CP/M archive to image 8" CP/M floppies
dave04a at dunfield.com
Mon Sep 19 08:26:26 CDT 2005
>> While images are nice, for CP/M there is another alternative that may be
>> more widely useful and easier, although it's less historically accurate.
>> That is just to copy the files over to MS-DOS disks, where they can then
>> exist in folders on a modern hard drive or be put on CDs or DVDs. I can
>> really see no advantage to a strict "image", as long as one has the files.
>> The issue that this leaves out is the system tracks, but that is easily
>> dealt with: Runs "SYSGEN", exit, and then do a "SAVE 34 SYSTEM.COM" and you
>> have the system tracks as a disk file in a format that is easily restored
>> simply using SYSGEN.
>> This method also has some actual advantages, in terms of being able to
>> actually use the software with a CP/M emulator on a PC.
>> Since I'm not aware of any CP/M programs that did copy protection or any
>> other type of manipulation that would require an exact disk image, I don't
>> really see the drawback of this approach.
>The one main drawback is that this is not an accurate or appropriate way
>to create an image for historical preservation. For this reason I
>recommened against what you describe.
Somehow I missed the beginning of this thread (had a few mail probs lately),
so please forgive if I am wandering too far away from the original topic, but
I gather we are trying to figure out how to best preserve CP/M disks.
I to agree that copying the files is not the best solution - even if you do the
SYSTEM.COM thing, you still need a working CP/M boot disk to be able to make a
boot disk (chicken and egg type of deal) - Having restored a number of systems
for which I did NOT have an original boot disk, I can tell you that this can be
I've used ImageDisk to backup and restore quite a few CP/M disks by now, and it
works well, deals with system tracks just fine, and allows you to make a bootable
disk from "starting point zero". It does have two limitations:
- For 8" systems, you will have to attach an 8" drive to your PC ... I've put
up a page on my web site which describes this in a bit of detail, including
an adapter thats very easy to make to convert the 8" interface to plug into
a standard 5.25" cable.
- The disk format must be one that is compatible with the PC's 765 controller
The only work-around for this is to use CPT.
For cases where the disk format is not compatible with the PC (hard or non-IBM
format sectors), I have created CPT (CP/m Transfer) which is also available on
my site - CPT transfers disk images to and from the actual target system over the
serial port, and can work with ANY format disk (because it uses the targets disks
and controller). CPT has a different set of limitations:
- The target system must have a serial port (it doesn't have to be the console).
- You need to provide a very small binary serial port driver for the CPT resident
client. Even if you don't know how to talk to it, looking at the device number
of the UART, and a few minutes tracing vectors and disassembling with DDT will
usually give you the info you need.
- CPT can't always handle system tracks - CP/M does not provide a standard way to
read/write the system tracks, and on some systems they are different from the
user tracks and incompatible with the system floppy driver. CPT allows you to
skip them, and you could use SYSGEN/SAVE to place a copy of them in the user
- CPT requires you to have a working target system backup and recreate the disks.
It *SHOULD* be possible to save a memory image of loaded CP/M and FORMAT which
can be loaded into a bare system to create a formatted disk. I have not had to
do this with CP/M yet, but I have done it with Cromemco RDOS which is similar.
Note that you still need a means of getting the memory image into memory and
launching it at the right address (for Cromemco you can use RDOS) - I have a
very tiny (<500 bytes) 8080 monitor which would work for this purpose.
With CP/M you would need to have a second memory image with SYSGEN, and system
tracks preloaded in memory, and possibly a third with the CPT client preloaded
- but these should be possible, at which point you could use CPT to transfer
over full disk images.
I've been toying with the idea of writing a program to allow you to list the
directory, and import/export files to/from a CP/M ImageDisk image (or perhaps
just a straight binary disk image which IMDU can create)... This would allow
the files to be used under a CP/M simulator that uses the DOS file system
fairly easily ... too busy to even start right now, but perhaps sometime this
dave04a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Collector of vintage computing equipment:
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