Strange peripherals… memory expansions

Part 4 already in the “Strange peripherals…” series and this week, I’ll be looking at the so-called RAM Expansion Units or REU’s for short.
Originally, these units came out for the C128 in the following flavors: A 1700 unit sporting 128 KBytes of RAM and a 1750 with a whopping 512 KBytes.
Later on, the 1764 with 256 KBytes was released specifically for the C64.

The rarest of them all was the 1750 because of the RAM shortages of the late 80’s, but this was remedied later on when several firms provided upgrade kits for the 1700 and 1764 models to bring these also up to 512 KBytes (on the 1764 this was actually not even that hard, as it had the same mainboard as a 1750 unit, but only had 8 RAM chips instead of the 16 of the 1750.  So adding 8 more chips basically did the trick).
It became even possible in the beginning of the 90’s, to increase the capacity of to an impressive one megabyte and even higher!

Unfortunately, not much commercial software actually made use of the REU, although there was special software around to utilize the REU as a RAM disk, making it ideal for temporary storage of data.  But then again, switching of your computer also meant deleting all the data from the RAM disks memory.  If you remember my article on the Silicon Disk, you’ll know that type of disk with a base of 512 KBytes actually had a small battery inside to keep the data ‘alive’ after switching off the computer.

So, where did the REU as a RAM disk come in handy?  Well, the GEOS operating system had built in support for the REU as a RAM disk, as did the C128’s version of CP/M, so frequently used programs or modules could be loaded once in the RAM disk and then read back whenever needed, instead of being constantly read from the “slow” disk.
Some nifty disk copy programs used the REU to facilitate high-speed copying with a single disk drive, by loading data from one disk in memory and then allowing you to switch an empty disk and copying the data to it.
Furthermore, GEOS used the REU for quick memory transfers within the computer’s main memory to free up CPU cycles, making the machine run faster.

Technical savvy readers might argue that these REU’s did not really extend the base memory of the C64 or C128, so you didn’t actually end up with a C512 or something like that.  No, the REU was really to be regarded as “external RAM” only useable by applications that addressed the extra memory spaces (hence the use as a RAM disk).
This was in contrast to the REU’s for the VIC-20, which were RAM units that were directly available to the CPU itself and useable by BASIC.
It’s logical if you think about it, as the VIC-20 came standard with only 3.5 KBytes of RAM… not really much to go on if you want to do some serious computing stuff, so these units came in sizes ranging from 3 KBytes to 16 KBytes.  Not much by today’s standards of GBytes in a mere PC, but back then, it made all the difference.

The story however, does not end here… a couple of years ago, a company called Vesalia released cartridges like the MMC Replay which provided amongst others (like a very cool ability to hook up an RR-Net board so you could connect your C64 to the internet!!!) an REU of 512 KBytes, and the Chameleon cartridge, the biggest and baddest of them all, sporting all the features of the MMC Replay, but now backed with an REU of 16 MBytes!
Fans of the C64 made good use of these cartridges, resulting in a website actually being run on a C64:

Don’t rush of to the local electronics shop though as the cartridges are already long sold out due to their popularity – which Commodore geek wouldn’t want to run his own C64 webserver – but if you do happen to own one, and want to get rid of it, contact me!

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3 Responses to Strange peripherals… memory expansions

  1. There are new C64 cartridges available now that provide REU-compatible behaviour.
    For example,
    * The 1541 Ultimate provides 16MB REU as well as a number of other features such as MMC-like behaviour, USB device and SDRAM storage.
    * The 64NIC is RR-Net compatible:
    * The Chameleon will be available soon from Versalia and other retailers.

  2. Robby "The C= guy"

    Hi Marc,
    Thanks for the update. Sure look like excellent products and I like the compatibility with the RR-Net =)
    Good to see that the Chameleon will be back on sale… got a Retro Replay with an RR-Net some time ago of eBay.

  3. Pingback: HQ video playback on a C64 | A Commodore Geek's Blog

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