4 ms·

It was really the 386 that was the beginning of modern computing, since it had a mmu.

by CyberDildonics 6mo ago

theodorethomas 6mo ago
Except the 486 had hardware floating point, essential for technical work.
- CyberDildonics 6mo ago
  That's an advancement but that's a matter of speed an simplicity. An MMU is a huge before and after, it's still the biggest separator of CPUs today. The most important detail to understand a CPU is whether it has an MMU.
- II2II 6mo ago
  An MMU is pretty much necessary for robust multitasking. Without it, you are at the whim of how well software behaves. Without it, it is more difficult for developers to create well behaved software. That also assumes good intentions from programmers, since an MMU is necessary for memory protection (thus security). While emulating an FPU results in a huge performance penalty, it is only required in certain domains. In the world of IBM PCs, it was also possible to upgrade your system with an FPU after the fact. I don't recall seeing this option for IBM compatibles. While I have seen socketed MMUs on other systems, I don't know whether they were intended as upgrade options.
  - deleted 6mo ago
    [deleted]
- ciupicri 6mo ago
  By the way, "the i486SX was a microprocessor originally released by Intel in 1991. It was a modified Intel i486DX microprocessor with its floating-point unit (FPU) disabled." (https://en.wikipedia.org/wiki/I486SX https://en.wikipedia.org/wiki/I486SX)
- saati 6mo ago
  You could buy a 8087 for your 8086 or 8088, the 486DX just moved it on chip.
fulafel 6mo ago
Several operating systems on 286 (eg Xenix, Coherent, OS/2) used its MMU for multitasking and memory protection. See https://en.wikipedia.org/wiki/Intel_80286#Protected_mode https://en.wikipedia.org/wiki/Intel_80286#Protected_mode
- CyberDildonics 6mo ago
  Protected mode on the 286 allowed 24-bit addressing, enabling access to 16 MB of memory, but lacked virtual memory and required a reboot to return to real mode. The 386 introduced virtual memory through paging, 32-bit addressing for 4 GB of memory, and virtual 8086 mode for running multiple 8086 programs simultaneously without compromising security. https://flint.cs.yale.edu/feng/cos/resources/BIOS/procModes.htm https://flint.cs.yale.edu/feng/cos/resources/BIOS/procModes.... https://en.wikipedia.org/wiki/Protected_mode https://en.wikipedia.org/wiki/Protected_mode
- zozbot234 6mo ago
  The 286 protected mode did not allow for a 32-bit flat address space and was heavily half-baked in other ways, e.g. no inbuilt way to return the CPU to real mode without a slow and fiddly CPU-reset.
  - fulafel 6mo ago
    It was architecturally a 16-bit CPU so a flat 32-bit address space would be a non sequitur. If you wanted flat 32-bit addressing, there was a contemporary chip that could do it with virtual memory: Motorola 68010 + the optional external MMU. (Or if you were willing to do some hoops, even a 68000.. see the Sun-1)
- icedchai 6mo ago
  Coherent was the first Unix-like OS I ran, on a 386SX box. I think it was Coherent 4.x.

It was really the 386 that was the beginning of modern computing, since it had a mmu.

theodorethomas 6mo ago

Except the 486 had hardware floating point, essential for technical work.

CyberDildonics 6mo ago
That's an advancement but that's a matter of speed an simplicity. An MMU is a huge before and after, it's still the biggest separator of CPUs today. The most important detail to understand a CPU is whether it has an MMU.
II2II 6mo ago
An MMU is pretty much necessary for robust multitasking. Without it, you are at the whim of how well software behaves. Without it, it is more difficult for developers to create well behaved software. That also assumes good intentions from programmers, since an MMU is necessary for memory protection (thus security). While emulating an FPU results in a huge performance penalty, it is only required in certain domains. In the world of IBM PCs, it was also possible to upgrade your system with an FPU after the fact. I don't recall seeing this option for IBM compatibles. While I have seen socketed MMUs on other systems, I don't know whether they were intended as upgrade options.
- deleted 6mo ago
  [deleted]
ciupicri 6mo ago
By the way, "the i486SX was a microprocessor originally released by Intel in 1991. It was a modified Intel i486DX microprocessor with its floating-point unit (FPU) disabled." (https://en.wikipedia.org/wiki/I486SX https://en.wikipedia.org/wiki/I486SX)
saati 6mo ago
You could buy a 8087 for your 8086 or 8088, the 486DX just moved it on chip.

fulafel 6mo ago

Several operating systems on 286 (eg Xenix, Coherent, OS/2) used its MMU for multitasking and memory protection. See https://en.wikipedia.org/wiki/Intel_80286#Protected_mode https://en.wikipedia.org/wiki/Intel_80286#Protected_mode

CyberDildonics 6mo ago
Protected mode on the 286 allowed 24-bit addressing, enabling access to 16 MB of memory, but lacked virtual memory and required a reboot to return to real mode. The 386 introduced virtual memory through paging, 32-bit addressing for 4 GB of memory, and virtual 8086 mode for running multiple 8086 programs simultaneously without compromising security. https://flint.cs.yale.edu/feng/cos/resources/BIOS/procModes.htm https://flint.cs.yale.edu/feng/cos/resources/BIOS/procModes.... https://en.wikipedia.org/wiki/Protected_mode https://en.wikipedia.org/wiki/Protected_mode
zozbot234 6mo ago
The 286 protected mode did not allow for a 32-bit flat address space and was heavily half-baked in other ways, e.g. no inbuilt way to return the CPU to real mode without a slow and fiddly CPU-reset.
- fulafel 6mo ago
  It was architecturally a 16-bit CPU so a flat 32-bit address space would be a non sequitur. If you wanted flat 32-bit addressing, there was a contemporary chip that could do it with virtual memory: Motorola 68010 + the optional external MMU. (Or if you were willing to do some hoops, even a 68000.. see the Sun-1)
icedchai 6mo ago
Coherent was the first Unix-like OS I ran, on a 386SX box. I think it was Coherent 4.x.