This little guide is to let people know some of the differances in computer DDR memory.

There are many differant type and makers of computer memory modules. Many of the manufactures of these memory modules use the same chips that are found on their compatitions modules, therefore name brand modules are not of much more quality than that of lesser known compaines, which means you can have a name brand and a generic brand in the same computer without any problems.

Even if a memory chip is compatible with your system doesn't mean it will always work. If you get one that doesn't work in you system, it may still work in another.

If you are looking for DDR memory (Double Data Rate) here are some things to remember.

1. Make sure that you are getting it with the right pin count.

2. DDR and DDR2 are not interchangeable. (for a desktop pc: DDR has 184 pins and DDR2 has 240 pins)

3. DDR-400 for example will only have a frequency of 200 not 400 if your system is not set up properly, most systems require you to have 2 modules in before your system will operate at DDR. Your system will not operate DDR with 1 or 3 modules in it. Because of this limitation it is better if you have 2 or 4 DDR modules in your system instead of one. For example 2 256MB modules will run faster than 1 512MB module

4. A 256MB PC-3200 DDR-400 184-pin Module for a PC is the same as the one for an iMac.

5. The Intel 875P, 865G, and 865PE chipsets have and architecture limitation as follows:

     *  Processors with a FSB-800 will support DDR-400

     *  Processors with a FSB-533 will support DDR-333 and DDR-266

     *  Processors with a FSB-400 will support DDR-266

     If your computer has one of these chipsets and you put DDR-400 memory modules in it, it is only going to run at DDR-266, therefore if your CPU only has a FSB of 400 (FSB-400) it should save you money if you use DDR-266 modules.

6. Watch out. There are many companies that charge you over $15 for standard shipping. Believe it or not USPS Priority Mail Flat rate boxes are half this price and if you can get 70 lbs in them it is still $7.70, if you use just a standard box by weight a memory module is less than $6.00, either way you get your item in 2-3 days after it ships.

7. Beware of crooks. There are people and companies the will sell an item for like $.99 with a $70.00 Shipping fee. This is against eBay's policies. These people are trying to get over on paying their selling fees. If you see any of these listings report them. It's sellers like these that make fees go up.

I hope this little bit of information helps.

Good Luck and Happy eBaying.