Synchronous Dynamic RAM, or SDRAM is a type of RAM that is stored on DIMMS and synchronized with the system clock. SDRAM runs at the same speed as the system bus. DIMMs (Dual Inline Memory Module) are 168-pin modules that take full advantage of the 64-bit architecture of Pentium and Power Macintosh systems and can be installed as a single stick.

A newer faster DIMM model is quickly dominating the RAM market. It's called DDR Ram, or Double Data Rate. It's a type of SDRAM that delivers data at double the rate for a given clock frequency. The bandwidth in a PC of DDR PC266 parts with 64-bit bus using a 133MHz clock is over 2 GBytes/second. Soon, all new computers will be designed to accept DDR DIMMs.

Unfortunately, 72-pin SIMMs won't fit into DIMM slots on the inside of the computer. However, special converters may allow 72-pin modules to be used in 168-pin ports. This is a short-term solution at best.

DIMM technology is quickly beginning to dominate the market in the short term. SIMMs are becoming more difficult to find, and when you do find them, they are usually priced far over the cost of a SDRAM DIMM.

The other major memory development is "non-volatile RAM." This technology allows RAM to hold some information in its memory, even after the computer's power is turned off. Right now, non-volatile RAM is used most often in expansion cards for laptops, but you can expect it to cross over into desktop machines, and to drop in price and increase in speed.