+D
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The +D (or Plus D) was a floppy disk and printer interface for the Sinclair ZX Spectrum home computer, developed as a successor to Miles Gordon Technology's earlier product, the DISCiPLE. It was designed to be smaller, cheaper, simpler and thus more reliable.
It discarded a number of the less important features of the earlier product — the network and joystick ports, the inhibit button and the pass-through connector — and replaced its ancestor's plastic wedge-shaped design which fit under the Spectrum with a simple flat metal slab which protruded from the rear of the computer.
It provided only floppy-diskette and Centronics parallel interfaces, plus a Non-Maskable interrupt button. The +D's casing was simple folded steel, which was not only stronger than before but acted as a heatsink, improving reliability. Apart from the missing ports, though, it was software-compatible with the larger device.
The +D's DOS was named G+DOS, and was compatible with the DISCiPLE's DOS, GDOS. SAM DOS for MGT's SAM Coupé was backwards-compatible with GDOS and G+DOS.
The +D and DISCiPLE so extended the capabilities of the Spectrum that a user group was formed to discuss the system's newly-expanded potential. The group, INDUG, published a newsletter called Format, and later went on to become Format Publications.
For more information on the design, specification and use of the +D, see the entry on MGT.
The +D design was later licensed by Datel and it continued on sale for some years after MGT's demise.
