ZX Microdrive
Encyclopedia
Magnetic tape data storage
Magnetic tape data storage uses digital recording on to magnetic tape to store digital information. Modern magnetic tape is most commonly packaged in cartridges and cassettes. The device that performs actual writing or reading of data is a tape drive...
system launched in July 1983 by Sinclair Research for their ZX Spectrum
ZX Spectrum
The ZX Spectrum is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research Ltd...
home computer
Home computer
Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...
. The Microdrive technology was later also used in the Sinclair QL
Sinclair QL
The Sinclair QL , was a personal computer launched by Sinclair Research in 1984, as the successor to the Sinclair ZX Spectrum...
and ICL One Per Desk
One Per Desk
The One Per Desk, or OPD, was an innovative hybrid personal computer/telecommunications terminal based on the hardware of the Sinclair QL. The One Per Desk was built by International Computers Limited and launched in the UK in 1984...
personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
s.
Development
It is claimed the Microdrive was originally proposed by Andrew Grillet at an interview with Sinclair Research for what was to become the ZX81. Grillet proposed "a version of the Learjet Stereo 8 system, modified to allow two 64k core images per track for roll-out roll-in swapping using the KUTSKansas City standard
The Kansas City Standard , or Byte standard, is a digital data format for audio cassette drives. Byte magazine sponsored a symposium in November 1975 in Kansas City, Missouri to develop a standard for storage of digital computer data on inexpensive consumer quality cassettes, at a time when...
protocol". The ZX81 had only 1k of RAM. Mr Grillet was offered better pay by Xerox Corporation, and never worked on the ZX81 or the Spectrum. The primary engineer involved in the development of the Microdrive was Ben Cheese
Ben Cheese
Ben Cheese was the engineer who got Sinclair's ZX Microdrives to work. Authors Ian Adamson and Richard Kennedy, in their book Sinclair and the "Sunrise" Technology, writes that "it seems only fair to note that it was the tenacity and imagination of R&D staffer Ben Cheese that got the product...
.
Products
Typically of Sinclair Research, the ZX Microdrive was comparatively cheap (£49.95 at launch) and technologically innovative but also rather limited. Connecting a ZX Microdrive to a ZX Spectrum required the ZX Interface 1ZX Interface 1
A peripheral from Sinclair Research for its ZX Spectrum home computer, the ZX Interface 1 was launched in 1983. Originally intended as a local area network interface for use in school classrooms, it was revised before launch to also act as the controller for up to eight ZX Microdrive high-speed...
unit - which cost £49.95 - although this could be bought packaged with a Microdrive for £79.95. Later, in March 1985, the ZX Spectrum Expansion System was launched for £99.95. This consisted of Interface 1, a Microdrive, a blank cartridge and several cartridges with content: the Tasword Two
Tasword
Tasword is a word processor for the ZX Spectrum developed by Tasman Software. The first version was released in 1982 and spawned two major revisions in addition to several add-ons and, later, tailored versions for the +2 and +3 Spectrum models, the SAM Coupé and the Amstrad CPC range...
word processor
Word processing
Word processing is the creation of documents using a word processor. It can also refer to advanced shorthand techniques, sometimes used in specialized contexts with a specially modified typewriter.-External links:...
plus Masterfile filing system
Database
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
, Quicksilva
Quicksilva
Quicksilva was a British games software publisher active during the early 1980s.Amongst the company's successes were Jeff Minter's Gridrunner and Bugaboo , a title licenced from Spanish software house Indescomp S.A....
's Games Designer and Ant Attack game, and an introductory cartridge. A total of eight ZX Microdrive units could be connected to the Interface 1 by daisy chain
Daisy chain
Daisy chain may refer to a daisy garland created from daisy flowers, the original meaning and the one from which the following derive by analogy:*Daisy chain *Daisy chain *Daisy chain...
ing one drive to the next via an electrical connector block.
Technology
Microdrives used tiny (44 × 34 × 8 mm including protective cover) cartridges containing a 5 m (200 inch) endless loop of magnetic tape, 1.9 mm wide, driven at 76 cm/second (30 in/second); thus performing a complete circuit in approximately 8 seconds. The cartridges held a minimum of 85 kBKilobyte
The kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
when formatted on a ZX Microdrive (exact capacity depended on the number of "bad" sectors found and the precise speed of the Microdrive motor when formatting). The data retrieval rate was 15 kB/s (i.e., 120 kbit/s). It is possible to 'expand' the capacity of a fresh microdrive cartridge by formatting it several times. This causes the tape to stretch slightly, increasing the length of the tape loop so that more sectors can be marked out on it. This procedure was widely documented in the Sinclair community magazines of the 1980s.
Unfortunately, the system acquired a reputation for unreliability. The tapes stretched during use (giving them a short life span) eventually rendering the data stored unreadable. Also the "write protection" was software based so that a computer crash could erase the data on an entire tape in 8 seconds. The cartridges were relatively expensive (initially sold for £4.95 each, later reduced to £1.99). Similar technology was used in other devices, such as the Rotronics Wafadrive
Rotronics Wafadrive
The Rotronics Wafadrive was a peripheral for the Sinclair ZX Spectrum home computer, intended to compete with Sinclair's ZX Interface 1 and ZX Microdrive....
, and was sometimes known as a "stringy floppy
Stringy floppy
The Exatron Stringy Floppy is a continuous loop tape drive that was developed by Exatron for use with the Radio Shack TRS-80 microcomputer, among others, and was launched in 1979. The tape cartridge is about the size of a credit card, but about twice as thick...
".
QL Microdrive
Microdrives were also used as the native storage medium of the Sinclair QLSinclair QL
The Sinclair QL , was a personal computer launched by Sinclair Research in 1984, as the successor to the Sinclair ZX Spectrum...
, which incorporated two internal drives. These were very similar to the ZX Microdrive, but used a different logical format, allowing each cartridge to hold at least 100 kB. Mechanically the drives were similar however they ran slightly slower, and had a take-up acceleration start instead of the instant start of the ZX Spectrum drives - putting less strain on the cartridges themselves. The QL also included a Microdrive expansion bus allowing the attachment of up to six external QL Microdrives. These were never produced, probably due to lack of demand. It was however possible to connect ZX Microdrives to a QL by putting a twist in the cable.
In addition to the QL versions, dual internal Microdrives were included in the related ICL One Per Desk
One Per Desk
The One Per Desk, or OPD, was an innovative hybrid personal computer/telecommunications terminal based on the hardware of the Sinclair QL. The One Per Desk was built by International Computers Limited and launched in the UK in 1984...
system (also badged as the Merlin Tonto and Telecom Australia
Telecom Australia
Telecom Australia was the trading name of the:* Australian Telecommunications Commission * Australian Telecommunications Corporation * Australian and Overseas Telecommunications Corporation...
Computerphone). These drives were re-engineered by ICL for greater reliability, and used a format incompatible with both ZX and QL Microdrives.
External links
- ZX Microdrive information – At Planet Sinclair
- Sinclair User, April 1985, News section