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FPU and MMX in x64?

Jose Barreto - MSFT — Thu, 26 May 2005 23:26:08 GMT

From: levicki
Sent: Wednesday, May 25, 2005 8:41 PM
Subject: FPU and MMX in x64?

I have read somewhere in MSDN (perhaps it was in DDK part) that Windows x64 will not preserve state of FPU and MMX registers across context switch and that the code written to take advantage of FPU and MMX will not work. Does that still apply and if it does what is the scope? 64-bit apps, drivers, 32-bit apps or all of them?

From: Program Manager in Visual C++ Group
Sent: Thursday, May 26, 2005 10:38 AM

It does preserve the state. It's the DDK page that has stale information, which I've requested it to be changed. Let them know that the OS does preserve state of x87 and MMX registers on context switches.

From: Software Engineer in Windows Kernel Group
Sent: Thursday, May 26, 2005 11:06 AM

For user threads the state of legacy floating point is preserved at context switch. But it is not true for kernel threads. Kernel mode drivers can not use legacy floating point instructions.

64 bits

Either 64bit mode or floating-point ? | keyongtech

FPU and MMX in x64?