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| Clive Sinclair's ZX Spectrum home computer |
Many years ago I started Microlite by designing an external disk drive interface for the ZX Spectrum. The Spectrum was one of the first home gaming computers in the UK. The firm I was working for had a bunch of Quick-Disk drives gathering dust so hired me to design the interface.
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| Quick-Disk |
The Quick-Disk comprises a 2.8" floppy platter with a single spiral track rather like a record. To access data the drive traverses the whole track (48K-bytes) and this takes 8 seconds. You can turn the disk over to avail of a second 48K-bytes worth. The drive included a read/write head amplifier but no other processing.
The interface hardware was novel in that it used simple logic (TTL gates and registers) and the processing power of the Spectrum's Z80 microprocessor to decode or encode the drive data on the fly.
And then there was the necessary software. It was necessary to reverse engineer the Spectrum's operating system in order to integrate the disk drive and provide the necessary new commands to operate it. All this was done on a 80286 desktop running MSDOS - long before Windows or the internet. My best companion during this period of sheer hard graft was Dickens' Spectrum Advanced User Guide.
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| My best companion |
Thus I wrote a disk operating system or DOS. Others have made millions by so doing - I can't remember what I charged but it certainly did not make me rich, but it did kick-start my business and so I am eternally grateful to Clive, and to John my client, for the opportunity they gave me.
The final Clive Drive was technically a success. A mere 8 seconds to load a game was much better than many minutes with a cassette recorder and the interface supported hacking via the "Keymaster" button. But regrettably the product was not well advertised and was launched towards the end of the Spectrum's lifetime, so I doubt if my client ever recouped his costs.
Surprisingly the world still remembers the Clive Drive - so it wasn't all a dream after all! I found this picture and a couple of links here and here on the internet. The red button is the "Keymaster" button.
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| The Clive Drive interface and disk drive |
For those interested here are some photographs of circuit schematics and operating instructions which, I regret, I no longer have in digital format. Click on a picture to enlarge it.
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| First page of Clive Drive operating instructions |
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| Schematic page 1 |
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| Schematic page 2 - the disk drive connector is at the bottom with RDDT being the raw serial data from the read head, and WRDT the serial data to the write head. |
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| "Peek-Poker" used the Keymaster button to freeze a game and offer various debugging / hacking commands. |
