AMD ATHLON

AMD with the Athlon processor have implemented a very advanced CPU design indeed. The feature list of the Athlon is very impressive as it includes features such as:

• 128 kb level 1 cache
• 200 MHz Alpha EV6 Front Side Bus
• 512 Kb to 8 Mb level 2 cache running from 1/3 to full clock speed
• Seven Issue Superscalar Architechture
• A Fully Pipelined (Superscalar?) FPU
• 19 New 3DNow! Instructions
• AGP 4X support (not with AMD 750 chipset, thus not available at launch)
• UDMA 66 support native to chipset
• Slot A motherboard interface (similar to Intel’s Slot 1)
• Support for PC-100 & PC-133 SDRAM, DDR RAM & possibly Rambus in the future.

These features allow the Athlon a number of advantages over existing x86 CPU designs, thus making it the first 7th generation x86 processor. What we can see is that the increase in level 1 cache to 128 Kb could potentially bring performance benefits to a wide range of applications, especially when the chip is used in a multi-processing envioronment. This coupled to a flexible level 2 cache arrangement, which allows AMD to tailor the Athlon to particular markets by fitting it in different amounts and speeds. This gives AMD the ability to produce a range of Athlon’s similar to Intel’s P6 line with a range as broadly similar to the Celeron to Xeon line up.

Most dramatically, the Athlon features a fully pipelined Floating Point Unit thus allowing AMD to redress the deficiency in FPU performance that their CPU’s encountered when compared to Intel offerings. Instead the Athlon offers PC users the first CPU which has a separate pipeline for FADD, FMUL and FSTOR instructions, unlike Intel’s P6 which only offers 1 full pipeline and another shared pipeline. This has allowed the Athlon to gain some very impressive benchmark scores in numerous 3D games and applications on the merit of its FPU’s sheer strength.

The Athlon also features a very advanced core, which features a 2048-entry branch prediction table, which stores the most commonly used instructions and attempts to predict the next operation. As the Athlon features shorter pipelines when compared to the P6 core, the penalty for a missed prediction is smaller.

AMD have not rested on their laurels as far as their 3DNow! Instruction set is concerned. With the Athlon, we see the 21 3DNow! Instructions being enhanced by a further 19 new instructions. Many of these offer the same prefetching functions that Intel’s SSE instructions use. The enhanced 3DNow! will be supported by DirectX 6.2.