In Vol.23 No.1 l listed all the 3.5" 80-track versions of CP/M and PCP/M that are currently available to members of the SUC, as follows:-

At the time I published the above list I was familiar with all the MZ-80B and MZ-700 systems listed above and had used most of them in my work on Robin Hill's CONV.COM programs. But I had never booted either of the MZ-800 systems because I had never got round to fitting 3.5" drives to my MZ-800.

For the reasons explained below, that situation has now changed.

In April this year SUC member Terry Daly in Australia asked me for copies of the two MZ-800 systems listed above ( PCP/M80 and SDS/768 ). My first idea was to use the 3.5" PCP/M system on my MZ-700 to copy the 3.5" MZ-800 PCP/M system disk, and the 3.5" CP/M 2.2.2.12 system on my MZ-80B to copy the SDS/768 system disk - thinking that if this ploy worked, it would save me the chore of having to move a piggybacked pair of 3.5" disk drives from my MZ-700 to my MZ-800.

Unfortunately the ploy was only 50% successful; the MZ-800 PCP/M80 disk made on the MZ-700 was O.K., but the SDS/768 disk made on the MZ-80B was not. In the end, therefore, I was forced to move the 3.5" drives from my MZ-700 to my MZ-800, in order to make a copy of the SDS/768 system disk.

Once I had got over this hurdle and made the copy of the SDS/768 disk for Terry Daly, I could not resist the temptation to delve into the depths of both the 3.5" MZ-800 PCP/M systems, which I had never booted before.

As a result I can now give details of these two MZ-800 systems, and they appear on the following pages, in the 'General' section of this Magazine, because they form a natural supplement to the incomplete article on 3.5" CP/M and PCP/M systems that appeared in the General Section of the last issue.

In the process of investigating the two 3.5" MZ-800 systems and comparing them with the CP/M and PCP/M systems on other Sharp machines, I also carried out a thorough examination of the 'Disk Parameter Blocks' used by ALL the CP/M and PCP/M systems available on Sharp MZ-computers in the U.K.

The general concept of a 'Disk Parameter Block' is also dealt with in the 'General' section of this issue, but the full implications for each system on each machine are explained in the individual machine-centred sections.

This situation has now changed. A request for copies of the 3.5" PCP/M and SDS/768 master disks for the MZ-800 led me to discover that, although I could copy the PCP/M master under PCP/M on my MZ-700, I could not do the same for SDS/768 because it uses a completely different disk format.

I therefore had to find a way of moving a set of 3-5" disk drives from my MZ-700 to my MZ-800. After some thought, I realized that the easiest way was to simply pull out all the cables at the rear of my MZ-700 and connect my MZ-800 in its place - a very simple job which took less than 5 minutes.

I could then boot Robin Hill's 3.5" 80-track MZ-800 master disks of Sharp PCP/M and SDS/768 PCP/M, and this gave me the information detailed below.

These are virtually identical to their counterparts in Robins 3.5" MZ-700 PCP/M system, as listed on p.15 of the previous issue i.e.:-

FORMAT.COM displays the initial message 'Format 80 Tracks Vers 1'

COPYDISK.COM displays the heading 'MZ-800 P-CP/M80 - 80 Track Format'

DISKDEF.COM displays the heading:-

'DISKDEF MZ-800 PCP/M DISK DEFINE UTILITY VER 1.0A (C) SHARP Corp.'

The definition options are displayed differently but are essentially the same as in the MZ-700 version ( and once again, Drive A cannot be redefined, the prefix 'HD' means 80-track, and 'MZ800' may also be read as 'MZ700' ):-

( Drives C and D, if present, may be redefined in the same way as Drive B )

The opening screens of the SDS/768 utilities FORMAT.COM and COPYDISK.COM are more sophisticated than their Sharp counterparts, and give much more information. And the programs are very different internally, because the disk format used by SDS/768 differs from that used by Sharp's PCP/M.

DISKDEF.COM in SDS/768 appears very similar to its Sharp counterparts, but it is slightly more explicit and the options are in a different order.

SETUP.COM in SDS/768 offers 2 extra options relating to a RAMDISK facility.

The opening messages given by all these SDS/768 utilities are shown on the next page.

SDS/768 SETUP.COM offers the same 10 options as the Sharp version of the program. However, option 3 ( DEVICE ASSIGN ) contains two extra lines:-

By default, this program uses drive B:. In other words, if you type in the command 'FORMAT' on its own, the opening display announces that the program is ready to format a disk in Drive B:

To use a different drive add the drive designation on the command line. For example, to format a disk in Drive D: enter the command 'FORMAT D:'.

By default, this drive uses drives A: and B:. In other words, if you type in the command 'COPYDISK' on its own, the opening display announces that the program is ready to copy the disk in A: to the disk in B:.

To use other drives add the drive designations on the command line. For example, to copy from A: to D: enter the command 'COPYDISK A: D:'.

The opening display merely asks you to 'press any key to start'; but if you wish you may in fact exit back to the PCP/M system at this stage, without copying a disk, by pressing either CTRL/C or ESC.

The highlight in row A: is fixed i.e. it cannot be moved away from SDS/768. This reflects the fact that, like the Sharp version of MZ-800 PCP/M, the SDS/768 version of PCP/M may only be booted from drive A:, and the System expects that the disk in that drive will always be a system disk.

The highlight in row B: ( and in rows C: and D: if there are more than 2 drives fitted to the machine ) can be moved with the cursor keys in the usual way to redefine the relevant drive as required.

Note that in this version of DISKDEF the only disk definition that fits an 80-track 3.5" drive is SDS/768. All the other definitions fit a 40-track 5.25" drive ( SDS/400, 2DMZ800, 1D & 2DIBMPC, 2DMZ80B, 2DMZ3500, 2DMZ5500 ).

Therefore this version of DISKDEF is less flexible than the version that comes with Robin Hill's 3.5" 'Sharp' version of MZ-800 PCP/M, which offers TWO disk definitions that fit an 80-track 3.5" drive ( HDMZ800 and SDS/768 ).

In other words, Robin's 3.5" 'Sharp PCP/M' system can access a 3.5" SDS/768 disk; but his 3.5" SDS/768 system CANNOT access a 3.5" 'Sharp PCP/M' disk. This is a pity. and I intend to have a go at altering the SDS/768 version of DISKDEF.COM so that it CAN be used to access a 3.5" 'Sharp' PCP/M disk.

The two added lines in DEVICE ASSIGN ( Option 3 in SETUP.COM ) are related to the use of additional MZ-800 RAM as a 'RAM DISK'.

However, the only additional RAM pack that I know of for the MZ-800 is the MZ-1R18, which appears in all the standard MZ-800 brochures as an optional additional 64K 'RAM File'.

I therefore have no idea how you can add 256K, 512K or 1MB of additional RAM to the MZ-800, as implied by the added options in the SDS/768 version of SETUP.COM, and would be grateful for any information on this point.