Title says it all. "address 0x500 is the last one used by the BIOS" - en.wikipedia.org/wiki/Master_boot_record "00000000-000003FF Real Mode IVT (Interrupt Vector Table)" - wiki.osdev.org/Memory_Map_%28x86%29 So can you tell me why NASM places my .com file's stack pointer to 0x3FF while my instruction pointer starts at 0x7c00? To me the most intuitive place for SP would be right below 0x7c00. Thanks.