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I still think you fail to realize how significant it is that Z80 CP/M is an 8bit operating system and every version of DOS is a 16bit operating system. You cou

I still think you fail to realize how significant it is that Z80 CP/M is an 8bit operating system and every version of DOS is a 16bit operating system. You could probably steal some ideas but any sort of translation makes no sense. If it was that easy, Digital Research would have had their OS done first. DOS was designed to run re-compiled CP/M programs with minimal changes. And some people translated 8080 programs to run on 8086 but they're still just 8bit programs. An operating system needs to be optimized and customized for the CPU it runs on. You're not going achieve much of value taking OS code from a different lesser CPU.

anonymousiam 3y ago
The 8080 and Z-80 had 16-bit registers and could do some limited 16-bit arithmetic. The 8088 (used in the first IBM PC) used an 8-bit bus to communicate with memory and I/O. The 8086 had a 16-bit bus. CompuPro had an 8086 S-100 board, which may have been the first target for DOS, but I cannot recall for certain. Both 8086 and 8088 ran in what is now called "real mode", which allows direct access to only 64k of RAM (just like the 8080 and Z-80). To access more than 64k at a time, you had to use segment registers. CP/M 3 (x80) employed bank-switching, which was a similar technique, but done with hardware that was external to the CPU instead of built-in. There really wasn't much difference between the Z-80 and the 8086 in terms of performance. Yeah, the 8086 had a 16-bit bus, but the instructions were 16-bits too, so running a program from non-cached RAM (because there wasn't any such thing as RAM cache then) was about the same. The 8088 (at 4.77MHz) would under-perform when compared with a (4MHz) Z-80, because they both used an 8-bit bus, but the Z-80 needed only one memory fetch per instruction, vs. two for the 8088. https://en.wikipedia.org/wiki/X86_memory_segmentation https://en.wikipedia.org/wiki/X86_memory_segmentation I do not fail to realize anything, but I'm wondering why you are so passionate about trying to disprove that SCP/Tim Patterson ripped off DR/Gary Kildall's code to produce QDOS when there is so much strong evidence that he did.

anonymousiam 3y ago

The 8080 and Z-80 had 16-bit registers and could do some limited 16-bit arithmetic. The 8088 (used in the first IBM PC) used an 8-bit bus to communicate with memory and I/O. The 8086 had a 16-bit bus. CompuPro had an 8086 S-100 board, which may have been the first target for DOS, but I cannot recall for certain. Both 8086 and 8088 ran in what is now called "real mode", which allows direct access to only 64k of RAM (just like the 8080 and Z-80). To access more than 64k at a time, you had to use segment registers. CP/M 3 (x80) employed bank-switching, which was a similar technique, but done with hardware that was external to the CPU instead of built-in. There really wasn't much difference between the Z-80 and the 8086 in terms of performance. Yeah, the 8086 had a 16-bit bus, but the instructions were 16-bits too, so running a program from non-cached RAM (because there wasn't any such thing as RAM cache then) was about the same. The 8088 (at 4.77MHz) would under-perform when compared with a (4MHz) Z-80, because they both used an 8-bit bus, but the Z-80 needed only one memory fetch per instruction, vs. two for the 8088. https://en.wikipedia.org/wiki/X86_memory_segmentation https://en.wikipedia.org/wiki/X86_memory_segmentation I do not fail to realize anything, but I'm wondering why you are so passionate about trying to disprove that SCP/Tim Patterson ripped off DR/Gary Kildall's code to produce QDOS when there is so much strong evidence that he did.