CAS Latency: Major Effect
The performance screw turned up a notch: CAS latency has a significant impact on the memory's performance.
It is not merely the memory clock (whether 100 MHz or 133 MHz) that governs the memory performance. Rather, it is the CAS latency that provides a key indicator as to how fast the memory can be accessed (latency!). Most older or cheap memory modules can often only be operated in CL3 mode (CAS latency = 3). These memories mostly do not feature an EEPROM chip, which is read out from the motherboard's BIOS. The EEPROM chip, which is found on every state-of-the-art memory module, is used for storing important data like CAS latency. Nevertheless, it is possible to access the memory with shorter latency cycles than the factory-defined ones. By way of illustration, it poses no problem for many CL3 modules (or CL 2.5 DDR-modules) to be operated with a CAS latency of 2. This operating mode does not work with all modules - trial and error is the only solution here.
The picture looks entirely different, however, if the BIOS reads out or interprets the data from the EEPROM incorrectly. In such cases, it can happen that a CL2 module (at 100 MHz or 133 MHz memory speed) is operated in CL3 mode, with the result that the performance drops by 5 percent or more.