Editing Commodore REU (section)

==REU software support==
A small percentage of software made use of the REUs. Like other add-on products from [[Commodore International|Commodore]], their relatively small installed base relative to the huge number of C64s & C128s made software developers hesitant to invest much time and effort in supporting REUs. The lack of commercial support kept sales lower than they otherwise might have been. Due to its high speed relative to Commodore's floppy drives or even the commercially available hard drives, REUs did see support in the Commodore [[Bulletin board system|BBS]] community. Programs such as [[Bulletin board system#Color64|Color64]] required a REU to minimize load times when switching between sections of the BBS.<ref>{{Cite web|title = Color 64/v128 Preview Page|url = http://www.zimmers.net/bbs/c1bbs.html|website = Bo Zimmerman|access-date = 2018-11-12|language = en-US|last = Zimmerman}}</ref>

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 (8-bit operating system)|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 [[Bus (computing)|data bus]]&mdash;unlike the ordinary method, which had the computer's [[central processing unit|CPU]] do the transfer, thus spending at least three quarters of the bus capacity on [[fetch-execute cycle|instruction fetch]]es and only one quarter or less on payload data.