The perpetual increases in microprocessor speed seem to have dropped off; the fastest Intel model can reach 3.06 GHz, but even with the appearance of the next processor, codenamed Prescott, only slight increases are expected. With RAM, it's a different story entirely: as things stand, manufacturers are outdoing themselves with increasingly faster memory chips and modules. Speeds of 433 or 466 MHz can be had today (PC3500 and PC3700), and give us hope of yet higher performance.

Two manufacturers sent us their current top-of-the-line models: TwinMOS sent us two 256 MB DIMMs designed for up to 466 MHz (PC3700). Buffalo Technology contributed to this test with two 512 MB DIMMs, also conceived with 466 MHz in mind. As usual with memory chips, these can also be easily operated at lower clock speeds.

Front Side Bus And Memory Clock

No two clock speeds are alike. Anyone who's had anything to do with processors, chipsets and main memory knows that there are various "areas" that can be clocked to operate at different speeds. One of these is the processor speed, also called the internal or CPU clock speed. The other is the Front Side Bus (FSB), which represents the link between the processor and the Northbridge. In today's Pentium 4, you'll find an FSB of 400, 533 or 800 MHz (achieved by transferring four bits per cycle per quad-data-rate based on an underlying clock speed of 100, 133 or 200 MHz), or 266 and 333 MHz with the Athlon XP (per double-data-rate with two bits per clock cycle based on 133 or 166 MHz).

Finally, the bus to the main memory is also a factor in overall performance. As a rule, performance assessment is geared to the latest in memory technology. In the past, the yardstick was the SDRAM with up to 133 MHz; nowadays it's Double-Data-Rate SDRAM with a limit of 200 MHz. With DDR, the effective performance is equal to the resultant effective clock speed of 400 MHz. Hence the DDR400 label - or PC3200, assuming a bandwidth of 3200 MB/s.