Memory performance
Our first set of tests will highlight just how a faster bus and a new chipset can benefit the Athlon XP. We'll start out with SiSoft's Sandra memory bandwidth benchmark. This one uses extensive buffering, streaming SIMD extensions, nitrous oxide injectors, and rocket fuel to cram as much data as possible in and out of memory, so it will show us something close to theoretical peak memory throughput.

The Athlon XP 2800+ comes out looking amazing here, tying our DDR333-based Pentium 4 systems in a test customarily dominated by the Intel chips. You can see the increase of about 550MB/s over the 266MHz-bus Athlons. Both Athlons and P4s take PC2700 memory near its 2.7GB/s peak data rate. Our P4 test rig with PC1066 RDRAM comes out well ahead of all the DDR333 systems, but RDRAM isn't exactly a growth industry these days.

Cachemem gives us a bit of a different picture, because it's not so aggressive about pushing data through by whatever means necessary. Also, cachemem shows both read and write performance.

Here, the Athlon XP can't quite keep up with the P4 with its hyper-aggressive prefetching and larger L2 cache.

Now we'll look at memory access latency, which is every bit as important as bandwidth in the grand scheme of things.

Here's where the 333MHz bus really helps. It also doesn't hurt that we're running the DDR333 memory synchronous with the 333MHz front-side bus on the 2800+ system. All of the other systems here are running memory at a different base clock speed than their front-side busses.

Finally, we have Linpack, which shows us a nice picture of the cache and memory subsystems in our test systems. The size of the data matrix Linpack is processing increases from left to right, so the left side of the picture shows L1 cache at work, the middle shows L2 cache, and the right shows main memory access speeds. (Linpack also tests FPU performance to some degree, since it's crunching big floating-point numbers.)

This is about what we've come to expect from Athlons and P4s here, with one notable exception: the Athlon XP rig beats out all DDR333 systems above matrix sizes of about 1.2MB. This is new territory for the Athlon XP.

So initial indications are very positive for the 2800+ and its revamped memory subsystem. Let's see how these numbers translate into performance in real applications.