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The Wide World Of The AMD64
The NT Insider | Published: 13-Jun-03| Modified: 22-Jun-03
Unless you've been living under a rock, you've heard that AMD has introduced a new 64-bit processor. Code named the "Hammer" family of processors, the AMD Opteron and Athlon-64 are poised to kick the normally evolution-prone world of x86 computing into revolution. This article provides a brief introduction to some of the architectural highlights of the Hammer family, and the forthcoming support for the AMD64 on 64-bit Windows systems.
It’s Compatible and Fast
The AMD-64 can operate in one of two modes: Legacy Mode or Long Mode.
In Legacy Mode, the AMD-64 appears for all intents and purposes like a standard 32-bit x86 system. It runs ordinary versions of Windows. In this mode, it uses a 32-bit operating system and standard 32-bit drivers. It runs 32-bit applications unchanged. From our brief tests, the AMD-64 appeared to run in Legacy Mode as fast as any other modern system running the same software.....
....Rarely do we find a system where so many things seem to have been done right. What’s irritated you over the years about the X86 architecture? Chances are it’s been fixed in the AMD-64, running in Long Mode’s 64-bit sub mode.
One thing that’s long irritated me about the x86 is the paucity of general purpose registers. The AMD-64 fixes that by adding eight new general purpose registers, numbered R8 through R15. Of course, the entire register set has been lengthened to 64 bits. The full 64-bit width of each register is accessed by using the “R” prefix. So, for example, as is traditional, AX is a 16-bit register and EAX is the 32-bit designation for this same register. The 64-bit version of this register is accessed by specifying RAX.
The new registers, numbered R8 through R15, can also use explicit width designators. For example, R8W designates the low 16 bits of R8, and the 32 bit designation for that same register is R8D. Sweet, huh?
How about those annoying segment registers? The AMD-64 does away with them when running native 64-bit code. In their place, flat addressing is used.
Perhaps the cumbersome X87 floating point instructions and register set is your hot-button. Well, to maintain compatibility for existing 32-bit programs, the AMD-64 includes those old X87 registers and indeed supports the X87 FP instruction set. But 64-bit versions of Windows only support these registers for 32-bit programs running in compatibility sub-mode. For 64-bit mode programs, floating point and media operations are supported exclusively by the 128-bit XMM registers (used by SSE/SSE2 instructions). Like the GP register set, the XMM register set has also been augmented with the edition of 8 new XMM registers (numbered XMM8 through XMM15). The floating point parts of the C run-time library have been re-written to use SSE/SSE2 instructions for floating point operations. And, are you ready for the best news yet for driver writers? The SSE/SSE2 instruction set is fully-supported in kernel-mode, and is automatically context switched. No more goofy calls to KeSaveFloatingPointState() required if you need FP or media-specific instructions.
What About Windows?
When running under 64-bit Windows on the AMD-64, 32-bit apps have access to either a 2GB or 4GB virtual address space depending on whether or not they are large address aware. Apps that are re-compiled to native 64-bit mode will get an address space of about 8TB.
What does the kernel-mode address space look like? Well, there’s 248TB (that’s not a typo – two hundred and forty eight terabytes is correct) of kernel virtual address space. The paged and non-paged pools each are allocated 128GB of address space; System cache gets 1TB of address space. I’m thiknin’ that’s enough address space for awhile. I’ll call you when I run out, assuming I’m still around.
As mentioned previously, 32-bit apps run under the 64-bit version of Windows without translation or emulation. The only “help” such applications receive is that 32-bit system service calls are “thunked” (extended) to their 64-bit equivalents. This is entirely transparent to the application.
And The Drivers?
For most drivers, moving to the AMD-64 is trivial. Here at OSR we’ve already ported several drivers to support AMD-64. All that’s required will be a careful read-through of the code to ensure 64-bit compliance (discussed below) and re-compiling using the 64-bit compiler provided as part of the DDK.....
.....Pure Dynamite
There’s no doubt about it: The AMD-64 is one incredible processor. It’s pure dynamite. Do your part by getting your drivers moved over to the AMD-64 now. Perhaps then you’ll be able to convince your boss that you need one of these babies for your desktop. I know an AMD-64 desktop is definitely in my future.
See the whole article at: osronline.com |
