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Interface 1

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Best search term:  (zx,sinclair) interface (1,one,i)
Availability:  Fairly common
Typical value:  £30-£40
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Interface 1 was perhaps the most interesting of Sinclair Research's small peripherals range. As well as providing connectivity to the Microdrive mass storage device, Interface 1 also serves as an RS232 interface and local area network (LAN) device. The device fits underneath the Spectrum, tilting the keyboard to a more comfortable typing angle. Unlike the RAM packs, it has no "wobble" problem, as it can be secured in place with screws passing through the device into two existing screw holes on the underside of the Spectrum.

Most users of the interface would have used it to connect to the Microdrive - it was sold in a special "ZX Spectrum Expansion System" package along with the Microdrive for £79.95, or £49.95 on its own. Connected to the Interface via ribbon cables, up to eight Microdrives can be connected at once.

The RS232 (serial) interface was a fairly standard design, capable of being used at up to 19.2Kbps with devices such as printers and modems.

The network interface was perhaps the most interesting element. A LAN (or "ZX Net") is set up by simply joining two Spectrum interfaces together with the 10-foot long net lead. Up to 64 Spectrums connected at 100 baud can be connected this way. A broadcast feature enables one Spectrum to transfer data to any other machines connected to the network, and that one machine can also be used as a server - for example, to provide printer output from any other networked machine.

The network facility was in fact the original raison d'être of the Interface 1 - the Microdrive interface came at a later stage - and was probably intended to improve the Spectrum's usefulness in an educational environment. A class issued with networked Spectrums, for example, could be supervised by a teacher with a master terminal. If this was the intention, then it seems to have fallen somewhat flat - Sinclair captured only a paltry share (less than 2%) of an educational market overwhelmingly dominated by Acorn's BBC Micro.

The Interface 2 (in its original form as a network interface) was planned even before the release of the ZX Spectrum in April 1982. The Spectrum came with a number of initially mysterious commands on the top row of the keyboard - OPEN #, CLOSE #, MOVE, ERASE, CAT and FORMAT. On a Spectrum 16K or 48K without an Interface 1 plugged in, these commands do nothing much. In fact, they are not even present in the ROM; the machine has to call a "shadow ROM" hosted in the Interface 1 to handle these commands. This was due to slippage in Sinclair's development of the Spectrum and its peripherals. After the premature departure of the Spectrum's designer, Richard Altwasser, in February 1982, the development schedule was thrown way off target. The Spectrum consequently shipped with what amounted to an unfinished ROM, with 1300 bytes unused - a comparatively huge amount at a time when every last byte counted. This gap was where the networking code would have resided, hence the computer's reliance on an external "shadow ROM" which switched in and out as needed.

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Chris Owen 1994-2003