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> if Intel had decided to make the x86 segment paragraph size 256 bytes (8 bits) instead of the useless 4 bits It would also have increased memory fragmentatio
by cesarb 6y ago
> if Intel had decided to make the x86 segment paragraph size 256 bytes (8 bits) instead of the useless 4 bits
It would also have increased memory fragmentation. Many memory allocations were aligned to a segment boundary, so you'd be wasting up to 255 bytes instead of up to 15 bytes on each allocation.
- mrlonglong 6y agoActually there aren't any alignment issues with the 8086, as it's still a 8 bit processor at heart.
- mschaef 6y agoSegment alignment. Not read alignment. Large model memory allocators would allocate memory on segment boundaries. This is more or less essential if you need to use more than 64K of memory in your program. An 8-bit paragraph size (rather than the 4 that were used) would've forced all segment allocations to 256-byte boundaries, so that's where the fragmentation issue comes from. Steve Morse (one of the designers of the chip) talks about the issue in page 16 of this: https://www.stevemorse.org/8086history/8086history.pdf https://www.stevemorse.org/8086history/8086history.pdf