AMD K6-3

In February 1999 AMD announced that it had begun volume shipments of the 400MHz AMD K6-III processor, codenamed Sharptooth, and was sampling the 450MHz version to OEM customers. The key feature of this new processor was its innovative TriLevel Cache design.

Traditionally, PC processors have relied on two levels of cache:

  • Level 1 (L1) cache, which is usually located internally on the silicon
  • Level 2 (L2) cache, which can reside either externally on a motherboard or in a slot module, or internally in the form of an on-chip backside L2 cache.

In designing a cache subsystem, the general rule of thumb is that the larger and faster the cache, the better the performance (the more quickly the CPU core can access instructions and data). Recognising the benefits of a large and fast cache design in feeding ever more power-hungry PC applications, AMD’s TriLevel Cache introduced a number of cache design architectural innovations, designed to enhance the performance of PCs based on the Super7 platform:

  • An internal 256KB L2 write-back cache operating at the full speed of the AMD-K6-III processor and complementing the 64KB L1 cache, which was standard in all AMD-K6 family processors
  • A multiport internal cache design, enabling simultaneous 64-bit reads and writes to both the L1 cache and the L2 cache
  • A 4-way set associative L2 cache design enabling optimal data management and efficiency
  • A 100MHz frontside bus to a Super7 motherboard-resident external cache, scaleable from 512KB to 2048KB.

The AMD-K6-III processor’s multiport internal cache design enabled both the 64KB L1 cache and the 256KB L2 cache to perform simultaneous 64-bit read and write operations in a clock cycle. This multiport capability allowed data to be processed faster and more efficiently than non-ported designs. In addition to this multiport cache design, the AMD-K6-III processor core was able to access both L1 and L2 caches simultaneously, which further enhanced overall CPU throughput.

AMD claimed that with a fully-configured Level 3 cache, the K6-III had a 435% cache size advantage over a Pentium III and, consequently, a significant performance advantage. In the event it was to have a relatively short life in the desktop arena, being upstaged within a few months by AMD’s hugely successful Athlon processor.