<< Could someone please explain the different memory sticks please? I know about pc100, pc 133 whci are SDR, then there is pc 2100, 2400, and 2700, but I forget how they relate to 133, 266, etc. Thanks... >>
<< 2100 is 133 x 2, 2400 is unofficial 150x2, 2700 is official 166x2 >>
As hans007 mentioned, PC2100 runs at 133x2 = 266 MHz. So, you would expect PC266 memory sticks right? Well, yes and no.
The industry decided to change it's old naming convention of refering to the speed of memory. They new naming convention refers to the total bandwith (the maximum data transfer rate in MB/s). This was done after Intel decided to refer to RDRAM this same way (i.e. PC800). So, if you asked for PC266 DDR you would be getting the right product, but this product doesn't really exist, as the naming convention has changed. So you would need to ask for PC2100 instead.
This could be computed as 133.33... x 2 x 8 = 2133.33...... (they round off as part of the naming convention to yield PC2100) Breaking this down, "133" is the operating speed of the memory/bus (in MHz), "2"is the Double-Data Rate component (DDR SDRAM transfers info. on the rising and falling edges of the waveform; regular SDRAM transfers info. only on the rising edge of the waveform), and "8' is the size of the data path in Bytes.