RAM Guide

So What's in Style?

Aside from sizes, there are many different "styles" of RAM, classified according to their mode of data transfer. A few years ago, the most common type of RAM was called Fast Page Mode or FPM DRAM. We have come to refer to FPM RAM as "normal" or "non-EDO" DRAM. FPM DRAM gets its name, from the mode by which it transfers data, via a type of transfer style called Fast Paging. For most users, FPM DRAM was sufficient, and it pushed the access time down to an amazing 60ns! Although, Fast Page Mode DRAM was more than enough for the 486 class of systems, Pentium users demanded more. Once again the market responded by implementing a new type of transfer technology, called Extended Data Out Transfer Mode, or EDO for short. EDO has been popular ever since it was first introduced, mainly because of its superb performance and relatively low cost however its compatibility with nearly every system made it a very popular choice among new system builders. The highest quality EDO DRAM pushed the access time barrier down to 45ns, and thoroughly satisfied Pentium as well as Pentium Pro/II users. An even faster type of EDO DRAM was developed originally for use with the Intel 82430HX chipset, which was Intel's first chipset to support it. That type of DRAM boasted greater performance than EDO, mainly because it could transfer in bursts, much like cache, hence the name Burst Extended Data Out DRAM or BEDO DRAM. So why are we moving away from EDO and BEDO? With higher clock speeds, we require higher memory bus speeds to compensate, otherwise we would have extremely high clock multipliers with our bus speeds holding us back. Officially, EDO and BEDO DRAM is only spec'd for Bus Speeds up to 66MHz, however people have been able to use the 75 and 83.3MHz bus speeds successfully with EDO DRAM, so a faster type of RAM is still not "required" but one would be nice...that's why SDRAM was created. SDRAM, short for Synchronous transfer Dynamic Random Access Memory, transfers data synchronously instead of the old asynchronous methods used with FPM, EDO, and BEDO. Although SDRAM pushed the access times down to a meager 10ns (!!!) lack of proper support by a chipset caused it to perform only a tad better than EDO. The only reason people have for purchasing SDRAM over EDO is that SDRAM is spec'd for bus speeds up to 100MHz, and most likely can operate at speeds much higher. Their official support for bus speeds in excess of 83MHz makes SDRAM a more stable solution when overclocking, and therefore makes SDRAM the ideal choice...or does it?

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How much are you really willing to pay for a stable system? This is where the ongoing "Generic vs Brand Name" debate comes into play. Generic EDO is usually stable enough for most systems, and sometimes works flawlessly at 75 and 83MHz bus speeds with a little tweaking of your BIOS Timings. However, problems can be experienced when you are using SDRAM, especially in pairs. Some modules simply don't work with some motherboards, and work perfectly fine with others. Since SDRAM is not yet a standardized technology, manufacturers sometimes manufacture poor quality modules, that although work perfectly in single modules (courtesy of their DIMM packaging) fail to function in pairs. It is for that reason that many motherboard manufacturers are packaging SDRAM with their motherboards that have been completely tested when using both single and multiple modules. Currently, chips (not modules) made by NEC are the most compatible, however Toshiba, Micron, and SmarTech (all of which DO NOT use NEC chips) manufacture SDRAM which has a very high compatibility rate. As far as EDO is concerned, Micron EDO is considered the best and most stable, with Toshiba as well as some other manufacturers close behind. With EDO however you can feel much safer when using generic modules than when using generic SDRAM since EDO has been around for much longer. In time we'll see generic SDRAM improve in quality, but that will take action by one company to set the standard in quality SDRAM. Basically, with system memory, you get what you pay for. I personally use Micron EDO for all of my tests involving EDO DRAM, and I use Advanced Megatrends SDRAM for my SDRAM tests unless otherwise specified by the motherboard manufacturer.

Here's a small chart to help you decipher those pesky little ID numbers on chips. Below are manufacturer's ID Strings which can be found on the invidual chips of your RAM modules. If you have any more to add to this list please email me.