RETROSPECTIVE – the Microdrive (Sinclair Research, 1983)

Sinclair logo

As was usual for a Sinclair release there was great initial fanfare about their ‘revolutionary’ new storage media. Clive Sinclair claimed, upon release of the ZX Spectrum (23rd April, 1982) that their new ‘drives’ would ‘change the face of personal computing’ and ‘be cheaper than floppy disc drives’ (including the then emerging 3.5 inch format from Sony). Even the early ZX Spectrum adverts (1,2) mentioned the drives as ‘coming soon’. However, it was to be over a year and half before the drives eventually came to market; in what would prove to be the start of the end for Sinclair Research.. ..Microdrives became a byword for delay and disappointment.

In this retrospective were going to take an in depth look at Sinclair’s typically, atypical take on mass storage.. ..the controversial Microdrive.

ZX Microdrive

The ZX Microdrive

The start

The start was good. Initially, even the press were impressed, ‘Perhaps the biggest rabbit that Clive pulled out of his magician’s hat was the ZX Microdrive’, reported Popular Computing Weekly in their May issue. Sinclair lorded ‘This is a very tiny disk drive using two quarter-inch diskettes, with each diskette capable of holding 100KB, and a transfer rate of 16KB per second. You will be able to connect up to eight of these drives to the ZX Spectrum.. ..the price – £50’. This was, at the time, an amazing announcement.. ..Commodore’s single-disk 5.25 inch drive (a recently emerged industry standard format) for the VIC 20, which launched around the same time, was priced 8x higher! Even when Sony aggressively launched their new 3.5-inch discs and drives (November 1982 in the UK) they still cost £235. One of these newer storage formats went on to dominate and become a long standing industry standard, improved upon over time with higher storage capacities and faster read/write speeds.. ..the others did not!

Microdrive Cartridge

A Microdrive cartridge

To be fair, even in 1982 Sinclair acknowledged that the competing formats could store more data and were faster, but insisted that it was on the price point that the Microdrive would win.. ..’who needs such huge storage capacity anyway?’, Sinclair quipped. As 1982 ended, the adverts mentioning the Microdrive began to change.. ..initially the  word ‘microfloppy’ was quietly dropped. Then the 1982 release date changed to ‘early 1983’. As the New Year progressed, there was still no sign of the ‘wonder media’. Also rumours began to spread that the Microdrive wasn’t actually based on disk technology at all, but was tape based. It was the start of something that Sinclair would became infamous for.. ..promising way too much, way too early (in fact, they already had a bit of a reputation for this, as those who had ordered their famous ‘Black Watch’ already knew). Even the Advertising Standards Authority began to complain; they would later have a ‘field day’ with the disastrous launch of the Sinclair QL.

Initially, in July 1983 the drives started to ship, along with the ZX Interface 1 (3,4) required to link them to the ZX Spectrum. Sinclair also confirmed that each 43 x 30 x 5 mm Microdrive ‘cartridge’ contained not a disk but an infinite loop of tape – 2mm wide and claimed to be made of high-quality videotape, ‘not what you’d find in an ordinary audio cassette’. Apparently, Sinclair’s Microdrives were always intended to be based on tape technology.

During the Summer of 1974 a young engineer called Andrew Grillet, was interviewed for a job with Sinclair Research. According to Grillet, he was told that Sinclair was ‘going to build a computer’ and asked what ideas he might bring to the project. He proposed a data-storage system based on eight-track music cartridges, which were a popular precursor to the Compact Cassette. Thirty years later he was asked by The Register about his job interview at Sinclair Research.. ..he could not recall who he was interviewed by.. ..but he remembers they were impressed enough to offer him the job.. ..‘but Xerox offered me twice as much money, so I went to work for them’. In his 1985 book, The Sinclair Story, Rodney Dale, a one-time Sinclair Research employee, claims Sinclair product head, Jim Westwood and Chief Engineer, David Southward, jointly conceived the Microdrive in 1982. This would have been eight years after Grillet’s interview. Were these two men his interviewers? Had his idea remained hidden in the back of one or the other’s mind?

Sinclair were not the only company to recognise the value of looped tape storage. In 1979, California-based Exatron began pitching what it called the “Stringy Floppy” (5), a $250 device which took its own endless-tape cartridges, which Exatron called “Wafers”. Each wafer could hold 70KB of data on a loop of 1/60-inch tape. Both the Microdrive and the Stringy Floppy weren’t random access systems at all.. ..by moving the tape sufficiently quickly it was possible to make it appear to offer a kind of ‘pseudo random access’. At best the file you were seeking was just ahead of the read head’s position, at worst the device would have to spool right through the tape to reach the requested item.

Microdrive Cartridge Open

The inside of a Microdrive compared to a Compact Cassette

The problems

Like a lot of Sinclair releases there was a rush to production – initial Microdrives were actually released containing EPROMs, as there were still minor bugs in the control code. It quickly emerged that there were other problems too.. ..the drives were slow and repeated use could cause the very thin tape to stretch and fail.

Microdrive Care GuideEventually, the bugs were resolved, EPROMs became a thing of the past and the small addition of a 22 µF capacitor allowed the motor to more slowly come up to speed, causing less stress on the tape. Even so, users were advised by Sinclair to take care of their Microdrive cartridges and make back-ups.

Despite all of this, the initial reviews were generally positive, as at £49.95 the drives were considered reasonable. However, replacement cartridges, which cost £4.95 each, were not (they did later come down to a more sensible £1.99). Storage capacity though, initially stated at 100KB, had by launch become “no less than 85KB”. There were usage limitations as well.. ..each cartridge could only hold a maximum of 50 files, and data had to be read into memory, changed, the original erased and the new version written back to the tape. There was no way to modify the files directly, a consequence of the drive’s lack of true random access.

ZX Interface 1

The ZX Microdrive was connected via the ZX Interface 1

In addition, the Microdrive soon had competition, US company Astec introduced what it called the ‘Wafadrive’ (6) in the summer of 1984 – the product was sold in the UK by Rotronics – comprising of a dual-drive device which took 16KB, 64KB or 128KB tape cartridges (the drive mechanisms were made at the BSR factory in Stourbridge, which coincidentally my mum used to work at in the early 70’s). The drives were more expensive than Sinclair’s offering – £130 for the Spectrum version, or £160 for a unit that connected to the Commodore 64 – but the tapes were cheaper; just £3.95 for the highest capacity. The drives also had Centronics and RS232 ports on the back, similar to the ZX Inteface 1. Again, each cartridge contained a 5 M loop of tape to simulate random access. Sinclair User found the system to be rather more resilient than the Microdrive – mostly thanks to the larger, more robust tape cartridges – but slower. However Steve Gledhill, who runs a retro computer repair company, has found that over the subsequent 30 years Microdrive cartridges have tended to out-last Rotronics ‘wafers’. Neither of these formats found long-term success.

Rotronics Wafadrive

A Rotronics Wafadrive

For most users, it was simply due to the cost of the media.. ..microdrives were too expensive compared to using ordinary Compact Cassettes. In addition, very few software companies wanted to release via Microdrives (or indeed ‘wafers’) as: (i) the market was limited, (ii) mass duplication was difficult, (iii) reliability was an issue and (iv) the elevated costs of the cartridges, which were initially only available from their sole manufacturer, Sinclair Research.

Wafadrive and Microdrive

Comparison of the Rotronics ‘wafer’ and Microdrive cartridge

In 1984, the Sinclair QL was launched amidst much ‘fanfare’ (7). It was equipped with twin Microdrives (and no cassette interface), which were modified versions of the ones used for the ZX Spectrum.

The QL Microdrives ran 25% faster – this made duplication even more difficult, increased tape wear and reduced reliability.

According to Rodney Dale, who was working at Sinclair at the time, “the shipment of QLs was painfully slow, as each Microdrive cartridge was tested on its host machine to make sure that it worked properly”.

Rick Dickinson, Sinclair’s famous industrial designer laments the situation well.. ..’the Sinclair way of doing things meant that rather than re-design the Microdrive internals for the new computer, the Spectrum drives’ were simply put into the QL case’.. ..‘Failures of the Microdrive were really down to pushing production tolerances and materials too far, so variability came in’.

QL Microdrive Units

Inside the QL Microdrive units

In June 1984, even Popular Computing Weekly added to the fray, by using Microdrives in the QL, Sinclair is taking a risk that the machine may never receive proper software support. Anyone who writes a brilliant program for the QL cannot simply trot off to the nearest duplication plant, run off a few thousand copies and start selling them because Sinclair keeps sole control of Microdrive manufacture and duplication to itself’. They were right, neither the QL or the ZX Spectrum ever saw the volumes of Microdive sales that were required to secure the format… ..but by this time Sinclair had other issues.

The end

By 1985 Sinclair had suspended the production of the QL, in an attempt to save money – the company reporting a £18.3 million loss for the year to 31 March 1985. When Amstrad acquired Sinclair Research the following year (for a paltry £5 million), it promptly dropped the QL and the Microdrive platform. Amstrad had already launched their own the 3-inch diskette format (manufactured by Matsushita/Hitachi) on their PCW8256 word processor. They wanted their ‘new’ ZX Spectrums and CPCs to use this new format.. ..so that was the end of the Microdrive. Amstrad’s diskette would soon also join the Microdrive, as Sony’s 3.5-inch format went on to dominate, being used on the new 16-bit machines like the Commodore Amiga and the Atari ST as well as, of course, PC‘s and Mac‘s. Cassette storage passed into history too – although tape drives eventually found a niche in back-up systems, which didn’t require high access speed. The growing use and capacity of hard disks, combined with their falling prices would eventually limit even floppies to software installation and data exchange. Indeed, as we sit here in 2015 even optical formats are giving way to web based downloads, all being stored on the now ubiquitous hard disk or SSD.

A waste?

ZX Spectrum Expansion

The ZX Spectrum Expansion System

So was the Microdrive a complete waste of time?

Not all together.. ..it did for a short period offer Sinclair users a relatively cheap method of ‘mass storage’, particularly on the rare occasion when the company got its act together and created good value packs such as the ‘ZX Spectrum Expansion System’ (8).

However, it was the usual rush to market and over stretched promises which rather sealed its eventual fate, right from the very start. The design of the units was, as ever, beautiful.. ..they just needed to be a bit more practical and reliable. Many have berated Sinclair for the decisions he made and the fate of the company, but we should face facts.. ..the rising dominance of the PC and Microsoft was already well underway by the mid 80’s and was soon to ‘snowball’.. .. sitting here typing this on a modern PC, we all know where that story led.

Reference materials

(1) Early ZX Spectrum advert mentioning the ZX Microdrive; (2) Early ZX Spectrum brochure mentioning the ZX Microdrive; (3) ZX Microdrive and ZX Interface 1 advert; (4) ZX Microdrive and ZX Interface 1 information leaflet; (5) Exatron ‘Stringy Floppy’ advert; (6) Rotronics Wafadrive advert; (7) Sinclair QL information leaflet; (8) ZX Spectrum Expansion System information leaflet.


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