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RAMBUS Memory Question
by chris

"I have a motherboard which takes RAMBUS memory. Is there some way I can use another type of cheaper memory in order to upgrade RAM?"
- Mohammed, Chicago, IL.

RAMBUS memory uses a serial addressing method, totally different from typical DDR or SDRAM technology. While there were expansion adapters for EDO and SDRAM memory modules, these memory module types all used a similar parallel addressing method. I have never seen anything that would convert between these different technologies.

A solution in the old ISA days was to add a memory expansion card to one of your system expansion slots. These expansion cards could be configured as LIM Expanded or Extended memory and were often the only way to increase the available RAM in older 286 and 386 systems. With current architecture, the memory slots are separate from the PCI expansion slots, so that the CPU can communicate at the maximum possible rate. With early RAMBUS memory, this is frequently at 400MHz per channel, allowing you to reach an impressive 800MHz transfer speed by taking advantage of two channels. Serial data access would normally be slower than parallel access if both were transferring data at the exact same rate. However, because of the very high clock speed of the RDRAM, early RAMBUS memory has data throughput capacity very close to current DDR-400 memory.

The cost of RAMBUS is generally high because of low demand, and most of the current (mainstream) system boards have all switched to DDR memory. Even if you could find a PCI memory expansion card or some sort of slot adapter, the cost of the card plus your memory would probably end up costing you more than just getting the equivalent RAMBUS modules. You also would take a huge performance hit when accessing memory in such a fashion. I would be very worried about possible timing issues that would show up in the form of system lock-ups, reboots, and random crashes.

My recommendation -- get RAMBUS modules or look for a system board that can use the inexpensive memory. Be aware that if you find a system board that can use your old CPU, the performance difference between DDR and RAMBUS will probably be slight, but still noticeably slower.

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