Home > Computers > Peripherals > Microdrive > The development of the Microdrive

By Ian Adamson and Richard Kennedy

The development of the Microdrive
(extracted from chapter 7)

In the months following its launch, one of the most frequently voiced complaints about the Spectrum was that it failed to provide users with an efficient method of storing data. Having written a program for the machine, the only way it could be saved for future use was with the aid of a cassette recorder and standard magnetic tape. Although cheap, the problem with cassette storage is that it is notoriously unreliable and impossibly slow. The most widely used alternative to cassettes is the floppy disc. Using a disc drive for the storage and retrieval of data is fast, efficient and reliable. It is also relatively expensive. A disc drive often costs more than the computer it serves.

At the Spectrum's launch, Sir Clive alerted his public to the fact that he was developing a new breed of fast-storage device, which he referred to as the ZX Microdrive. Since he offered no further details about the product, the world was driven to speculation. To the ever optimistic computer journalists, it seemed a fair bet that the man who smashed the price of the home computer was about to do the same for the disc drive.

Although the Microdrive was announced in April 1982, a number of Research employees seem to recall that work on the project was started around the time of the ZX81 development. What is not in question is that the solution to the design problems posed by the new product took considerably longer than anyone had anticipated. While David Southward ultimately assumed overall responsibility for the Microdrive, it seems only fair to note that it was the tenacity and imagination of R&D staffer Ben Cheese that got the product to the market.

The Microdrive is more of an upmarket cassette recorder than it is a low-grade disc drive. Sinclair's little black box is used in conjunction with especially manufactured miniature cartridges that contain a loop of 200 inches of magnetic video tape on which 85K of data can be stored. Although considerably slower and less flexible than a disc system, the Microdrive can nevertheless load a 48K program in about 4 seconds. As far as Spectrum users were concerned, its arrival made cassette storage an instant anachronism.

Whatever the merits or otherwise of the Microdrive concept, the device should go down in the annals of microcomputing as a minor miracle of engineering. The important point to bear in mind is that, even under ideal conditions, such a crude approach to fast-access data storage simply shouldn't work. Given the speeds at which it travels, the cartridge tape ought to snap and the virtually standard audio heads miss more data signals than they catch. In the light of the crippling component economies constraining the design, Cheese's achievement should be regarded as a work of genius.

According to frontline sources, progress on the Microdrive suffered from a curiously oscillating development. Engineers at Sinclair Research would, for example, complete the analogue part of the design, only to discover that their solution required prohibitively high component costs to get the digital end working. So they were forced to go back and modify the analogue design, and the process would start all over again. After a while, the entire Microdrive development took on the character of an endless loop.

Sixteen months after Sir Clive's original announcement, Ben Cheese's final design was at last immortalised on yet another Ferranti chip. The device was launched in July 1983 and retailed at £49.95. (One of the hidden drawbacks of the product was the high cost of cartridges, which initially sold at £4.95 each. In time, the tapes were reduced to the more realistic price of £1.95.) Given the incredible problems Cheese had overcome in the course of a gruelling three-year development, MD Nigel Searle's explanation of the Microdrive's delay sounds a touch churlish:

'The delay on the Microdrives has been the result of mechanical difficulties we had not foreseen. These have now been solved along with an improvement in the performance of the drives. They are now much more reliable than we had hoped to achieve... The designers would like to go on and on making improvements. But a line has now been drawn.'

(Microscope, 24 March 1983.)

In some respects, the launch of the Microdrive seemed to suggest that Sinclair Research was beginning to learn from its mistakes. The company made no attempt to pretend that initially the device would be produced in sufficient quantities to satisfy demand:

Sinclair's long-awaited Microdrive will not go on 'general release' even when it is eventually launched later in the year. Instead, only 5000 Microdrives will be made available to the original mail-order purchasers of the Spectrum ... Sinclair managing director Nigel Searle said this measure was being taken to 'reward' original Spectrum customers who suffered long delays as Sinclair struggled to meet demand. However Searle agreed that the exclusivity of the launch would also enable Sinclair to test demand for the Microdrives and gear production accordingly.


Although there was general disappointment that Sinclair had not attempted to come up with a cheap solution to industry-standard disc drives, the overall critical response to the Microdrives was positive:

In some ways [the Microdrive] could be more important than the Spectrum itself. That has done well because it is so cheap, not because it is technically special. The Microdrives on the other hand are very different to anything on the market and could start a whole new trend with other companies copying them. Let's all hope so.

(What Micro?, October 1983.)

Curiously enough, none of the initial spate of reviews predicted the most likely reaction from the software houses to a device using a non-standard medium like the Microdrive's cartridges. Indeed, some of the reviews anticipated that the software houses were likely to back Sir Clive all the way:

Sinclair seems to have done it again. The Microdrive should have a major impact on the Spectrum software market, not only for games but for sophisticated personal/business software like spreadsheets or database applications.

(Personal Computer News, 4 August 1983.)

As it turned out, the majority of software producers decided that by the time the Microdrive was launched the Spectrum was coming to the end of its commercial life. This, coupled with the high unit price of the cartridges, ensured that very little software was retailed for the Microdrive. In the final analysis, however, although the Microdrive was hardly a revolution in data storage, it was a massive improvement on cassette recorders.