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Athlon 64: How AMD turned the tables on Intel

(dfarq.homeip.net)
331 points giuliomagnifico | 1 comments | 25 Sep 25 18:09 UTC | HN request time: 0.204s | source
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deaddodo ◴[25 Sep 25 20:01 UTC] No.45378189[source]▶
Nitpick: The author states that removal of 16-bit in Windows 64 was a design decision and not a technical one. That’s not quite true.

When AMD64 is in one of the 64-bit modes, long mode (true 64-bit) or compatibility mode (64-bit with 32-bit compatibility), you can not execute 16-bit code. There are tricks to make it happen, but they all require switching the CPU mode, which is insecure and can cause problems in complex execution environments (such as an OS).

If Microsoft (or Linux, Apple, etc) wanted to support 16-bit code in their 64-bit OSes, they would have had to create an emulator+VM (such as OTVDM/WineVDM) or make costly hacks to the OS.

replies(3): >>45378270 #>>45378503 #>>45378862 #
1. Animats ◴[25 Sep 25 20:49 UTC] No.45378862[source]▶
It's not so much running 16 bit code, but running something that wants to run on bare metal, i.e. DOS programs that access hardware directly. Maintaining the DOS virtualization box well into the 21st century probably wasn't worth it.

> The 64-bit builds of Windows weren’t available immediately.

There was a year or so between the release of AMD-64 and the first shipping Microsoft OS that supported it.[1] It was rumored that Intel didn't want Microsoft to support AMD-64 until Intel had compatible hardware. Anyone know? Meanwhile, Linux for AMD-64 was shipping, which meant Linux was getting more market share in data centers.[1]