The ZX Microdrive is a magnetic tape device for mass storage of data, which was brought by the company Sinclair Research in July 1983 for the ZX Spectrum home computer on the market and was touted as a cheaper alternative to floppy drives. The Microdrive stores the data on individual replaceable plug-in modules (approximately 5 cm × 3.5 cm × 0.5 cm). In the module there is a connected to an infinite loop Chromdioxidband, half as wide as that in the popular at that time audio compact cassettes. A complete run of the tape takes 7.5 seconds. Each plug-in module had an internal memory of 100 KB, with a transfer rate of 16 KB per second. Due to the running noise and the unusual construction method, this band was like back then titled in the jargon as " breakneck laces ". The " stringy floppy" for the TRS -80 worked on a similar principle.
The drive only mechanically ( for tape guide ) modified stereo sound head is used for reading and writing the bits. The miniaturization of mechanical parts leads to rapid wear and the special cassette is fast unreliable and eventually unusable. The individual plug-in modules were relatively expensive. Technically requires the ZX Microdrive as a controller called the ZX Interface 1 for connection to the ZX Spectrum. This extension, which also provides serial interfaces and a rudimentary network functionality, was usually sold with the real Microdrive.
The Microdrive technology was later used for the Sinclair QL computer. The main developer of the Microdrive was Ben Cheese. The Microdrive itself following development were subjected to:
- The ZX Spectrum and the then customary in home computers cartridge drives supported in the usual tape drives sequential storage. However, the QL that it stores exactly the familiar with disk drives division into sectors with net 512 bytes, a dynamic and flexible directory and the DOS cluster table similar so-called Sectormap ( Microdrive format used 1 sector per cluster, the so otherwise identical format to the QL -floppies with 720 KB used three sectors per cluster).
- When formatting bad sectors were detected in the QL and automatically drawn through entry in the Sektormap from circulation.
- The storage of the QL is superior to MS -DOS format. The root directory has no fix, but a flexible length.
- The data in the Sectormap are optimized for the special tricks of the QL operating system: unlike MSDOS computers with a larger read request is everyone on the read head just passing by cluster belonging to this order, read in any order immediately and QL- memory appropriately inserted. Thus, a fragmented file to be completely read by the Microdrive in no more than a single volume through the loop ( about 7.5 seconds). Defragmentation does not support Spectrum and QL against it.