One of these AMD processors different than the others: AMD Athlon™ 64 processor, AMD Geode™ processor, AMD Opteron™ processor, AMD Sempron™ processor and AMD Turion™ 64 mobile technology Which one?

While each microprocessor family from Advanced Micro Devices is unique, four of them – the AMD Athlon 64, AMD Opteron, AMD Sempron and Turion 64 processors, are 32/64-bit chips that use the AMD64 instruction set. The Geode processor is an embedded chip that's 32-bit only. (And that's the last time we're going to discuss AMD Geode processors in this article.)

Now that we've got that out of the way, what differentiates those other chips? That's our mission in this article: to explore AMD's four 64-bit processor families, based on late-2006 specifications, to see where they're the same, how they vary, and where they are best deployed.

Most of the distinction between AMD's 64-bit chips, particularly the AMD Athlon 64 and AMD Sempron processors is subtle.

• The AMD Athlon 64 family of processors is for desktop PCs.
• The AMD Sempron processor is for entry-level desktops.
• The Mobile AMD Sempron processor is for notebook PCs.
• The AMD Opteron processor family is for servers and workstations.
• The Turion 64 mobile technology is for the mobile user and is for thin and light notebooks only.

Let's discuss the fundamental characteristics of these microprocessors, and then examine each of the processor families. Use Table 1 as a reference as we discuss the chips in more detail.

Instruction set: All of the chips here share the AMD64 Technology Core, specifically the x64 instruction set, which can either run standard 32-bit x86 software or 64-bit x86 software. When it's running a 64-bit operating system, it can execute both 32-bit and 64-bit applications simultaneously. The AMD64 core extends the classic x86 architecture to have eight new (16 total) 64-bit integer registers, eight new (16 total) 128-bit SSE/SSE2 registers, and support for advanced streaming instructions, such as SSE3.

Because all of AMD's 64-bit processors use the same instruction set, they are compatible with the same application software. What you'll find are varying performance characteristics, such as in the cores, cache and I/O bandwidth, as well as distinctive power profiles.

Cores: Some of these processors are currently available only in a single-core model. Others are available in single-core or dual-core models. Each core has a 64KB L1 instruction cache and a 64KB L1 data cache. The size of the L2 cache varies. The lower-power-consumption mobile processors have small, efficient 128KB, 256KB, 512KB, or 1MB L2 caches. The desktop processors have 256KB, 512KB or 1MB L2 caches for each core, which offer much better performance but draw more juice. The workstation/server AMD Opteron processors sport a 1MB cache for each core.

Direct Connect Architecture: All AMD64 processors have AMD's Direct Connect Architecture which can improve overall system performance and efficiency by eliminating traditional bottlenecks inherent in legacy architectures. Legacy front-side buses restrict and interrupt the flow of data. Slower data flow means slower system performance. Interrupted data flow means reduced system scalability. With Direct Connect Architecture, there are no front-side buses. Instead, the processors, memory controller and I/O are directly connected to the CPU and communicate at CPU speed.

Memory: All of these AMD processors also have an integrated memory controller. Some flavors of the chips are designed for cost-effective DDR SDRAM memory with a maximum bandwidth of 3.2GB/sec. All the newer models use the newer, higher-performance, more power-efficient DDR2 SDRAM memory, with a top bandwidth of 6.4GB/sec in some cases, or 10.6GB/sec for the latest AMD Opteron processors. Desktop AMD Athlon 64 processors, and the Next-Generation AMD Opteron processors use dual DDR2 buses with a maximum bandwidth of 12.8GB/sec. Multi-processor capable AMD Opteron processors also work with registered memory rather than the lower-cost unbuffered memory used by other AMD64 CPUs. Registered memory allows these AMD Opteron processors to use greater amounts of memory which is needed by some server and workstation applications.

HyperTransport technology: AMD uses HyperTransport bus, to link processors with the outside world. In the case of multi-processor servers and workstations, HyperTransport also links the processors with each other. (The AMD64 architecture, by the way, separates the memory bus from the I/O bus.) The AMD Athlon 64 and AMD Sempron processors and Turion 64 mobile technology each have a single HyperTransport bus link. The AMD Opteron processors come in two flavors: those with a single HyperTransport bus, for single-processor systems; and those with three HyperTransport links for dual-processor servers and workstations and large-scale enterprise servers with as many as eight processors.

Socket: As software developers, we generally don't need to worry about the physical sockets – but they're relevant in this case. There are several sockets currently in use by AMD: AM2, S1, 754 and 939 for the desktop and notebook processors, and 939, 940, AM2 and F (1207) for workstations and servers. The large 1207-pin Socket F (1207) is used for second-generation AMD Opteron processors with 1MB of L2 cache per core, DDR2 memory and three HyperTransport technology links. AMD refers to those as the "Next Generation AMD Opteron Processors" – more about those later. See Table 2 for a discussion of the sockets.

Power: Among the most significant variances between the four 64-bit processor families involves their power consumption. AMD Turion 64 mobile technology are the most power-efficient, as befits their intended use within small notebook computers. The AMD Sempron and AMD Athlon 64 processors are more similar, while at the high-end of the desktop market the AMD Athlon 64 FX family uses more power than the other desktop processors due to the high-end performance required for high-end multimedia and game PCs. Meanwhile, the AMD Opteron processor offers a range of power efficiency. There are extreme low-power versions of the chip, ideal for embedded applications, rackmount servers, as well as for blade servers; standard power versions for most typical servers and workstations; and higher-power versions that offer the highest performance for massively scalable HPC & workstation applications.

The AMD Athlon brand originally referred to a series of 32-bit x86 processors. As such, the company labels its newer AMD64-based AMD Athlon processors as AMD Athlon 64 processors. There are three different versions: AMD Athlon 64, which is for mainstream business desktops and large notebook PCs; AMD Athlon 64 FX, for high-end processors targeting multimedia and game PCs; and AMD Athlon 64 X2 Dual-Core, at the top level of consumer desktops. (A reference to the AMD Athlon 64 family can be found here.)

The single-core AMD Athlon 64 processors have clock speeds between 1.6 and 2.8 GHz. They draw between 35 and 89 watts, depending on their speed, and have L2 cache size of either 512KB or 1MB per core.

The single-core AMD Athlon 64 FX chips run at faster speeds of 2.2 to 2.8 GHz, and all have 1MB of L2 cache. They also draw more power, between 89 and 125 watts. There are microcode efficiencies within this chip that improve its math performance, making it better for gaming and simulation. They increasingly use DDR2 memory to improve performance; gaming is very memory-intensive.

The AMD Athlon 64 X2 dual-core processors have, well, two cores on one processor die. They run at 2.0 to 2.6 GHz, and have either 512KB or 1024KB of L2 cache per core. Despite this performance, they remain energy-efficient, with versions available from 35 to 110 watts.

The company spun the AMD Sempron processors out of its AMD Athlon family, to have a product for the mass market. The AMD Sempron processors are essentially lower-end AMD Athlon processor chips positioned against the Intel Celeron processors, with slower clock speeds and less L2 cache. Today, all AMD Sempron processors and most Mobile AMD Sempron processors are 64-bit compatible, Most AMD Sempron processors run at 62 watts, but there are some mobile models that run at 25 watts. Future models will run at 31 watts.

AMD offers both single-core and dual-core mobile processors in its low-power Turion 64 mobile technology. These chips draw between 31 and 35 watts, making them perfect for notebook and subnotebook computers. They have speeds of between 1.6GHz and 2.0GHz, and between 512KB and 1024KB per core. AMD refers to all these processors as Turion 64 X2 Dual-core for processors with 2 cores or Turion 64 mobile technology for single-core processors and they are positioned against Intel Centrino Duo mobile technology. They have significant power-savings features, both in the processors and in their special chipsets, for that market. To help keep power consumption down they use a 800MHz HyperTransport bus – slower than the HyperTransport bus used on AMD's other 64-bit processors.

AMD introduced the industry's first x86 64-bit processors with the launch of the AMD Opteron processors in April 2003. Today, AMD Opteron processors are found in everything from high-end enterprise servers to technical workstations to low-power embedded applications, and increasingly in blade servers.

The company currently offers single-core and dual-core AMD Opteron processors in dozens of varieties. Different models of the chip can have one or three HyperTransport technology bus links and because HyperTransport links can tie processors together, you can have AMD Opteron processor-based servers with as many as eight processors and 16 cores. L2 cache is 1MB per core regardless of the number of cores. Power consumption ranges from 30 watts to 125 watts per processor with "standard power" at 95W.

The newest chip on the block: AMD has recently introduced the Next-Generation AMD Opteron Processor. The original AMD Opteron processors used DDR1 memory; the Next-Generation processors use DDR2 memory, and include AMD's newest microprocessor features, such as AMD Virtualization (AMD-V) hardware-assisted support for virtualization. These processors, which use Socket F (1207) or Socket AM2, are designed to be plug-and-play swappable with AMD's forthcoming Quad-Core AMD Opteron processors, planned for release in 2007.

And as you'd expect, we'll be writing about all those things again soon – stand by for articles about the Next-Generation AMD Opteron Processor, improved power management, quad cores, and more.

Alan Zeichick is a technology consultant and analyst who focuses on software development and microprocessor technology. Reach him at zeichick@camdenassociates.com.