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The Bottom Line

Now that we have covered the basics of SDRAM technology, discussed the important timing factors involved in specifying SDRAM, and shown how they impact the parameters often bandied about by manufacturers and vendors, you should know exactly what you need in order to get the perfect SDRAM module. At least, in theory! The subject is both complex and confusing, and therefore a more specific "mini-FAQ" may be helpful in answering some of the more common questions regarding SDRAM module timing requirements:

• Do I need PC100 SDRAM for my system? If you have a 100 MHz system bus PC, yes. If you have a 66 MHz system bus, no. In theory, a non-PC100 module can be "pushed" to run in a 100 MHz system, but this is not guaranteed and may lead to system instability. (There is a PC100 specification for a reason!)
• Can I use PC100 SDRAM in a 66 MHz system? Yes.
• Will using PC100 SDRAM in a 66 MHz system make it run faster? No.
• I am still confused about "CAS2" and "CAS3" SDRAM. Which do I need? Is this something I need to pay attention to? Generally speaking, it is not something the average computer user needs to be concerned about. Those who overclock the system bus beyond 100 MHz may find more margin with CAS2 modules. Basically, get the CAS2 modules if the price difference is small, but don't overpay for CAS2 SDRAM. This distinction is extremely overplayed in the marketplace right now by vendors trying to make a fast buck by overstating the value of "CAS2".
• Is 3-2-2 SDRAM as good as 2-2-2? This is basically the same as the previous question, since the first number represents the CAS latency.
• If "CAS2" SDRAM is more likely to work in PCs with system bus speeds over 100 MHz, is paying extra for "CAS2" SDRAM a good investment in future upgradeability? Maybe, but probably not. Bear in mind that often technology takes unexpected twists and your "investment" could become moot very quickly. For example, two years ago a lot of people were buying "extra fast" EDO modules as an "investment" and well, that didn't turn out too well now did it?
• What is most important to consider when purchasing SDRAM modules? It's not the timing specifications, it's the company that is most important. You want to purchase from a reputable firm that can be trusted to sell what they say they are selling, that will stand behind the product, and that will remain in business to provide you with service if necessary. Make sure the memory has a full warranty, and that the modules are brand-named; they should have the name of the brand silkscreened onto the module or labeled with a sticker.

Dean Kent is the webmaster of Real World Technologies and a software engineer for Sterling Software's Storage Management Division. He has been involved in the computer industry for over 20 years, working with both hardware and software on mainframes, minicomputers and PCs. He recently closed his retail hardware business and is focusing his energies on hardware and software issues concerning IT professionals, and on current computer technologies. In addition to maintaining his own site, Dean rewrote the RAM guide on Tom's Hardware Guide.

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