Finally the latest trend of the x86-processor arena has caught up with AMD's flagship the Athlon-processor as well. Since Intel had started to integrate 128 kB of second level cache onto the processor die of its Celeron processor (the good old 'Mendocino'-core) late 1998, one processor after the other followed this example. Number two was 'Dixon', Intel's mobile Pentium II CPU with 256 kB L2 cache, then AMD followed with the K6-3 which also sported 256 kB of on-die L2-cache. Finally, Intel launched the famous 'Coppermine'-core, which again uses 256 kB on-die L2-cache to make sure that Pentium III is able to compete with AMD's Athlon CPU. Now AMD followed suit and launched a new Athlon processor, coming with the highly anticipated 'Thunderbird' core.
On-Die Second Level Cache Makes the Difference
What's the big deal about an L2-cache that shares its silicon with the processor core? There are actually several big advantages that make this solution very attractive, but at the same time it's not quite that easy to implement.
On-Die L2-Cache Runs Faster
The first advantage of an L2-cache that is on the same silicon chip as the processor core is the fact that both parts can run at the same clock specifications. This means that the core and the second level cache clock frequency can be identical, making sure that the core doesn't have to wait a long time until the L2-cache delivers data. Before, when second level cache was found on external chips, it was only able to run at half or even less speed than the processor core. The worst scenario was or still is found in Athlon CPUs that run at 900, 950 or 1000 MHz, where the L2-cache is actually clocked at only a third of the core clock, forcing the processor core to wait up to 2 clock cycles until it can receive data from the L2-cache. The 3rd-party SRAM-makers simply couldn't supply L2-cache modules that would endure more than 400 MHz clock frequency, and so the great Giga-Athlon came so far with an L2-cache that is hardly faster than the L2-cache of an Athlon 800. On-die L2-cache is able to make sure that processors can still receive data from their L2-caches without much wait, even when they run at clock speeds way beyond 1 GHz.