Moore's Law states that processing power will double every 18 months. And since the introduction of the Intel 8088 processor, this law has never been broken. But increasing the performance of a processor also requires increasing the bandwidth of the memory subsystem.

Here's a brief look at the past, present, and future memory technologies.

Fast Page - The standard type of memory for 486, and early Pentium 60/66/75/90 (still remember those?) systems. Back then, fast page memory was sufficient to keep up with the processor.

• EDO - Extended Data Output. EDO delivers about 10%-15% performance increase from fast page memory. The read cycle from memory and CPU is shorten. EDO became the dominant memory when the Pentium 100/133/150/166 (non-MMX) appeared on the market.

• SDRAM - Synchronous DRAM. With the advent of the Pentium MMX and Pentium II processors, memory technology took another leap in terms of raw speed. SDRAM coordinates the input and output of the memory and the processor. Makers of SDRAM claim a performance improvement of 50% or more over EDO memory. But in the real world, the performance is only about 20%. Currently, SDRAM is the dominant memory type, for both the 66MHz and the new 100MHz (PC100) bus.

• SDRAM II (DDR) - Double-data rate SDRAM aims to double the performance of current SDRAM. DDR allows the processor to read from memory on both the rising and falling edge of the clock. Currently, no Intel or third party chipset fully supports DDR.

• RDRAM - Rambus DRAM. This is based on the technology developed by Rambus, Inc. Intel have selected RDRAM for their future processors, IA-32 (Katmai) and beyond. RDRAM uses a narrow data channel clocked at extremely high speed to achieve high performance. The Nintendo 64 game console uses Rambus as its primarily memory interface.