Commodore REU

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.

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.

Additionally, the C128's built-in BASIC 7.0 had three statements, STASH, FETCH, and SWAP, for storing and retrieving data from the REU.

The REU model 1750 can be modified to support up to 2MB on memory by installing 2 additional ICs for bank switch.

In the early 1990s, DIY modification schemes to increase the capacity of an REU to one megabyte or higher appeared on various online services.

The 1700 and 1750 had a resistor at position R4 that, according to Commodore engineer Fred Bowen, compensated for subtle timing differences in the expansion port on the C64 and C128.

To solve this, programmers wrote to, then read from, the REU's RAM to find out the amount of memory installed.

Additionally, many commercial programs simply overwrote the memory space occupied by the RAM disk software.

Official performance demonstration
1764 REU with Utility Disk and 2.5 ampere power supply