RIMM

10/1/99

RIMM -- Small circuit boards used for Rambus memory. Similar in form factor to DIMMs used for SDRAM Memory. The acronym doesn't seem to be defined by anyone, but probably stands for Rambus Inline Memory Module.

RIMMS run at 2.5 volts are 133mm (5.25 inches) long and 32mm (1.25 inches) high. They carry a number of smaller Rambus modules. RIMMS may have either 168 or 184 pins. A "half size" (roughly -2.57in long, 1in high) 160 pin package called an SO-RIMM is also defined. Although the device has lots of pins, half of them are ground connections and most of the remainder are either address pins or unconnected. RIMMs are broadside addressed with the DRAM Row and column addresses being presented simultaneously on different pins. There are two nine bit data buses and a separate control interface.

Individual Rambus ("direct RDRAM") modules on a RIMM are 64Mb (for 8 bit RIMMs) or 72Mb for 9bit RIMMs. The number of Rambus modules may vary from 4 (32Mb RIMM) to 16 (128Mb). 9 bit RIMMs modules are used for ECC RIMMs, 8 bit for non-ECC. RIMMs using 128 or 144MBit Rambus modules are also defined. In all configurations, 32 logical banks are configured on the circuit board. Outputs are 16 data bits wide and may be clocked at 600, 711 or 800MHz with data transfers on both the rising and trailing edge of the clock. This can allow burst transfer rates of up to 3.2MByte/Second. Random access times for the first byte are on the order of 40 to 53 nSec.

RIMMs will indicate Capacity/number of Rambus modules e.g. 128MB/32. They will also indicate maximum speed and minimum Row Access Time. e.g. 800-40. The letters ECC will follow the size/number of modules if ECC is available.

High capacity RIMMs can draw nearly 3amperes at 2.5 volts = 7.5 watts for some operations. A heat spreader is used to distribute the heat generated over a large surface area.

Unlike DIMMS. SIMMs and similar older memory modules, unused RIMM sockets must contain terminator cards ("continuity modules") rather than being left empty.

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