Re: 1 MB image for VIC-20

From: Marko Mäkelä (
Date: 2001-02-15 14:45:11

On Thu, 15 Feb 2001, MagerValp wrote:

> I haven't counted the number of Vic-20 ROMs out there, but in order to
> fit all of them in 1MB together with a menu program you'll probably
> have to compress them.

Yep, if you remove the duplicates archived on funet, you'll get around 1,4
megabytes.  When compressed with pucrunch, the whole lot takes about 8
kilobytes less than a megabyte.

> RB> Is there more info available, SW, HW, maybe site?

There's no documentation on this particular project available.  It's work
in progress.  The idea is to use a 1-megabyte ROM, maybe a MC 6821 PIA for
bank switching, and some glue logic.

Decompressing the games to RAM has the advantage that the hardware can be
made as simple as possible.  The 32k RAM can always be connected to
BLK[1235] and RAM[123] (the 3k expansion can share memory with BLK1).
Write accesses to BLK5 are routed to RAM; read accesses to RAM or to any
8k slice of the huge ROM.

If the games are stored as such on ROM, the bank switching logic would be
quite massive, since some games use only BLK5 while others use also BLK1,
BLK2 or BLK3.  But on the Atari VCS 2600, this would be the only feasible
approach, since it's too difficult to connect RAM to the cartridge port.

Also the PuCrunch decompressor can be simplified for this application,
since the input data cannot be overwritten by the output data, as is the
case with normal in-memory decompression.


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