>>> from http://www.shadowmagic.org.uk/cssfaq/reference/diskreference.htm The Opus Discovery provides several different expansions in a single unit, featuring a Joystick port, pass-through expansion connector, parallel printer port, a composite video/monitor output and a single 3.5in disk drive that supports disks of up to 250K in capacity (178K when formatted).
An upgraded model, the Discovery 2, was also introduced that featured 2 drives. The Discovery 1 could be upgraded to the Discovery 2 by returning the system to the manufacturer. The power supply for the Opus replaces the original Sinclair model, and is used to power both the interface and the computer.
Operationally quite similar to the Microdrive (albeit with disks), the same commands are supported by both the Discovery and ZX Interface I - this reduces the 'learning-curve' quite dramatically and allows many programs with ZX Interface I & Microdrive support to be easily adapted or use without difficulty. The ZX Microdrive is faster, however.
Documentation: The Complete Opus Discovery Shadow ROM v2.2 Disassembly. Opus Discovery Block Diagram.
The Discovery 1 cost £199.95 when originally introduced and the Discovery 2 cost £329.95. The upgrade from Discovery 1 to Discovery 2 (known as the Discovery Plus) cost £139.95. Emulation of the Opus Discovery is provided by RealSpec for MS-DOS and Microsoft Windows systems.