Hardware Reference
In-Depth Information
Figure 3.37. AMD Athlon XP 0.13-micron processor for Socket A (PGA form factor).
Although the Slot A cartridge looks a lot like the Intel Slot 1, and the Socket A looks like Intel's
Socket 370, the pinouts are completely different and the AMD chips do not work in the same
motherboards as the Intel chips. This was by design because AMD was looking for ways to improve
its chip architecture and distance itself from Intel. Special blocked pins in either socket or slot design
prevent accidentally installing the chip in the wrong orientation or wrong slot. Socket A versions of
the Athlon closely resemble the Duron.
The Athlon was manufactured in speeds from 500MHz up to 1.4GHz and uses a 200MHz or 266MHz
processor (front-side) bus called the EV6 to connect to the motherboard North Bridge chip as well as
other processors. Licensed from Digital Equipment, the EV6 bus is the same as that used for the
Alpha 21264 processor, later owned by Compaq. The EV6 bus uses a clock speed of 100MHz or
133MHz but double-clocks the data, transferring data twice per cycle, for a cycling speed of 200MHz
or 266MHz. Because the bus is 8 bytes (64 bits) wide, this results in a throughput of 8 bytes times
200MHz/266MHz, which amounts to 1.6GBps or 2.1GBps. This bus is ideal for supporting PC1600
or PC2100 DDR memory, which also runs at those speeds. The AMD bus design eliminates a
potential bottleneck between the chipset and processor and enables more efficient transfers compared
to other processors. The use of the EV6 bus is one of the primary reasons the Athlon and Duron
(covered later) chips perform so well.
The Athlon has a large 128KB of L1 cache on the processor die and one-half, two-fifths, or one-third
core speed 512KB L2 cache in the cartridge in the older versions; 256KB of full-core speed cache in
Socket A Athlon and most Athlon XP models; and 512KB of full-core speed cache in later Athlon XP
models. All PGA Socket A versions have the full-speed cache. The Athlon also supports MMX and
the Enhanced 3DNow! instructions.
The initial production of the Athlon used 0.25-micron technology, with newer and faster versions
being made on 0.18-micron and 0.13-micron processes. Later versions were built using copper metal
technology, a first in the PC processor business.
In most benchmarks, the AMD Athlon is equal, if not superior, to the Intel Pentium III. AMD also beat
Intel to the 1GHz mark by introducing its 1GHz Athlon two days before Intel introduced the 1GHz
Pentium III.
