comp.sys.sinclair FAQ

The original ZX Spectrum was introduced before floppy disk drives were a realistically affordable option for most home users. Within a few years, however, prices had fallen to such an extent that a large number of disk interfaces and drives were available that could be readily, and inexpensively, purchased by the 'average' user.

In the intervening period, a number of alternative systems were developed, including the Rotronics Wafadrive and ZX Microdrive. These systems are 'hybrid' designs, being based on endless-loop cassettes. These systems proved very popular, and offered high capacity storage with much greater reliability and speed than normal cassettes, without costing substantially more in media terms.

The drives listed below represent a small number of those available.

• ZX Spectrum +3 Disk Drive
  The disk drive on the +3 is controlled by three ports:
  
  
  • 0x1ffd: Setting bit 3 high will turn the drive motor (or motors, if you have more than one drive attached) on. Setting bit 3 low will turn them off again. (0x1ffd is also used for memory control).
  • 0x2ffd: Reading from this port will return the main status register of the uPD765A (the FDC used in the +3).
  • 0x3ffd: Bytes written to this port are sent to the FDC, whilst reading from this port will read bytes from the FDC.
    
    
  For more information on the uPD765A, see the CPC Guide section at the Unofficial Amstrad WWW Resource, as the Amstrad CPCs used the same FDC; the documents most relevant to the +3 are the first two in the 'Disks' section.
  
  In addition, it is possible to add an Amiga 3.5" drive to a Spectrum +3 by simply wiring the pins by name and providing it with an external power source (which can be an Amiga PSU with increased amperage, used to power the entire +3 and external drive) There is a public domain formatter around to format it to 720k - this is quite useful as 3" disks are now a rarity and were never that reliable.
  
  
• Timex Disk Drives
  There are two versions of the disk system created by Timex Portugal, the FDD and the FDD-3000. Both require a machine specific interface. These were sold for the TS2068, TC2068 and TC2048 machines but third parties have subsequently supplied interfaces which work with the 128K ZX Spectrum (these are also required for the TC2128 and TC2144).
  
  Both systems have their own Z80 CPU but while the FDD only has 16K of RAM, the FDD 3000 has 64K and can be used as a CP/M terminal. The FDD consists of three separate boxes while the FDD-3000 integrates a PSU and two 3" drives. It is possible, although tricky, to upgrade an FDD to an FDD-3000. Both systems can use 3.5" and 5.25" drives in place of (or in addition to) the 3" drives.
  
  The interface uses a logic circuit to page in the 4KB FDD ROM whenever there is a call to 0x0000 or 0x0008 and page it out again whenever there is a call to 0x0604. When it is needed the FDD ROM is paged in at 0x0000 and 0x1000 and the area 0x2000-0x3fff holds eight copies of 1K of RAM or four copies of 2K of RAM. The disk drive is controlled by port 0xef.
  
  
• Opus Discovery
  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.
  
  
• Crescent Quick Disk
  Three different versions of the Crescent Quick Disk were introduced; the 128, 128i and 256i. The 128 was intended as an add-on drive for existing systems and was not supplied with a disk interface. The 128i includes the required interface, with the 256i being a high-capacity version of the 128i. Storage capacities are as the names imply, and each system included an RGB socket and RS-423 interface, and are compatible with either the ZX Spectrum or ZX Spectrum +.
  
  The Crescent 128 cost £99.95 when introduced, with the 128i and 256i costing £129.95 and £229.90 respectively.
  
  
• MGT Lifetime Disc Drive
  Please refer to the MGT Lifetime FAQ, developed by Damien Guard, for full technical details of this device.
  
  
  • Documentation:
    
    • MGT Lifetime User Manual.
  
  The FAQ is very comprehensive, with sections detailing how to configure this drive for use with many different types of system.
  
  
• Triton Quick Disk
  The Triton Quick Disk system, produced by Radofin Electronics (who also distributed the Mattel Aquarius), allowed up to 100K of data to be saved on double-sided 2.8" disks (50K each side). Data is recorded in a 'spiral' pattern, rather than in concentric circles. Compatible with the original ZX Spectrum and ZX Spectrum + systems (and others).
  
  Up to 2 drives can be connected together (multiple interfaces are required), and the drive features a pass-through connector that allows a ZX Printer to be connected if desired.
  
  
  • Data transmission rate: 101.6K Bits per second.
  • Density: 4410 BPI.
  • Disk type: 2.8" double-sided.
  • Disk capacity: Up to 100K, 20 sectors per side, 2.5k per sector.
  
  Although marketed as a floppy-disk drive, the Triton Quick Disk can more accurately categorised as a 'stringly-floppy'-style system, like the ZX Microdrive and Rotronics Wafadrives, since 'disk' access is sequential rather than random. The maximum seek-time is approximately 8 seconds. The Triton Quick Disk originally cost £119.95.
  
  
• Omnitronix Pacer
  The Omnitronix Pacer system comprises several different parts, each of which could be purchased separately for use with compatible products. The disk interface connects to either a ZX Spectrum or ZX Spectrum + via a short ribbon cable attached to the edge connector, and supports 5.25", 3.5" and 3" disk drives.
  
  A complete system could be purchased that included the interface and a 5.25" disk drive, offereing up to 100K of storage on single-sided, 40 track disks. An enhanced system that included the interface and a 400K capacity 5.25" double-sided 40/80 track disk drive was also available.
  
  The disk interface cost £79.95, with the complete systems costing £119.95 and £189.95 respectively.