REU (RAM Expansion Unit)
More info
- Creator
- Commodore
- Released
- 1985
- Type
- Memory expansion
- Models
- 1700, 1750, 1764
Commodore's external RAM module for the C64 and C128, with a DMA chip that shifts whole blocks between main and expansion memory without touching the CPU.
The REU arrived in 1985, first aimed at the C128 and GEOS. The cartridge holds not just memory — 128 KB in the 1700, 512 KB in the 1750, 256 KB in the 1764 — but a controller (the RAM Expansion Controller) that copies blocks between the computer's memory and the expansion almost instantly via DMA while the CPU sits idle.
GEOS used it as a lightning-fast RAM disk and swap area. The C64 scene later found the same muscle: streaming graphics and music, or storing precalculated tables that would never fit in 64 kilobytes. Modern cartridges and emulators mimic the REU with far more memory than the original.