The I/O Systems Graphics Board.

The I/O Systems Graphics Board appears to be a very attractive product – giving very high resolution at a reasonable price (384 dots by 224 dots by 55.00). It uses bit mapping and uses 10.5K of your memory when all the screen is displayed. The board does not contain any video memory itself, but is connected to a 16K block of the RAM (A) or (B) board.

What do you get ?

An assembled PCB 4.25″ x 3.75″, double sided but not plated through, with 6 socketed ICs, 3 resistors and 6 100n capacitors. There is also a 33 way low quality edge connector and a 35 page very high quality manual. Unfortunately there are no circuit diagrams and no real explanation of how it works.

Connection

This is the hard part. You have to lift several ICs on your precious Nascom and RAM board and make connections – 35 in all – with not very good instructions. It is quite difficult to know where to mount the board as it does not conveniently fit anywhere. Overall the board is not the easiest thing to connect or mount, but with some imagination it can be done.

Does it work ?

Very well, an extremely stable video with good clean lines. The result is better than with the original video as no accesses are made to write to the screen during the display refresh time. In fact the Z80 is shut down during the display refresh, which can be nearly 75% of the time, so don’t expect fast displays with this system as it is equivalent to running with a 1MHz clock (compared with an N2 at 4MHz).

Conclusions

The I/O Graphics Board is a clever implementation of a simple idea, possibly a little overpriced when the penalties are considered. The detractions are, considerable loss of system RAM, reduced operational speed of the system, and difficulty in performing a workmanlike job in connecting the card. I liked the manuals (with regard to programming the card) and the superb graphics that may be implemented. Overall, good, but really only applicable to dedicated graphics freaks.

The graphics card costs 55.00 and is available from:
I/O Systems Ltd.,
__, _______ ___,
Mill Hill,
London, ___ ___.

Classified Ads.

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