Intel 820 'Camino' Chipset

RDRAM was originally only specified to operate at the 400MHz frequency while transferring on both the rising and falling edges of the clock. However, it turned out that manufacturers were having problems producing reliable RDRAM at 400MHz, so they created two lower grade versions of RDRAM, operating at 356MHz and 300MHz.

Let’s first talk about how RDRAM frequency is assigned. The speed of your RDRAM is determined by your FSB setting using a multiplier. Currently the only multipliers we’ve been able to identify are the 2.0x, 2.5x, and 3.0x RDRAM multipliers. Intel seems to indicate in their preliminary documentation that a 2.75x and 4.0x setting is present but none of the boards we’ve looked at have offered either of those two options.

If your FSB is set to 133MHz then your possible RDRAM frequencies are 266MHz (133 x 2), 333MHz (133 x 2.5), and 400MHz (133 x 3). At the same time, we don’t refer to the different RDRAM frequencies by their clock speed, rather by 2X their clock speed. So 400MHz RDRAM would be considered 800MHz RDRAM, and 333MHz RDRAM would be considered 666MHz RDRAM and so on.

When you go out to buy RDRAM, you’ll be looking for one of three types that Intel has defined:

• PC800 RDRAM – operating frequency of 400MHz
• PC700 RDRAM – operating frequency of 356MHz
• PC600 RDRAM – operating frequency of 300MHz

An interesting feature most motherboards will allow is the ability to set the frequency of your RDRAM, so if you happen to have PC600 RDRAM that can work at PC700 speeds or PC700 RDRAM that can work at PC800 speeds then setting a few jumpers should accomplish that task.

RDRAM modules, otherwise known as Rambus Inline Memory Modules (RIMMs) look very much like SDRAM modules but will not fit into the same slots for obvious reasons. They do not have to be installed in pairs, but all empty RDRAM slots must be populated by a Continuity RIMM module, or a CRIMM for short. Most motherboards will ship with at least two of these modules depending on the number of RIMM slots on-board.

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Finally, due to their high operating frequency, don’t be surprised to see heatsinks on the modules themselves.

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The major downside to RDRAM (aside from the higher latency than SDRAM) is the pricing and the availability. If you thought the recent trend in SDRAM prices was insane, just wait until you begin seeing RDRAM available for sale online.

Industry analysts have been quoted as saying that the addition of an 820 based motherboard to a system (thus the addition of RDRAM) can add anywhere between $300 - $500 onto the end price of systems. While we have yet to see any 820 based systems ship yet, this initial pricing figure is quite frightening if it is any indication of the cost of implementation of RDRAM.

If RDRAM is to succeed, it has to drop in price to a reasonable level and it also must be able to be purchased by the masses. Currently, even vendors are having troubles getting RIMMs from manufacturers such as Samsung. It’ll be a while before they drop in price and increase in availability so don’t lose any sleep over waiting for that RDRAM shipment to hit anytime soon.