Operating modes

AMD Opteron processors use three different operating modes: 64-bit long mode, 64-bit compatibility mode, and 32-bit legacy mode. The 64-bit long mode requires a 64-bit OS and an application recompiled to use the 64-bit registers. In other words, the full capabilities of the expanded register set are available only when both the OS and the application support 64 bits. The 64-bit compatibility mode requires a 64-bit OS, but can use a 32-bit application. The additional registers are available to the OS, but not to the 32-bit application, because it cannot make use of them. When running in legacy mode, the processor acts just like a 32-bit processor, and the extra registers are not available (Table 2).

Table 2. Operating modes for AMD Opteron processors2

Mode

OS required

Application

Register extensions

GPR width

 

 

recompile required?

available?

(bits)

 

 

 

 

 

64-bit long mode

64-bit OS

Yes

Yes

64

 

 

 

 

 

64-bit compatibility

64-bit OS

No

Yes – to OS

32

mode

 

 

No – to application

 

 

 

 

 

 

 

 

 

 

32-bit legacy mode

32-bit OS

No

No

32

 

 

 

 

 

Memory addressability

The AMD Opteron registers are at least 64-bits wide. When operating in 64-bit long mode, the AMD Opteron processors support up to 48 bits (256 Terabytes) for physical memory and use 64 bits for virtual memory

Naming conventions

First-generation single-core AMD Opteron processors (Socket 940 and Socket 939) have three-digit model numbers in the form XZZ, and third-generation Quad-Core AMD Opteron processors (Socket F and Socket AM2) have four-digit model numbers XYZZ. AMD Opteron processor “generations” are called Revisions.

For all AMD Opteron processors, the first digit “X” specifies the number of CPUs on the target machine:

•1000 Series - Single-processor systems

•2000 Series - Dual-processor systems

•8000 Series - Systems with up to 8 processors

The second digit, Y, indicates socket generation, where “2” indicates Socket AM2 or Socket F (1207). Series 12ZZ processors are based on Socket AM2; Series 22ZZ and 82ZZ processors are based on Socket F (1207). If the second digit is “3,” it stands for third-generation AMD Opteron processors for Socket AM2 and Socket F (1207). If the second digit is “4,” it indicates Six-Core AMD Opteron processors.

2From the document titled “AMD64 Architecture Programmer’s Manual, Vol. 1: Application Programming,“ available at www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/24592.pdf

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