Surprise! Super Expander 64K secretly supports 256K

This is easily the best-bargain upgrade for anyone who inadvertently owns a Super Expander 64K card with only 64K installed.

Although the label only mentions 64K, the Super Expander 64K/80 Column card could be expanded to 256K by just moving a jumper and replacing its 4164 chips with 41256 chips.


It's a curiously subtle feature.

Contemporary advertisements from Nexo Distribution and Price Busters listed it as a 64K card, mentioning a 256K option like an afterthought.  Sometimes they also offered an RGB option.


For some reason, Nexo's inexpensive RAM cards usually bore a copyright "(C) OXEN" in the foil layer.  I don't know why...there wasn't any company called "Oxen" as far as I know.


Technical details as far as I know them:

  • The Super Expander 64K with 256K selects between 64K memory banks by writing 0, 1, 2, or 3 to address $C071.  This made it incompatible with some software that used address $C073 to select memory banks.  (Appleworks, for example, needed to be patched with Plusworks to access the additional memory banks.)
  • The RGB version of the Super Expander 64K could also switch between color and monochrome by setting or clearing the high bit at $C071.  (The RGB card has an additional jumper at the RGB port to select sync polarity.)
  • Locksmith's Fast Disk Copy natively supports the Super Expander 64K's additional memory when 256K chips are installed, making it possible to duplicate disks in a single pass.  Or use the "10" command to load an entire disk into RAM, then the "01" command to write an entire disk from RAM for mass-production.
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