RIMM

A RIMM is a narrow circuit board holding DRAM chips, designed to slot vertically into a Rambus memory controller on a motherboard. It was introduced in the late 1990s as a high-speed alternative to SDRAM, using the Rambus protocol to push data rates well beyond what parallel memory buses could achieve at the time. The form factor resembles a DIMM, but the pins and electrical interface are completely different, making RIMMs physically incompatible with standard memory slots.

RIMMs came in capacities from 64 MB to 1 GB, running at frequencies like 800 MHz or 1066 MHz, and required matched pairs called "Channel Rambus" on dual-channel motherboards. Intel backed Rambus technology early in the 2000s, particularly for high-end workstations and servers. Each RIMM carried 184 pins, and empty slots on the motherboard had to be filled with passive continuity modules, essentially dummy sticks that maintained signal integrity on the bus.

The architecture proved expensive to manufacture and license. Rambus charged per-unit royalties that drove up module costs relative to conventional SDRAM and later DDR memory, which offered comparable or better real-world performance without the licensing burden. Consumer uptake stalled, and even system builders who adopted Rambus early migrated back to standard DRAM within a few years.

RIMMs are now obsolete in new systems. Older Pentium 4 and Xeon machines from roughly 2002 to 2004 may still have them installed. The protocol itself survived in other forms, Rambus technology found broader adoption in graphics memory and embedded systems where the licensing model worked better, but RIMM as a consumer or server memory module form factor has been completely displaced by DDR, DDR2, and later standards.