GeoRAM
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| GeoRAM | |
| Type: | RAM Expansion |
| Producer: | Shareware Plus |
| Price: | $50 |
| Released: | 2016 |
| Discontinued: | — |
| Processor: | |
| Memory: | 512 Kb |
| OS: | GEOS |
| Info: | Modern 100% compatible remake. |
GeoRAM is a 512KByte memory expansion for the C64 and C128 from the company Berkeley Softworks. It uses the registers at $dffe and $dfff to determine what part of the geoRAM memory should be mapped to $de00–$deff.
The register at $dfff selects which 16k block to map, and $dffe selects a 256-byte page in that block. Since there are only 64 × 256 byte pages inside of 16k, the value in $dffe ranges from 0–63. The number of 16k blocks that is available depends on the size of the GeoRAM:
| geoRAM Memory Blocks | ||
|---|---|---|
| RAM | 16 kB Blocks | Range |
| 512 kB | 0–31 | $00–$1f |
| 1024 kB | 0–63 | $00–$3f |
| 2048 kB | 0–127 | $00–$7f |
| 4096 kB | 0–255 | $00–$ff |
The two registers are write-only. Attempting to read them will only return random values. If you need to know the current values of the registers, you need to write a copy in normal RAM when you set them.
Clones
- BBG RAM by Performance Peripherals, a contemporary clone of GeoRAM with 1MB of RAM.
- GeoRAM by Shareware Plus, modern reverse engineered version of geoRAM.
Implementations
- 1541_Ultimate by Gideon Zweijtzer, an implementation of GeoRAM with size 128k to 16Mb. For 8 and 16Mb the 16k page is 32k and 64k. See forum link on size detection below.
References[edit | edit source]
- ↑ Robert Bixby: "The GEOS Column: Closeup on GEORAM", Compute!'s Gazette, Issue 83, Vol. 8, No. 5, May 1990, p 14
Links[edit | edit source]
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Wikipedia: GeoRAM |
