AMD64

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The AMD64 is a 64-bit processor architecture invented by AMD. It is a superset of the x86 architecture, which it natively supports.

Architecture overview

TODO: write about the AMD64 architecture. New instructions, capabilities, register sizes, etc.

NX Bit The NX Bit is a processor feature that prevents certain kinds of malicious software known as worms from taking control of a computer via a software attack known as a buffer overflow.

There are two versions of the A64 aside from the socket 754 (older) and socket 939 (newer). In addtion, the older versions of A64 use 130 nm transistors while the newest A64's use 90 nm transistors. Because of this AMD has been able to shrink the die size while still maintaining low heat output. One test has shown a 90 nm processor being overclocked to 1.45 times its stock speed.

Due to the larger width for address space, the AMD64 architecture can address up to 256 terabytes of memory. Future implementations of the AMD64 architecture may provide up to 2 exabytes of available memory.

Operating modes

Operating Mode		Operating System Required	Application Recompile Required	Default Address Size	Default Operand Size	Register Extensions	Typical GPR Width
Long Mode	64-bit Mode	New 64-bit OS	yes	64	32	yes	64
	Compatibility Mode		no	32		no	32
				16	16		16
Legacy Mode	Protected Mode	Legacy 32-bit OS	no	32	32	no	32
				16	16
	Virtual-8086 Mode			16	16		16
	Real Mode	Legacy 16-bit OS

AMD64 market analysis

AMD64 represents a break with AMD's past behavior of following Intel's standards, but follows Intel's earlier behavior of extending the x86 architecture, from the 16-bit 8086 to the 32-bit 80386 and beyond, without ever removing backwards compatibility. The AMD64 architecture extends the 32-bit x86 architecture (IA-32) by adding 64-bit registers, with full 32-bit and 16-bit compatibility modes for earlier software. Even the 64-bit mode is largely backward-compatible, allowing existing tools targeting x86 (eg. compilers) to be retargeted to AMD64 with minimal effort. The AMD64 architecture also features the NX bit.

Implementations

The following processors implement the AMD64 architecture:

AMD K8
- AMD Athlon 64
- AMD Athlon 64 FX
- AMD Opteron
AMD K9
- (dual core AMD K8 based processors)
EM64T
- Intel Xeon (some models)
- Intel Pentium 4 (some models)

External links

AMD's technical documentation for the AMD64 architecture (http://www.amd.com/us-en/Processors/DevelopWithAMD/0,,30_2252_875_7044,00.html)
Free AMD64 documentation on CD-ROM (US, Canada only), and download format (http://www.amd.com/us-en/Processors/ProductInformation/0,,30_118_4699_7980%5E875%5E4622,00.html)

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