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 () REUs. Later, Commodore introduced a third model, for their Commodore 64 model: the 1764 () 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 ) 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. Hardware description Although the C128 could access more than of RAM through bank switching, the memory inside the REU could only be accessed by memory-transfers (STORE/LOAD/SWAP/COMPAREs) between the main memory and the REU memory. Additionally, the C128's built-in BASIC 7.0 had three statements, STASH, FETCH, and SWAP, for storing and retrieving data from the REU. Officially, only the 1700 and 1750 were supported on the C128. The model, the 1764, was released for the C64 at the same time. There were only minor differences between the three models. The original C64 power supply could not support the additional load presented by the 1764 so a 2.5 ampere C64 power supply was included. The 1700 uses sixteen 4164 64kx1 DRAM ICs, the 1764 has eight 41256 256kx1 DRAMs, and the 1750 has sixteen 41256 DRAMs. In practice, the difference between the 1764 and the earlier units had little effect on compatibility, and people used 1700s and 1750s successfully with the C64, and 1764s successfully with the C128, although the C64's stock power supply was