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512 KByte GEORAM Cartridge
GeoRAM is a 512KByte memory expansion for the C64 and C128 from the company Berkeley Softworks.
It is twice as high as a normal cartridge. In contrast to the REU this cartridge does not use DMA and blend pages of memory side in the first IO-area (start at $DE00). Which memory area is used, is controlled by a 5- and 6-bit register at the second IO-area (start at $DF00). One of the registers is at the even memory areas and the other one is at the odd memory areas.