My oldest daughter recently graduated from college and is going to Grad School in the fall. As a gift my wife and I bought her a new Mac laptop. She donated her old Compaq Prestige 2170 to my wife. In four years she has went through three hard drives in this laptop! I was installing some programs for my wife the other night and was shocked at how slow it was running. I checked and it was still using the original 256mb of memory that came with it. It is upgradeable to 1GB of RAM. I did a Crucial system scan and saw that it uses DDR PC2700 modules at 333mhz bus speed. It has two memory slots. I bought a 1GB PNY memory module which was on sale at Compusa. I removed the original 256 and installed the 1GB. The computer wouldn't boot. If I installed the 256 chip also it would boot, but the extra memory wasn't recognized in the BIOS. I assumed the 1gB had to reached by installing two 512mb modules so I exchanged the 1gb for two 512's. Same thing. The computer will not "see" the new modules. I contacted Compaq and they told me that I have to use PC2100 memory at 266mhz. The PC2700 should be 'backwards" compatible with slower 266mhz memory and in fact states this on the package. I contacted PNY and they said that only certain lots of modules are in fact compatible. On the module is a paper sticker with a lot number. Lot number "64WKD" is compatible. All the modules I purchased have lot # 64SND on them. Even though they say on the package that they will work for PC2100 applications! The PNY techie said that the module density is different. Just thought I would share this here with you all in case you have the same problem.