Here's a quick blurb I got from Crucial:
Tracer memory is for hardcore gamers and modders - those who demand
top performing, stable memory, but who also appreciate the aesthetic
value of their hardware. To better meet the needs of this crowd,
weâ€™ve expanded the Tracer memory line to include 1GB DDR and DDR2
modules for enthusiasts sporting the newest technology.
The Crucial Ballistix Tracer memory line now includes the following
modules in densities of both 512MB and 1GB. Let the fraggin' begin!
- Crucial(R) Ballistix(TM) Tracer(TM) PC4000 (DDR 500)
- Crucial(R) Ballistix(TM) Tracer(TM) PC2-5300 (DDR2 667)