4 ms·

In 1989, people very much used real mode, so it's not surprising this failed. (also, it was for embedded systems only according to that Wikipedia article) In 2

by senko 4y ago

In 1989, people very much used real mode, so it's not surprising this failed. (also, it was for embedded systems only according to that Wikipedia article) In 2023, not so much. It's baffling to me this is still supported, when all the other changes in the hardware basically make it impossible to run anything that old on the modern hardware (you can do that in QEMU, but you can then emulate x86 in software fast enough anyway).

voxadam 4y ago
What's the actual reason for real mode still being supported on modern processors in this day in age? Why didn't it die with the advent of AMD64 (aka x86-64)? Why didn't AMD skip real mode and boot directly into something more modern?
- pwg 4y ago
  Most likely because for protected mode to function, there is a certain minimal amount of housekeeping data tables that need to be setup properly (i.e. LDT, GDT, IDT, etc), otherwise you'll just immediately take a double fault and the CPU will halt. Real mode exists today as a gateway to setting up all those housekeeping data tables so that once the "protected mode" switch is flipped on, the CPU will actually find code to execute.
- gpderetta 4y ago
  - There is likely very little to no cost in keeping it in - There might be even a cost in removing it. - Complexity is a barrier to entry to any competitor that want to produce compatible CPUs.
- toast0 4y ago
  When AMD64 came out, bios booting was dominant. You need real mode for that. In today's world, you could probably release an UEFI only cpu and few would notice. But I doubt it would save enough space to make a difference. And you'd open yourself to criticism from those few that still use real mode: this processor is fake, they'd say, because it has no real mode.
  - sgjohnson 4y ago
    > this processor is fake, they'd say, because it has no real mode. They could also claim that it’s not PC compatible. Because it literally wouldn’t be. Apple also achieved their dream of the Mac no longer being a PC with the release of M1.
kevin_thibedeau 4y ago
I boot FreeDOS on a Ryzen system so I can use a parallel port device whose program won't work correctly under 64-bit Dosemu2. it is an EPROM programmer whose timing requirements won't tolerate non-virtualized emulation.
- senko 4y ago
  Thanks for providing an actual and relevant use case. TBH (and I'm wildly speculating here, I'm not involved in embedded dev at all), if there were no other options, I believe the SW emulation would rise to the challenge to make it workable. If people can faithfully reproduce behaviours of ages old consoles to make sure the old games' bugs are still preserved, and for free, I'm guessing someone would step up in case of x86 if there was a business need. But since you can still use actual HW to do that, there isn't any.

by senko 4y ago

voxadam 4y ago

What's the actual reason for real mode still being supported on modern processors in this day in age? Why didn't it die with the advent of AMD64 (aka x86-64)? Why didn't AMD skip real mode and boot directly into something more modern?

pwg 4y ago
Most likely because for protected mode to function, there is a certain minimal amount of housekeeping data tables that need to be setup properly (i.e. LDT, GDT, IDT, etc), otherwise you'll just immediately take a double fault and the CPU will halt. Real mode exists today as a gateway to setting up all those housekeeping data tables so that once the "protected mode" switch is flipped on, the CPU will actually find code to execute.
gpderetta 4y ago
- There is likely very little to no cost in keeping it in - There might be even a cost in removing it. - Complexity is a barrier to entry to any competitor that want to produce compatible CPUs.
toast0 4y ago
When AMD64 came out, bios booting was dominant. You need real mode for that. In today's world, you could probably release an UEFI only cpu and few would notice. But I doubt it would save enough space to make a difference. And you'd open yourself to criticism from those few that still use real mode: this processor is fake, they'd say, because it has no real mode.
- sgjohnson 4y ago
  > this processor is fake, they'd say, because it has no real mode. They could also claim that it’s not PC compatible. Because it literally wouldn’t be. Apple also achieved their dream of the Mac no longer being a PC with the release of M1.

kevin_thibedeau 4y ago

I boot FreeDOS on a Ryzen system so I can use a parallel port device whose program won't work correctly under 64-bit Dosemu2. it is an EPROM programmer whose timing requirements won't tolerate non-virtualized emulation.

senko 4y ago
Thanks for providing an actual and relevant use case. TBH (and I'm wildly speculating here, I'm not involved in embedded dev at all), if there were no other options, I believe the SW emulation would rise to the challenge to make it workable. If people can faithfully reproduce behaviours of ages old consoles to make sure the old games' bugs are still preserved, and for free, I'm guessing someone would step up in case of x86 if there was a business need. But since you can still use actual HW to do that, there isn't any.