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The 80286 was a pretty weird CPU. I don't think Intel anticipated that it would be primarily used for faster IBM PC compatibles. Wikipedia seems to confirm thi

by pavlov 6y ago

The 80286 was a pretty weird CPU. I don't think Intel anticipated that it would be primarily used for faster IBM PC compatibles. Wikipedia seems to confirm this: "Intel did not expect personal computers to use the 286. The CPU was designed for multi-user systems with multitasking applications, including communications (such as automated PBXs) and real-time process control." [https://en.wikipedia.org/wiki/Intel_80286 https://en.wikipedia.org/wiki/Intel_80286]

mschaef 6y ago
Around this time there was another significant CPU architecture in play at Intel, the iAPX 432. The 432 was the intentional follow on to the 8-bit series (8080) and suffered from a number of the usual second system effects - it was big, complicated, and slow. The 8086/8 was a stop gap measure while the 432 was being sorted out, and my understanding is also that the 8087 math chip was essentially a 432 component that had been redesigned to work with the other chip series. Viewed in the context of the 432, it's not hard to imagine Intel viewing an 8086 follow on chip as a niche market CPU while their would-be-anointed successor takes the more mainstream PC market. What's maybe more interesting to consider is the role of the 80386, and how its design process might have gone. By the time of the 80386, Intel built in features to the chip explicitly useful for the purpose of bringing multitasking to the PC space. One of the 386's many noteworthy features, was 'V86' mode, which was designed to allow it to easily multitask multiple real mode 8086/8 apps at the same time. This was essentially a 'run several DOS programs at once' feature, and there were a couple major PC "OS"'s that used it - most notably Windows/386 and DesqView/386. (You should also note that this is not close to the first time that Intel tried to get away from x86 - the iAPX 432, i860, and Itanium all represent varying attempts to achieve that goal.)
- TedDoesntTalk 6y ago
  What was Windows/386?
  - pavlov 6y ago
    IIRC, it was a version of Windows 2.1 which could multitask DOS applications using the 8086 virtualization mode available on the i386.
  - mschaef 6y ago
    pavlov is right. Early versions of Windows all ran in real mode. Multiple Windows programs were loaded into the same real mode address space (no protection) and co-operatively multitasked based on the GUI's messaging infrastructure. (A program could just stop processing GUI messages and totally monopolize the CPU.) There was also some limited support for memory relocation via a block lock/unlock mechanism built into the memory manager. If you wanted to run a DOS program, this was all suspended, with the DOS program given control over the full machine in the interim. What Windows/386 did is put a 386-specific V86 multitasker called VMM underneath all of this. This multitasker had isolation between the processes it ran, one of which would be the Windows GUI environment I described above and others could be other DOS Programs, for which there were also provisions to put the output into a window of the GUI. This is really the first moment Windows got protected mode support, although none of the user processes actually saw the larger address space. It's Windows 3.0 that let the GUI itself run in protected mode, albeit still with 64K segmentation. Combined with some graphics and usability improvements in 3.0, this is really why 3.0 'got it right' in terms of feature set and price point. Windows for Workgroups 3.11 then moved the file system to protected mode, a product called Win32s let Windows programs themselves use 32-bit segment addressing, and combination of all of that that was the foundation for the 'fully 32-bit' Windows 95, which just moved a bunch more functionality into 32-bit code and the VMM 32-bit multitasker originally introduced in Windows/386.
    - Narishma 6y ago
      > This is really the first moment Windows got protected mode support, although none of the user processes actually saw the larger address space. What about the 286 protected mode support. Did that come later?
      - mschaef 6y ago
- pavlov 6y ago
  > "...Intel tried to get away from x86 - the iAPX 432, i860, and Itanium all represent varying attempts to achieve that goal." It's a strange irony that none of these homegrown attempts worked out, but x86 is now threatened by the one external architecture where Intel was a performance leader in 2000-2005 with their StrongARM / XScale chips. Intel giving up on ARM in 2006 was IMO one of the greatest strategic blunders of all time.

by pavlov 6y ago

mschaef 6y ago

Around this time there was another significant CPU architecture in play at Intel, the iAPX 432. The 432 was the intentional follow on to the 8-bit series (8080) and suffered from a number of the usual second system effects - it was big, complicated, and slow. The 8086/8 was a stop gap measure while the 432 was being sorted out, and my understanding is also that the 8087 math chip was essentially a 432 component that had been redesigned to work with the other chip series. Viewed in the context of the 432, it's not hard to imagine Intel viewing an 8086 follow on chip as a niche market CPU while their would-be-anointed successor takes the more mainstream PC market. What's maybe more interesting to consider is the role of the 80386, and how its design process might have gone. By the time of the 80386, Intel built in features to the chip explicitly useful for the purpose of bringing multitasking to the PC space. One of the 386's many noteworthy features, was 'V86' mode, which was designed to allow it to easily multitask multiple real mode 8086/8 apps at the same time. This was essentially a 'run several DOS programs at once' feature, and there were a couple major PC "OS"'s that used it - most notably Windows/386 and DesqView/386. (You should also note that this is not close to the first time that Intel tried to get away from x86 - the iAPX 432, i860, and Itanium all represent varying attempts to achieve that goal.)

TedDoesntTalk 6y ago
What was Windows/386?
- pavlov 6y ago
  IIRC, it was a version of Windows 2.1 which could multitask DOS applications using the 8086 virtualization mode available on the i386.
- mschaef 6y ago
  pavlov is right. Early versions of Windows all ran in real mode. Multiple Windows programs were loaded into the same real mode address space (no protection) and co-operatively multitasked based on the GUI's messaging infrastructure. (A program could just stop processing GUI messages and totally monopolize the CPU.) There was also some limited support for memory relocation via a block lock/unlock mechanism built into the memory manager. If you wanted to run a DOS program, this was all suspended, with the DOS program given control over the full machine in the interim. What Windows/386 did is put a 386-specific V86 multitasker called VMM underneath all of this. This multitasker had isolation between the processes it ran, one of which would be the Windows GUI environment I described above and others could be other DOS Programs, for which there were also provisions to put the output into a window of the GUI. This is really the first moment Windows got protected mode support, although none of the user processes actually saw the larger address space. It's Windows 3.0 that let the GUI itself run in protected mode, albeit still with 64K segmentation. Combined with some graphics and usability improvements in 3.0, this is really why 3.0 'got it right' in terms of feature set and price point. Windows for Workgroups 3.11 then moved the file system to protected mode, a product called Win32s let Windows programs themselves use 32-bit segment addressing, and combination of all of that that was the foundation for the 'fully 32-bit' Windows 95, which just moved a bunch more functionality into 32-bit code and the VMM 32-bit multitasker originally introduced in Windows/386.
  - Narishma 6y ago
    > This is really the first moment Windows got protected mode support, although none of the user processes actually saw the larger address space. What about the 286 protected mode support. Did that come later?
    - mschaef 6y ago
pavlov 6y ago
> "...Intel tried to get away from x86 - the iAPX 432, i860, and Itanium all represent varying attempts to achieve that goal." It's a strange irony that none of these homegrown attempts worked out, but x86 is now threatened by the one external architecture where Intel was a performance leader in 2000-2005 with their StrongARM / XScale chips. Intel giving up on ARM in 2006 was IMO one of the greatest strategic blunders of all time.