PC100 SDRAM: An Introduction

When SDRAM first started to pick up in popularity, around the time of the release of the Intel TX Chipset, maybe even a little later, reports quickly emerged of horror stories and incompatibility problems with certain types of SDRAM and motherboards. Not to mention the problems users experienced when pairing up two seemingly identical SDRAM DIMM modules. What became obvious to many users, as well as manufacturers was that a mutual standard for the manufacturing and mass production of SDRAM chips and Printed Circuit Boards (PCB's) had to be initiated. Unfortunately the cry for help was never loud enough for any action to be taken by the giants of the industry on behalf of the consumer, instead individual companies decided to develop their own standards and manufacture their SDRAM to the best of their ability.

The result of this lack of collaboration was the fact that matching a motherboard to the proper brand of SDRAM was another chore system builders would have to deal with in order to get the maximum stability out of their systems. In some cases the incompatibility problems were so extreme, motherboard manufacturers began shipping their own recommended brands of SDRAM with their motherboards, the classic example of this was MTech's Mustang R534F which was often bundled with at least 32MB of SMARTech SDRAM, or even the ASUS TX97 series which was bundled with ASUS' special 67MHz SDRAM DIMMs for quite some time.

The reason the industry giants, more specifically, the microprocessor industry giant, Intel, never stepped up to set a standard was because they were quite aware that a huge jump was about to be made in the memory bus speed the System RAM would have to operate at. Any standard Intel might have set would have simply been replaced by a more advanced standard in under a year, most likely angering the users that upgraded to the new standard of SDRAM only to realize that their DIMM's won't work with future motherboards. However, now, only weeks away from the official release of the BX Chipset, in addition to a number of Super7 chipsets that officially support the 100MHz Bus Frequency, are we beginning to see the first samples of what Intel's new standard of SDRAM, known as PC-100 (due to its ability to run at the 100MHz bus speed). Is the PC-100 SDRAM really worth it? Or are there other factors you must consider when purchasing PC-100 SDRAM modules?

The Specification

Corsair Microsystems, a popular manufacturer of DRAM's and PCB's was one of the first to announce a PC100 compliant SDRAM module. Not only did they make the announcement, they also managed to get quite a few engineering samples out into the public, somehow one of those samples managed to find its way into my testing lab, courtesy of New Frontiers Computers who will be carrying the modules upon their official release.

With the announcement of their PC100 SDRAM DIMM's, also known as BX Compatible Memory since they were designed mainly for use with the upcoming Intel BX motherboards and the 100MHz Bus Frequency officially supported by the BX Chipset, Corsair released a whitepaper document on the implementation issues of PC100 SDRAM, here are the specifications for PC100 SDRAM as described in the press release:

• Minimum and maximum trace lengths for all signals on the module
• Precise specifications for trace width and spacing
• 6 layer PCB's with unbroken power and ground planes
• Detailed specifications for the distances between each circuit board layer
• Precisely matched clock trace lengths, as well as routing, loading, and termination requirements
• Series termination resistors on the data lines
• Detailed SDRAM component specification
• Detailed EEPROM programming specification
• Special Marking Requirements
• ElectroMagnetic Interference Suppression
• Selectively gold plated printed circuit boards