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Commodore's RAM Expansion Unit (REU) range of external RAM add-ons for their Commodore 64/128 home computers was announced at the same time as the C128. The REUs came in three models, initially the 1700 (128 KB) and 1750 (), and later the 1764 (, for the C64). 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 CES show were confronted with flyers and billboards advertising a memory size that was no longer supported and finally the most upper management asked where the additional memory (Up to 512K) 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 Integrated Circuit (IC) was designed by Victor Andrade. Fred Bowen and Terry Ryan adapted the kernel 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, thus, giving an equivalent to a (slow) small memory window. 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. However, aside from a bundled 2.5 ampere C64 power supply unit (the factory unit could not support the 1764), there were only minor differences between the three models. 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 inadequate to reliably handle the power load of any of them. Some dealers unbundled the 1764 and the power supply in order to sell the power supply to C64 users, and/or upgrade the 1764 to . Because of memory chip shortages in the late 1980s, the 1750 was only produced in small quantities. However it was not difficult to upgrade a 1700 or 1764 to . Several firms did this commercially, either selling upgraded units or upgrading customer-supplied units. In the early 1990s, DIY modification schemes to increase the capacity of an REU to one megabyte or higher appeared on various online services. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Commodore REU」の詳細全文を読む スポンサード リンク
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