The merits/weak points of the cache system

Asia Pacific Institute of Information Technology

According to these data Athlon's architecture is generally quite a bit 'mightier' than what the Intel competitor has to offer. Additionally the L1 caches are four times larger (two times 64 KByte instead of two times 16 KByte), so one could have expected the Athlon having even larger performance advantages over the Pentium III. The instruction cache is actually 92 KByte large because it also stores 'precoded' bits.

Similar to the Pentium III the L2 cache resides externally on the module and also runs at half the processor speed. But Athlon is more flexible and allows different L2 speeds from 1:1, 2:3, 1:2 and 1:3.

While in the Pentium III the cache controller sits as a separate component on the module, Athlon's version is integrated on the die. It supports caches from 512 KByte to 8 MByte that it controls with a distinct 72-bit backside bus: 64 Bit + 8 Bit for ECC (error correction). For the system Athlon uses a bus that optically looks just like a Slot 1 - but contains something totally different from a Pentium II bus (GTL+). AMD licensed the EV6 bus protocol of the Alpha 21264 from Digital that currently works with 64 Bit and 100 MHz on both edges of the clock (so-called DDR: Double Data Rate, which actually resembles 200 'classic' MHz). This way the bus that AMD also calls 'S2K' achieves a maximum transfer rate of 1,6 GByte/s, twice as fast as the current Intel competition. Later implementations should work with 133 MHz and finally 200 MHz and thus go up to 3,2 GByte/s.

· Outstanding sustained concurrency based on intelligent buffering of read/store data

· More information per read/store access based on quad-wide cache line(256 bits)

· Integrated, full-speed cache for lower latency on read/store access

· Increased maximum addressable physical system memory from 4 GB to 64 GB

Another thing in Pentium 3 is Advanced Transfer Cache is the enhanced on-die L2 cache for the Pentium III processor made possible by the transition to .18 micron process technology. Even though current Advanced Transfer Cache configurations have a smaller amount of cache as compared to 512kb of standard cache (256 instead of 512k), users will experience a performance benefit from Advanced Transfer Cache. Pentium III processors that utilize Advanced Transfer Cache are able to reference (or address) up to 64 gigabytes (GB) of main system memory while those that utilize Discrete Cache are able to reference up to 4 GB of main system memory . This full speed cache memory is wonderful as it gives better performance than if there were 512kb of normal cache memory .This cache memory uses a new more efficient algorithm named "8 way set associative". The Advanced Transfer Cache has the four primary features which leading to increased performance. The four features are as follows :