SDRAM may be barred by crippling compatibility problems

IS managers who buy PCs today will be in for some memory-upgrade headaches down the road. Memory suppliers admit that synchronous DRAM (SDRAM) - the next-generation memory touted to solve the PC-memory bandwidth problem - will complicate and even jeopardise traditionally routine upgrades. What once were simple memory upgrades may now become major problems, as a lack of standards means users may have trouble finding compatible SDRAM memory modules. Worse, systems bought today may not adhere to tomorrow's standard.

IS managers who buy PCs today will be in for some memory-upgrade headaches down the road.

Memory suppliers admit that synchronous DRAM (SDRAM) - the next-generation memory touted to solve the PC-memory bandwidth problem - will complicate and even jeopardise traditionally routine upgrades.

For example, the problem will occur when IS managers look to bolster SDRAM-based systems, which are now hitting the market, with more memory to accommodate a new OS. Because of a lack of standards, users may have trouble finding compatible SDRAM memory modules. And even if memory-compatibility issues are ironed out, IS managers need to be aware that the systems they buy today may not adhere to tomorrow's standard.

The technical problem is that tighter timing requirements and the lack of a standard interface between the CPU and SDRAM memory can make it difficult, expensive, or even impossible to upgrade SDRAM-based systems, memory-industry executives say.

As a result, memory buyers will have to choose modules certified to run with a particular PC make and model. Unlike today's EDO DRAM, SDRAM may not be available in low-cost commodity packages.

Intel has championed the transition to 66-MHz SDRAM this year and 100-MHz SDRAM next year - and eventually to Direct Rambus DRAM - to increase PC performance for visual computing. (See "Rambus DRAM wins spot as Intel's memory technology," Dec. 16, 1996, page 9.)

But system OEMs can implement SDRAM main memory differently, says Bob Fusco, senior product marketing manager for memory products at Oki Semiconductor, in Sunnyvale, Calif. This means users will need different module types for systems from different vendors, and even different modules for newer machines from one PC company, he said.

One solution is for end-users to delay buying SDRAM systems.

"I'd wait until that's sorted out before I put my company at risk," Fusco says.

One problem is that some OEMs implement serial-presence detect and some do not. If a user plugs a memory module without the feature into a system that requires it, the system thinks there is no memory and won't even boot, Fusco says.

As a result, memory-module suppliers might have to manufacture different part numbers for different OEMs, which - as is the situation with today's notebooks - complicates buying compatible memory and increases cost.

In some cases, if a particular configuration proves not to be popular, an end-user may have only the system vendor as a source of upgrade DRAM. In an extreme case, an end-user could be left with no source of supply, Fusco says.

For now, third-party DIMM suppliers will tailor products for specific PC makes and models, which will be a headache for users who buy multiple models, says George Iwanyc, industry analyst at Dataquest.

"[Memory vendors] sell a solution for a particular machine," Iwanyc says. "If you have three or four different [PC] models, you might not be able to use the same DIMMs."

Compatibility will be an issue until the industry settles on an SDRAM DIMM standard, Iwanyc says.

Until then, PC buyers will have to be aware of the module type a particular system requires, says Jim Binford, DRAM commodity manager at American IC Exchange.

SDRAM modules "have to find a very specific home," Binford says. "They're not apples and apples."

For instance, Advantage Memory says that its modules are stable enough to work with systems that won't work with other modules, according to Steve Mood, director of engineering. The company has solved incompatibility problems in the IBM PC 300 GL series, Compaq Presario 4460ES, and other systems, he says.

"We have tested most other memory manufacturers' modules in both the Presario and PC 300 GL systems, and none of them have worked," Mood says.

For now, it is important that SDRAM modules be purchased from the larger suppliers, says Avo Kanadjian, vice president of memory marketing at Samsung Semiconductor, in San Jose.

The problem exists in the initial stage of the transition to SDRAM going on now and may recur with the switch to 100-MHz SDRAM next year, Kanadjian says.

The danger is that upgrades will not fit, sysd Bill Johnston, marketing vice president at Smart Modular Technologies. Vendors have to qualify SDRAM, especially 100-MHz SDRAM, to work with particular systems. Thus, end-users may have to go to the system OEM for upgrades, he adds.

Although the move to SDRAM has its pitfalls, vendors agree that the transition to Direct Rambus DRAM -- the successor to SDRAM -- should be easier because there is a well-defined interface that both system OEMs and aftermarket memory-module suppliers will accept.

Intel Corp., in Santa Clara, Calif., is at http://www.intel.com.

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