Expansion - C64 to 256kB

Posted on Feb 6, 2014

The inputs of the 74LS153 chip were mixed, which caused the address block decoding to fail. By now, I know of two Commodore 64 (mine and Pekka Pessi`s) where this expansion has been built, and of four Commodore 128s (of which two expanded by me, and the other two by Wolfgang Scherr and Matthias Kirchner from Germany). The expansion never became a success, although

Expansion - C64 to 256kB
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the banked concept is technically better than e. g. the Commodore REU. Meanwhile, there is one more program that supports the expansion: my transfer system prlink. Commodore 64 becomes remarkably more efficient by adding memory to it. Then the worst slow-down, incredibly slow disk drive, can be worked around by using a part of the memory as a RAM disk. In 1986, when the original article was written, there were no commercial memory extensions for sale in Finland. (Commodore`s RAM Expansion Units came to our market in the year 1987. ) Of course there were some in the USA, but they were quite useless, as they had only 64 ½kB of memory, and the price was high as well. When built by oneself, the following memory expansion should have costed 300-400 Finnish marks. One American dollar (USD) is equivalent to five or six Finnish marks (FIM). I constructed my expansion in 1993 March, and it costed 111 FIM. It could easily have been about 20 FIM cheaper. Many goals were set to the expansion. As many programs as possible should work also with it installed. This means that there could not be any radical changes to the memory map. The address space of an expanded machine really remains same for a usual programmer. After reset, the computer doesn`t differ from an unexpanded one practically at all. Even taking a look at the machine from outside doesn`t reveal the expansion, as Pekka needed the expansion port for his IEEE-488 interface...

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