Commodore REU

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Commodore REU

Manufacturer	Commodore Business Machines (CBM)
Type	Memory expansion
Release date	1986; 38 years ago (1986)
Discontinued	1990; 34 years ago (1990)
CPU	MOS 8726 REC (RAM Expansion Controller) DMA ASIC
Memory	128 KB RAM (1700) 256 KB RAM (1764) 512 KB RAM (1750)
Storage	4164 64kx1 or 41256 256kx1 DRAM ICs

The Commodore RAM Expansion Unit (REU) is a range of external RAM add-ons.

At the time of introduction of the Commodore 128 home computer, two REUs were announced for that model; the 1700 (128 KB) and 1750 (512 KB) REUs. Later, Commodore introduced a third model, for their Commodore 64 model: the 1764 (256 KB)^[1]

The need for the REU came about when Commodore management decided to not use the final version of the custom Memory Management Unit (MMU) which then limited the size of memory in spite of early discussion of a larger memory map. Engineers traveling to the 1985 Consumer Electronics Show (CES) were confronted with flyers and billboards advertising a memory size that was no longer supported and finally the top management asked where the additional memory (up to 512 KB) would plug in.

By the time of the 1985 CES show in Chicago, the engineers were able to display a spinning globe of the earth as a demonstration of Direct Memory Access (DMA) by the new REU units.

The REU hardware was designed by Frank Palia and the dedicated RAM Expansion Controller (REC) integrated circuit (IC) was designed by Victor Andrade. Fred Bowen and Terry Ryan adapted the C128's KERNAL and BASIC to accommodate the REU natively and Hedley Davis wrote the globe spinning demo which was an impressive display of animation in the mid-1980s.