Editing Commodore REU (section)

{{More citations needed|date=May 2023}}
{{Infobox information appliance
| image = File:PXL 20240301 183041629.jpg
| manufacturer = [[Commodore Business Machines]] (CBM)
| type = Memory expansion
| cpu = [[MOS Technology|MOS]] 8726 REC (RAM Expansion Controller) [[direct memory access|DMA]] [[ASIC]]
| memory = {{unbulleted list
  | {{nowrap|128 KB RAM}} (1700)
  | {{nowrap|256 KB RAM}} (1764)
  | {{nowrap|512 KB RAM}} (1750)
  }}
| storage = 4164 64kx1 or 41256 256kx1 DRAM ICs <!-- used "storage=" as "RAMtype=" is broken, puts text into "memory=" field. -->
| dimensions = 
| weight =
| releasedate = {{Start date and age|1986|}}
| discontinued = {{End date and age|1990|}}
| predecessor = 
| successor = 
| related =
| unitssold = 
| price = 
}}

The [[Commodore International|Commodore]] '''RAM Expansion Unit (REU)''' is a range of external [[random-access memory|RAM]] add-ons.

At the time of introduction of the [[Commodore 128]] [[home computer]], two REUs were announced for that model; the '''1700''' (128&nbsp;[[kilobyte|KB]]) and '''1750''' ({{nowrap|512 KB}}) REUs. Later, Commodore introduced a third model, for their [[Commodore 64]] model: the '''1764''' ({{nowrap|256 KB}})<ref>{{Cite web|title = Commodore 64 - The Best Selling Computer In History - Commodore Computers: VIC20 C64 PET C128 Plus4 - All 8 Bit Machines|url = http://www.commodore.ca/commodore-products/commodore-64-the-best-selling-computer-in-history/|website = Commodore Computers: VIC20 C64 PET C128 Plus4 - All 8 Bit Machines|access-date = 2016-02-08|language = en-US|last = Parallelus}}</ref>

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 {{nowrap|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|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.