even the commercially available hard drives, REUs did see support in the Commodore BBS community. Programs such as Color64 required a REU to minimize load times when switching between sections of the BBS. The REUs came with software to use the extra memory as a RAM disk, but the RAM disk's compatibility with commercial software varied as some commercial software relied heavily on various quirks of the Commodore 1541 floppy drive. Additionally, many commercial programs simply overwrote the memory space occupied by the RAM disk software. The GEOS operating system had built in support for the REU as a RAM disk, as did the C128's version of CP/M, and some disk copy programs used the REU to facilitate high-speed copying with a single disk drive. GEOS as well as other programs even used the REU for quick memory transfers within the host machine's main memory by storing a memory block into the REU and then fetching it back to another location. Using this method, only the actual data to be transferred needed to travel on the machine's data bus—unlike the ordinary method, which had the computer's CPU do the transfer, thus spending at least three quarters of the bus capacity on instruction fetches and only one quarter or less on payload data. See also Super 1750 Clone geoRAM Creative Micro Designs RAMLink Creative Micro Designs 2 MB REU, (1750 XL) References External links REU Games & Utilities REU Programming documentation Source code of RAMDOS, a RAM disk program for the Commodore RAM Expansion Unit REU Programming - by Robin Harbron Memory expansion REU Home computer peripherals Commodore 64