driven I/O while more efficient than simple programmed I/O still requires the active intervention of the processor to transfer data between memory and an I/O module, and any data transfer must traverse a path through the processor. Thus is suffers from two inherent drawbacks… The I/O transfer rate is limited by the speed with which the processor can test and service a device The processor is tied up in managing an I/O transfer; a number of instructions must be executed for each I/O transfer Direct Memory Access When large volumes of data are to be moved, an efficient technique is direct memory access (DMA) DMA Function DMA involves an additional module on the system bus. The DMA module is capable of mimicking the processor and taking over control of the system from the processor. It needs to do this to transfer data to and from memory over the system bus. DMA must the bus only when the processor does not need it, or it must force the processor to suspend operation temporarily (most common – referred to as cycle stealing). When the processor wishes to read or write a block of data, it issues a command to the DMA module by sending to the DMA module the following information… Whether a read or write is requested using the read or write control line between the processor and the DMA module The address of the I/O device involved, communicated on the data lines The starting location in memory to read from or write to, communicated on the data lines and stored by the DMA module in its address register The number of words to be read or written, communicated via the data lines and stored in the data count register The processor then continues with other work, it delegates the I/O operation to the DMA module which transfers the entire block of data, one word at a time, directly to or from memory without going through the processor. When the transfer is complete, the DMA module sends an interrupt signal to the processor, this the processor is involved only at the beginning and end of the transfer. I/O Channels and Processors Characteristics of I/O Channels As one proceeds along the evolutionary path, more and more of the I/O function is performed without CPU involvement. The I/O channel represents an extension of the DMA concept. An I/O channel ahs the ability to execute I/O instructions, which gives it complete control over I/O operations. In a computer system with such devices, the CPU does not execute I/O instructions – such instructions are stored in main memory to be executed by a special purpose processor in the I/O channel itself. Two types of I/O channels are common A selector channel controls multiple high-speed devices. A multiplexor channel can handle I/O with multiple characters as fast as possible to multiple devices. The external interface: FireWire and InfiniBand Types of Interfaces One major characteristic of the interface is whether it is serial or parallel parallel interface – there are multiple lines connecting the I/O module and the peripheral, and multiple bits are transferred simultaneously serial interface – there is only one line used to transmit data, and bits must be transmitted one at a time With new generation serial interfaces, parallel interfaces are becoming less common. In either case, the I/O module must engage in a dialogue with the peripheral. In general terms the dialog may look as follows… The I/O module sends a control signal requesting permission to send data The peripheral acknowledges the request The I/O module transfers data The peripheral acknowledges receipt of data For a detailed explanation of FireWire and InfiniBand technology read page 264 – 270 of the textbook

    Read the article

< Previous Page | 425 426 427 428 429 430 431 432 433 434 435 436  | Next Page >