Opteron is the AMD processor targeted to the server market. The first Opteron processors were based on AMD64 architecture (a.k.a. x86-64 or “hammer”), the same one used by other CPUs from AMD, like Athlon 64, Athlon 64 FX, Athlon 64 X2, Turion 64 and Sempron (socket 462 Sempron models aren’t based on this architecture, however). Most recent Opteron processors are based on the new AMD K10 microarchitecture. In this tutorial we will present Opteron’s main features and also several tables listing all models released to date.

The main feature of AMD64 and K10 architectures is the memory controller, which is embedded in the processor itself and not located on the chipset like all other CPUs.

Because of this architecture the communication between the CPU and the memory modules is done thru a dedicated memory bus, while the communication between the CPU and the chipset uses a separated bus, HyperTransport (click here to read our tutorial on HyperTransport).

There are two main differences between Opteron and other AMD processors.

First, some Opteron models can run in SMP (Symmetric Multiprocessing) mode, i.e. more than one processor installed on the motherboard, while other processors can’t.

Opteron CPUs are identified thru a “model number” and the first digit from this number indicates the symmetric multiprocessing level that the processor accepts: Opteron models starting with “1” can’t run in SMP mode, while models starting with “2” can run in a two-way SMP mode (i.e. up to two processors on the motherboard) and models starting with “8” can run up to an eight-way SMP mode (i.e. up to eight processors on the motherboard).

By the way, Opteron processors supporting DDR memories use a three-digit model number; these models are single- or dual-core processors. Opteron processors supporting DDR2 memories use a four-digit model number; these models are dual- or quad-core CPUs.

The second main difference is in the number of supported HyperTransport busses. All other CPUs based on AMD64 architecture and Opteron starting with “1” have only one HyperTransport bus. Opteron models starting with “2” have two HyperTransport busses (or three, on four-digit Opteron processors) while Opteron 8xx models starting with “8” have three HyperTransport busses.  

These aditional busses are used to interconnect processors when there is more than one processor on the motherboard. You can find a detailed explanation of this subject on our Inside AMD64 Architecture tutorial.

Opteron CPUs are available for several different socket types:

• Socket 939: There are some Opteron models from 1 series available for this socket. They are Athlon 64 or Athlon 64 X2 (if it has two cores) processors using a different name. These models work with standard DDR memories.
• Socket 940: These models require registered DDR memories (i.e. buffered modules), which are “special” memories targeted to servers.
• Socket AM2: There are some Opteron models from 1 series available for this socket. These models work with standard DDR2 memories.
• Socket F:  These models require registered DDR2 memories (i.e. buffered modules), which are “special” memories targeted to servers.

The first Opteron processors, which were launched for sockets 940 and 939, are called “First-Generation Opteron”. Opteron processors that use DDR2 memories and are based on AMD64 architecture are called “Second-Generation Opteron”. Finally Opteron processors based on the new K10 microarchitecture are called “Third-Generation Opteron”, and they also use DDR2 memories.

In all Opteron CPUs the memory controller works in dual channel mode, i.e. the memory is accessed using 128 bits, if two memory modules or an even number of memory modules are used.

Here is a summary of main Opteron features:

• Multiprocessing (SMP) support: up to two CPUs on models starting with “2” and up to eight CPUs on models starting with “8”. Models starting with “1” don’t support SMP.
• 64 KB instruction L1 memory cache and 64 KB data L1 memory cache.
• 512 KB (on third-generation Opteron processors) or 1 MB (on all other models) L2 memory cache per core.
• 2MB L3 memory cache on third-generation Opteron processors.
• HyperTransport bus running at 800 MHz (3.2 GB/s) or 1 GHz (4 GB/s). These clocks may also be referred as “1,600 MHz” or “2,000 MHz”, respectively.
• One HyperTransport bus on models from series 1, two HyperTransport busses on models from series 2 (or three busses on four-digit series 2 models) and three HyperTransport busses on models from series 8. 
• Dual channel configuration (you need to install two or an even number of memory modules to use this feature). 
• Addressing up to 1 TB (terabyte) of RAM memory (address bus with 40 addressing lines, 2^40 = 1 TB). 
• Support for MMX, 3Dnow!, SSE, SSE2, SSE3 (only on the latest models) and SSE4 (only on third-generation Opteron) instructions.
• EVP (Enhanced Virus Protection) Technology, also known as “NX Bit Disable”, read our tutorial on this subject. 
• AMD-V virtualization technology on four-digit models.
• Some models are dual- or quad-core. These models have two or four complete CPUs embedded together on the same body. Read our tutorials Dual Core AMD Processors and Inside AMD K10 Architecture to learn more about this technology.

Let’s see now all Opteron models released to date. As we have already explained, three-digit models are models that use DDR memories, while four-digit models are models that use DDR2 memories.