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Kaypro doesn't store ALL of its CP/M in the reserved track

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    Kaypro doesn't store ALL of its CP/M in the reserved track

    I was analyzing all the downloadable disks on the web that I could find for my Kaypro 4/83 and I found something interesting. First the one says "KAYPRO II 64k CP/M vers 2.2" and the other says "KAYPRO IV 64k CP/M vers 2.2". They are virtually identical other than that difference and about 20 bytes at the end which could be configuration maybe.

    The first track is reserved (10 sectors * 512 = 5120 bytes). Then if on a flat image, another 2048 bytes beginning at 0x1c00 is a continuation of CP/M. It is actually block 1 in the file system and is the 2K following the directory (64 entries * 32 bytes). I then noticed on some disks with files that they begin at "2" and not "1". Would they possibly have patched CP/M not to use block 1 as to keep this area from being overwritten? How does this work with tools like cpmtools? The kpiv diskdef seems unaware of this unless I'm not getting it.

    Yes, I got a "fix" for this in the latest cpmtools. Basically, Kaypro reserved two full blocks for the directory, but only used the first 64 entries. The diskdef for the latest cpmtools version is:
        seclen 512
        tracks 80
        sectrk 10
        blocksize 2048
        maxdir 64
        dirblks 2
        skew 0
        boottrk 1
        os 2.2
    Note the new parameter "dirblks" that tells cpmtools to reserve two blocks even though only 64 entries are used.

    In the CP/M DPB this is accomplished by having DPB.DRM=63 and DPB.ALV0=11000000B

    and, yes, this all came after trashing several formerly-bootable Kaypro disk images by using cpmtools on them.
    - Doug


      Where can I download/find that latest cpmtools?


        I had thought these got merged, but alas no action from Michael Moria, official owner of cpmtools, or on pull request at You can take cpmtools-2.21 from github and either add the commit from my pull request or apply this patch (attached).

        This commit/patch also fixes the Kaypro diskdefs, but does not change any other possible formats that might suffer from this (the only ones I know of are Kaypro).

        If you're not fluent in git/github, let me know and I can make a tarball of the source for that commit. I only have Ubuntu 20.04 Linux on x86_64, so if you need binaries for a different platform we'll have to work something out.
        Attached Files
        - Doug


          I could use win32 binaries, but I don't want you to have to go through a lot of work. Will Michael eventually get it integrated?


            I don't have any way to produce Windows binaries. I will push on the (which is not Michael) pull request to get the integrated, but I don't believe that that repo is used to distribute binaries so someone with a Windows C development kit would need to do that (maybe cygwin is all that's needed?)
            - Doug


              No worries - in the meantime I suppose I can just expand maxdir to take up the area, but never copy more than 64 files to it!


                Originally posted by alank2 View Post
                No worries - in the meantime I suppose I can just expand maxdir to take up the area, but never copy more than 64 files to it!
                Yes, in theory. But you have to watch out for files that overflow the first directory entry, as each entry consumed by a file works toward that "64".
                - Doug


                  Ahh yes, that is right.


                    Still thinking about how to "workaround" this issue without having to recompile cpmtools. My other thought was to just create a directory entry that holds that block used. It could even be named CPM22.BIN or something.


                      Originally posted by alank2 View Post
                      Still thinking about how to "workaround" this issue without having to recompile cpmtools. My other thought was to just create a directory entry that holds that block used. It could even be named CPM22.BIN or something.
                      Yes, that's what I did for awhile with my simulator disk images before fixing cpmtools. It works best when creating new blank images, for existing images with files it is a bit trickier. But if you are manually "editing" the directory you can just create the entry and list the block(s) in the appropriate part of the entry. Keep in mind that DS disks use 2K block size and thus the reserved block is 01. For the SS disks (1K block size) it is blocks 02 03. Might just be easier to tell cpmtools that you are using 128 directory entries and just be cautious not to overflow 64.
                      - Doug


                        I made a quick disk tool to convert disks or extract/import cp/m on them, so maybe I'll just add a "protectfile" option for it that adds a file that protects it. For DSDD it would only have to have one allocation block 01, but for SSDD it sounds like it would need two, for 02 and 03. I think 00/01 are still taken up by the directory. I suppose I could even put the protectfile in user 15 where no one is likely to find it.


                          Thanks for this patch. As a Kaypro owner, I had occasionally trashed a Kaypro cpm disk image but never investigated further.


                            Doug - I emailed Michael and he said that he got some changes from you. He gave this link:



                              Originally posted by alank2 View Post
                              Doug - I emailed Michael and he said that he got some changes from you. He gave this link:

                              Yes, looks like all of my current patches are included in the latest snapshot, except an enhancement that we are still discussing (a way to embed the entire (single) deskdef in the -f parameter).
                              - Doug