What's the situation regarding the 64bit executable?

[ZaltysZ]

Originally Posted by louisv

Remember the days of 16bit ? The 286, 386 ?

Programs were quite a bit smaller then, with an address space of 2 to the 16th power being 64K on the 8088, the first PCs. The 286 and 386 had a bigger space of 1MB, or 20bit of address space.

8088 had 16-bit registers, so only 16-bit long addresses were possible, what gave those 64KB. However, there were also possible to use segmented memory access, which combined segment selector and offset to allow access more memory than 64KB. Hardware had means to use 20-bit address space (1MB), which could be accessible by software via segmented access. Usually 640KB were available to user, and upper region were used by BIOS.

268 and 386 added 24-bit and 32-bit protected modes respectively, whose extended available address spaces to 16MB and 4GB.