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Advice on additional disk drives for the Spectrum +3            J. Elliott, 1993
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  The Spectrum +3 comes supplied with one disk drive, built-in. This file
contains information and advice about fitting a second ("B:") drive.
  There are two main options:
  1) The Amstrad recommended 3" drive, referred to in chapter 10 of the manual.
  2) A third party 3.5" drive.

rThe Amstrad FD-1:u

  This is almost identical to the built-in ("A:") drive. It will interchange
disks quite freely, but you can still only get 173k per side of a disk (192k
with special format programs). It is quite rare nowadays, since 3" drives are
obsolete. It will work happily with CP/M DISCKIT.

rA third-party drive:u

  There are three main models:

1) CPC type external B:. An example is the GVL external CPC6128 B: drive.
   This particular drive can be used as a 2x192k drive, like the FD-1, or as a
   784k double-density drive. The changeover is made by moving a switch on the
   back.

2) DATADUAL-8 by Pinboard Computers. This has a switch on the front which
   changes it between a 784k B: drive, a 2x192k A: drive and a 784k A: drive.
   It can be used to replace a failed A: drive. Note that it cannot be used as
   a 2x192k B: drive. See "Notes on 784k A: drives" below.

3) DATATWIN-8 by Pinboard. The top-of the range model, it has two drives. One is
   a replacement A: drive and the other is a B: drive. Switches on the rear
   allow you to choose between the drive in the +3 or the drives in the
   DATATWIN. The top drive can be a 2x192k A: drive or a 784k A: drive. The
   bottom drive is a 784k B: drive. See "Notes on 784k A: drives" below.

rFormats:u

  Disks made by the +3DOS "FORMAT" command have 173k per side. 3.5" disks cannot
be turned over but 2x192k drives have an extra switch to tell the drive which
side of the disk to use.
  All 3.5" disks can hold up to 784k (this uses both sides of the disk at once),
and +3DOS can use these formats. The problem is that it can't make them. Disk
drives tend to come with utility disks allowing you to format disks to 720k or
more, but these formatters will be for PCWs or CPCs. Unless you own a PCW or
a CPC, the formatters will be useless. If you bought a CPC accessory, you will
be confronted with a lot of text about "RamDos, RomDos, MS800" etc. pIGNORE ITq.
The fact of the matter is that while CPCs can't really handle formats bigger
than 192k without extra software, Spectrum +3s can. The only thing they can't do
is format the discs.
  There is therefore on this disk a program: DU50. It is the same as the CP/M
disk formatter DU49A.COM, but rewritten for the +3. It allows you to format
disks to up to 784k, which +3DOS will recognise automatically afterwards. It
can also format 3" disks up to 192k. DU50 is written in machine code, which is
stored in the file: DU50.HED. It is essential to format with DU50 if the drive
you are using is a "720k-only" version.

  You should turn the disc drive and the TV on before turning on the +3.
Unfortunately this makes the disc drive rattle and emit peculiar noises; the
solution I reached was to disconnect the TV aerial lead before turning on and
only reconnecting when everything had warmed up.

rSoftware:u

  If you get a CPC6128 B: drive, the documentation will tell you that special
software is needed to use the drive with 784k disks. This is not true for the +3
which can recognise 784k disks automatically both in +3DOS and CP/M.

  The Pinboard drives have a "720k booting" option, allowing PCWs to boot from
720k 3.5" disks. This software should pNOTq be used on the +3. Instead,
you should use P3MAKE (in this archive) which writes +3 boot sectors onto
720k discs.
  Recent Pinboard drives also come with 'FIB' files which allow PCWs to use the
3.5" drives at higher efficiency. These should not be used with the +3.

  Most programs should be able to recognise drive B:. An exception is Multiface
3, which always uses drive A:. Even if you copy M3 saved programs onto B:, the
program (eg "GAME") will always try to load its code (eg "GAMEC") from A:. Some
programs (eg PAW) should be set to use B: as a data drive (with PAW this is
done with the Y menu). Others should just have B: put in front of the filename.

rThe ABBA Switchu

This is a little device which plugs into the back of the +3 and swaps the disc
drives over (so that the built-in drive becomes drive B: and the external drive
becomes drive A:). Again, it is designed for CPCs, so please note the following:

1. The second paragraph of the fitting instructions needs to be modified, since
  the +3 has a red lamp on top. Open the computer a little and you will see two
  wires running between top and bottom. At the bottom end they are connected to
  the circuit board by a small plug which should be disconnected. Remember to
  reconnect it when you reassemble.

2. When you are using the 3.5" drive as drive A:, the built-in disc drive will
  have its light permanently on. This is nothing to worry about.

rNotes on 784k drive A:u

  +3DOS will work perfectly whether Drive A: is 784k or 192k. However, format
programs (including the FORMAT command) find difficulty in re-formatting 3.5"
discs from 784k to 173k. This will probably only apply for ABBA switch users.
The program I use to perform this is Supersoft's "Disc Doctor", which has one
very useful option to format 173k discs quickly without trying to read from the
disc (which is what causes the problems).

  +3 CP/M will normally only boot from a 173k disc formatted with DISCKIT. The
best way to do this is to format a new disc in the 3.5" A: drive under +3DOS
and then use the command COPY "B:" TO "A:" with the CP/M master disc in the 3"
drive and the new disc in the 3.5" drive. Once you have used a 720k or 784k
disc in the 3.5" drive, you can't use any 192k or 173k discs in it until you
reset the computer. It is possible to have +3 CP/M boot from a 720k disc -
see P3MAKE.DOC.

rOrdering:u

  When ordering, always state that you have a Spectrum +3, and send a photo-
copy of pages 314-5 of the manual (describing the disk socket). Spectrum +3
drives MUST have an additional power supply.

rSPEEDUPu

If you are lucky enough to have twin 3" drives, or if you are confident that
you will not need to use the 3" drive until you next reset the computer, then
you can run the program SPEEDUP on this disc. It sets both drives to the timing
parameters for 3" drives, so you pmust notq use the 3" drive after running
SPEEDUP, until you reset the computer or run SLOWDOWN (the opposite program).
The CP/M equivalents SPEEDUP.COM and SLOWDOWN.COM are also suplied.
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