While recent systems use standard PC3200 DDR SDRAM or even faster DDR2 SDRAM at various speeds, several older high-end systems are still useful for today's applications. Intel's 850/850E chipset championed several years of P4 development, maintaining a significant upgrade market for RDRAM. The low-cost alternative to RDRAM should have been DDR SDRAM, but Intel initially punished the market with chipsets supporting just older PC133 SDRAM. During the same period, other chipset manufacturers applied PC2100 and PC2700 to their own products, supporting both AMD and Intel processors.
RDRAM (top) and DDR SDRAM (bottom) modules
First, the bad news. RDRAM prices have remained high in spite of drops in other products. Entire platforms are often abandoned during the upgrade process, when buyers find a low-cost CPU/motherboard/DDR SDRAM package that is cheaper than just what the RDRAM would cost. Such cost evaluations do not take into account labor, however, nor the possible need to replace the case and/or power supply. Such major changes are more favorable to home builders than corporate support staff.
The good news for retail motherboard owners is that PC3200 is backwards compatible to PC2700 and even PC2100 speeds. That's still no guarantee for owners of OEM manufactured systems, though, which often have BIOS limitations that prevent the use of memory with higher SPD values.
PC3200 DDR (top) and PC5300 DDR2 (bottom) modules
DDR2, featuring data rates up to 800 MHz, is slowly replacing PC3200 DDR SDRAM. Because of the wide range of available "standard" speeds, it becomes even more important to know what works with your system - and what it already contains - to avoid wasting money on a higher speed product than you'll use.
An extremely outdated PC133 SDRAM module
At the low end, PC133 prices seem reasonable only when its poor performance is ignored. We'll continue to reference Single Data Rate SDRAM throughout this article, but only for comparison's sake, as such systems are past due for replacement.