Even though you have already run Everest software, it is always a good idea to visually check the type of SO-DIMM modules your notebook has as well as their speeds, since you need to buy a SO-DIMM memory module with the same technology and speed. In our case, our notebook had two DDR PC2700 256 MB modules from Samsung, so we bought a 1 GB PC2700 (“DDR333”) module.

click to enlarge
Figure 7: Checking the memory modules installed in our notebook

Below is a cross-reference table that may be useful.

Module Type	Chip Type	Technology	Clock
PC66	PC66	SDRAM	66 MHz
PC100	PC100	SDRAM	100 MHz
PC133	PC133	SDRAM	133 MHz
PC1600	DDR200	DDR-SDRAM	200 MHz
PC2100	DDR266	DDR-SDRAM	266 MHz
PC2700	DDR333	DDR-SDRAM	333 MHz
PC3200	DDR400	DDR-SDRAM	400 MHz

One interesting thing is that you can install modules with a higher speed grade than the one currently installed in your notebook. But if you must “mix” modules, it is ideal to have them all with the same speed grade. We could buy a DDR400 (PC3200) module for our notebook, but since we were willing to use one of the 256 MB original modules, which were DDR333 (PC2700), we bought a DDR333 (PC2700) module. We could buy and install a DDR400 (PC3200) module; it would have worked just fine.

When mixing modules with different speed grades, the system will access the modules at the slower speed available. For example, if we mixed our DDR333 module with a DDR400 part, the system would access the DDR400 part at 333 MHz even though this module could run faster because of the other module installed on the system. (This is a generic explanation; some systems can overcome this limitation.)