Rough Guide to the Plus D
First appeared in ZXF issue 7 (Spring 2004)
SO WHAT'S A PLUS D THEN?
Released in 1988 by Miles Gordon Technology (MGT), the Plus D was a disk interface that allowed you to connect to your Spectrum pretty much any of the standard disk drives of the day. The interface was the successor by about two years to MGT's magnificent Disciple interface (a rival to the Sinclair Interface 1 which sat underneath the Spectrum - just like the IF1 - and also could connect to most standard disk drives as well as boasting ZX Net compatibility) and included also a 'magic' snapshot button and a parallel printer interface. It was compatible with most software designed for the Disciple and - due to the Disciple's own heritage - ZX microdrives. The original Plus D was black; the interface was later bought up by Datel and re-clad in a beige case.
WHAT'S SO SPECIAL ABOUT IT?
The Plus D was more than just another disk interface. The functionailty of a Spectrum 128/+2 fitted with a Plus D system (interface and disk drive) far exceeded the functionality offered by the other main upgrade route for Spectrum owners at the time - the Spectrum +3. And upgrading to a Plus D was cheaper. At the start of 1989, for example, a +3 with a Multiface 3 (a peripheral for the +3 by Romantic Robot with its own 'magic button' for creating snapshots files - the +3 itself came with nothing like this) would have cost you £245; a Plus D system was faster, larger (up to 780k), had a much more sophisticated OS, was more compatible with existing Spectrum software than the +3 was, and cost just £140. The sheer power of a Plus D system, therefore, made it extremely popular with those who owned it. Although it was never supported by commercially released games, a very loyal user-base evolved; the system was supported by the long running Format Magazine (pictured left) of the INDUG user group.
HOW DO YOU GET IT TO WORK?
The Plus D uses a very straightfoward syntax; the main thing to remember is that LOAD and SAVE commands are suffixed by either D1 or D2 depending on which drive you are accessing (the Plus D can support two). Thus:
LOAD D1 "zxf"
LOAD D2 "zxf" CODE
MERGE D1 "zxf"
SAVE D1 "zxf"
SAVE D1 "zxf" LINE 10
SAVE D2 "zxf" SCREEN$
Although the interface pretty much refuses to work in physical conjunction with a Sinclair Interface 1, you can use the IF1's microdrive syntax in preference to the syntax above, so programs modified to work on a microdrive should work also on a Plus D formatted disk. Thus:
LOAD D1 "zxf" could alternatively be typed as:
LOAD *"m";1;"zxf"
SAVE D2 "zxf" LINE 10 could alternatively be typed as:
SAVE *"m";2;"zxf" LINE 10
Other self-explanatory commands:
CAT 1
ERASE D1 "ZXF"
VERIFY D2 "ZXF"
Snapshot files were denoted by an 'S' suffix for a 48K snapshot and a 'K' for a 128K snapshot, ie:
LOAD D1 "zxf" S
or
LOAD D1 "zxf" K
Want to know more? You'll be delighted to learn, then, that the original Plus D manual can be downloaded from the documentation page at WoS (www.worldofspectrum.org/documentation.html). RealSpectrum authors Ramsoft have written a document of their own (the DOS version of RealSpectrum supports the Plus D), which can be found at www.ramsoft.bbk.org/tech/mgt_tech.txt
SO HOW DO I GET HOLD OF ONE?
Original Plus D interfaces can fetch a fair old price on ebay - especially if they come with a disk drive included - prices can often exceed £50. Also, they don't come around very often.
Alternatively you could try building your own Plus D clone. Designed by Philip Mulrane, you can download the schematics for this from the 'I can´t believe it´s not the +D!' pages at www.worldofspectrum.org/NotThePlusD/. Philip's own clone is pictured above on the right.
Sintech (www.sintech-shop.de) have been making and selling these clones for a while now, so you don't have to be an electronics whiz to be able to get your hands on one. The Sintech clones come uncased, however. So you might have to try your hand at a bit of metalwork (the Plus D's metal case doubles as a heat sink) if you're one to blush at the sight of it naked.
Another thing to bear in mind is that Plus Ds generally don't like modern floppy disk drives. You have to remember that at the time of its original creation high density drives weren't around yet - and today it's not possible to walk into a high street shop and buy anything other than a high density drive. Also, modern floppy drives are designed with the PC in mind. Happily, Sintech can also supply you with a compatible drive for around £17.
SO HOW DO I EMULATE ONE?
If you can't wait for the next version of Spectaculator (or can't afford it), RealSpectrum from Ramsoft (www.ramsoft.bbk.org) has supported the Plus D for some time now. The support this emulator gives is mightily impressive actually - not only can you work with Plus D disk images on your hard disk (these go by the extension .IMG), but you can actually access real Plus D formatted disks from your PC's floppy drive. Alas, this feature is not available in RS32 - the Windows port of RealSpectrum - and the DOS version in which it is available tends not to work on Windows XP systems. You can still work with Plus D disk images in RS32, however.
What's more, search for "Plus D" on Sinclair Infoseek at WoS and, right at the bottom of the page, you'll see a file called 'plusdtools.exe'. Download and run this and it will extract to a number of small DOS programs which appear to run quite happily on Windows XP, using your PC floppy drive to work with real Plus D formatted disks. They include:
SCAT.COM - CAT A: or B: of diskette ( Type "SCAT /?" )
SPIM.COM - Copies diskette image to Harddisk ( Type "SPIM /?" )
WHERE CAN I GET SOFTWARE FOR IT?
One of the best sources of Plus D software is from the Alchemist Research PD Library, archived at ftp://ftp.worldofspectrum.org/pub/sinclair/alchemist-software/. The library is stored as a series of disk images using the Teledisk format, so you'll need to unzip the files first and them convert each of these using Teledisk (a very old DOS program, a copy of which is linked to from www.worldofspectrum.org/trdos.html) onto an old double sided, double density disk (note - this appears not to work on a Windows XP machine). Before your very eyes your old floppy disk will transform into a Plus D formatted disk containing all the files, which you can them load straight into a Plus D system, an emulator with real disk support or alternatively convert it into a .IMG image file using, for example, RealSpectrum's built-in disk image creator (again, this won't work on an XP machine, since RS32 doesn't support real disk access - you'll need to use the DOS version of RealSpectrum running on an older OS). It's quite a lengthy job and arduous job, and there are a lot of files to convert - discs full of demos, games and utilities; hopefully some very kind soul will one day go through all of this and upload the resulting .IMG files to WoS (although it might well be best to hang on and see if the Plus D enabled version of Spectaculator continues with the .IMG format or creates one of its own before comitting any time to doing this).
