80286 ATX mainboard based on the IBM 5170 AT PC

Re:80286 ATX mainboard based on the IBM 5170 AT PC by rep_lodsb on Wednesday November 13, 2024 @11:14AM (#42127334)

Turbo Pascal actually didn't: IIRC versions 3.x and lower used the "small" model (they were also available for CP/M on Z80, where 64K was the entire address space anyway), then newer ones exclusively the "large" one.

TP forcing use of large pointers for everything, and its lack of even trivial peephole optimizations, probably contributed to the myth that C was somehow inherently more efficient.

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Re:80286 ATX mainboard based on the IBM 5170 AT PC by burnt-resistor on Thursday November 14, 2024 @11:20AM (#42137720)

You misremembered.

[BT]P7 includes for compatibility: tiny (.COM), small, compact, medium, large, and large w/ overlays (which can use EMS when available). There are DPMI clients for [BT]P7 that make it possible to switch to protected mode and use more memory.

It definitely generated offset-only pointers in the tiny, small, and medium memory models because that's how they referred to data with the common DS segment. I did plenty of memory and instruction-level debugging in [BT] Profiler/Debugger and inspected plenty of pointers where they lived in RAM.

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Re:80286 ATX mainboard based on the IBM 5170 AT PC by rep_lodsb on Thursday November 14, 2024 @03:20PM (#42140751)

What command line option or compiler directive can I use to create a .COM program? How do I declare a near pointer variable?

http://bitsavers.trailing-edge.com/pdf/borland/turbo_pascal/...

Page 221: "A Pointer type is stored as two words"

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