5 ms·

One of the big selling points of x86 is backwards compatibility. If you have some OS from 1990 you can still run it (without emulation or virtualization, so lon

by rdmsr 9y ago

One of the big selling points of x86 is backwards compatibility. If you have some OS from 1990 you can still run it (without emulation or virtualization, so long as it doesn't depend on clock speed), which is pretty crazy. Slight aside, there are a lot of reasons that Itanium failed, but certainly one of them was lack of backwards compatibility.

dom0 9y ago
> Slight aside, there are a lot of reasons that Itanium failed, but certainly one of them was lack of backwards compatibility. Itanium did not aim at the x86 market. The x86 translation layer was retrospectively seen as a mistake as well, because it wasn't relevant, but required transistors that limited the design's performance overall, which was relevant.
- cwyers 9y ago
  > Itanium did not aim at the x86 market. Maybe not. But x86 certainly took over the market Itanium was aiming for.
  - nine_k 9y ago
    x86 did not. x64 did.
    - cwyers 9y ago
      All 16 and 32 bit x86 code is valid on x64. It's an extension, not a new ISA.
      - geezerjay 9y ago
        You got it all backwards. AMD64 is a complete revamp which happens to support x86 in its legacy mode. Server people care for 64-bit address spaces, and that's a feature introduced by AMD64 which is not available in x86.
pcwalton 9y ago
Itanium was extraordinarily backwards incompatible. There's an enormous gulf between "runs software from the 80s" (which is something the PC platform only pretends to do anyway, because peripherals now are incompatible) and "can't run Windows at all". Breaking v8086 mode wouldn't prevent modern Windows from working (which is in fact why this bug wasn't noticed). You can't even enter it from long mode to begin with!
- merb 9y ago
  actually my windows 10 installation didn't used uefi. (I had a really old machine). Basically I upgrade/upgraded to ryzen. I don't think it will be easy to migrate to UEFI straight.
volkl47 9y ago
This is also one of the main reasons why Mainframes still exist. Backwards compatibility straight back to 1964 is a big deal, there's lots of 50+ year old code still in production at banks, insurers, and the like.
kobeya 9y ago
Pedantic point, but you couldn't really run an OS from 1990. It wouldn't support any modern peripheral buses required for normal operation. But you certainly can natively run user-mode 16-bit DOS programs on a modern CPU.

by rdmsr 9y ago

dom0 9y ago

> Slight aside, there are a lot of reasons that Itanium failed, but certainly one of them was lack of backwards compatibility. Itanium did not aim at the x86 market. The x86 translation layer was retrospectively seen as a mistake as well, because it wasn't relevant, but required transistors that limited the design's performance overall, which was relevant.

cwyers 9y ago
> Itanium did not aim at the x86 market. Maybe not. But x86 certainly took over the market Itanium was aiming for.
- nine_k 9y ago
  x86 did not. x64 did.
  - cwyers 9y ago
    All 16 and 32 bit x86 code is valid on x64. It's an extension, not a new ISA.
    - geezerjay 9y ago
      You got it all backwards. AMD64 is a complete revamp which happens to support x86 in its legacy mode. Server people care for 64-bit address spaces, and that's a feature introduced by AMD64 which is not available in x86.

pcwalton 9y ago

Itanium was extraordinarily backwards incompatible. There's an enormous gulf between "runs software from the 80s" (which is something the PC platform only pretends to do anyway, because peripherals now are incompatible) and "can't run Windows at all". Breaking v8086 mode wouldn't prevent modern Windows from working (which is in fact why this bug wasn't noticed). You can't even enter it from long mode to begin with!

merb 9y ago
actually my windows 10 installation didn't used uefi. (I had a really old machine). Basically I upgrade/upgraded to ryzen. I don't think it will be easy to migrate to UEFI straight.

volkl47 9y ago

This is also one of the main reasons why Mainframes still exist. Backwards compatibility straight back to 1964 is a big deal, there's lots of 50+ year old code still in production at banks, insurers, and the like.

kobeya 9y ago

Pedantic point, but you couldn't really run an OS from 1990. It wouldn't support any modern peripheral buses required for normal operation. But you certainly can natively run user-mode 16-bit DOS programs on a modern CPU.