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Question: My laptop uses PC66 SDRAM SODIMM's, can I use PC100/PC133 SODIMM's?

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This will depend on your laptop. With PC66 SDRAM based laptops things aren't as linear as with PC100 or PC133 laptops. The problem is that early PC66 SDRAM was 5V while PC100 and PC133 that followed in later years were all 3.3V. If your laptop dates back to the early production timeframe when PC66 SDRAM was only starting to appear in laptops then there is a very high chance it only supports 5V SDRAM. The notch on the SODIMM (the module or slot itself) determines whether it's 5V or 3.3V. Newer SDRAM based laptops use 3.3V SDRAM SODIMM's so it's both easy and possible to use PC133 SDRAM in a PC100 SDRAM based laptop.

Some PC66 SDRAM SODIMM's came as 3.3V, as a result some laptops used the 3.3V variant instead. If you own such a laptop then this is good news as in many cases you can simply use PC100 or PC133 SDRAM SODIMM's. The single aspect worth remembering is that the given PC100 or PC133 laptop memory module must contain PC66 information configured in its SPD chip for 100% successful operation.

Follow Method 1, Method 2 or Method 3 in part 5 of the Laptop Memory Upgrades Guide as this will help you determine what type SDRAM your laptop uses.

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...alternatively discover Where to buy 100% compatible SDRAM, DDR, DDR2 and DDR3 SODIMM memory.

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