From: joe@user.com   
      
   "Kelly Leavitt"  wrote in message   
   news:1149274766.551836.59180@y43g2000cwc.googlegroups.com...   
   > vad wrote:   
   > > Stumbled across Vernon Hester's analysis of the major TRS-80 DOSes.   
   > > This excerpt comes from the MultiDOS manual, Cosmopolitan Electronics   
   > > Corporation, 1984, and shows a good  summary of different formats   
   > > TRS-80 disks employed.   
   > >   
   > Some great information. I'm in the process of writing a program to   
   > manipulate disk images of the model II/12/16/6000 lines. Does anyone   
   > know of something similar for those computers?   
   >   
   > My goal is to be able to extract files directly from the images under   
   > windows, and eventually to be able to write to these files too.   
   >   
   > Kelly   
   >   
      
   Up through TRSDOS 2.x there was a program that made the rounds for the   
   Model II machines called SuperZap.  (There was also a similar version for   
   the Model 1/3 machines)  Anyway, through 2.x it was every easy to display   
   the disk.  There was a 'read sector interrupt' and a 'write sector   
   interrupt'   
   Just load up registers and do the int function and that was that.   
      
   2.x was simple.  26 sectors per track, in groups of 5 x 5 with the 26th   
   sector   
   an 'id' sector.   Or in the case of the Model II diags, a backup protection   
   sector.  There was a marker on one track in sector 26 that was looked for   
   and if found, the disk would NOT run.  It essentially forced you to make a   
   backup and run that.  (Way too many techs were crashing their diag disk   
   and then shops would have to order more from National Parts (with a fee   
   of course!) and the directors were getting POed.)  If you duplicated the   
   master disk with FastBack, then it copied the special sector, but if you   
   used the TRSDOS to backup the diskette, then the sector wouldn't be   
   copied.   
      
   In 2.x, the disk was 'divided' into first half and second half, counting in   
   from   
   the boot track which was the outermost track.  If I remember correctly the   
   interleave was 5.  Well, not exactly, it was designed so that each 'cluster'   
   of   
   5 was read on one revolution, with 26 the id and out of the interleave.   
      
   The 'backup protection' on the diag disk wasn't to prevent you from making   
   backups, it was to FORCE you to make a backup before you could use the   
   diskette (and risk ruining it).   
      
   With 4.x the interrupts disappeared.  In addition, the format changed from   
   sectors of 256 bytes to 512 bytes, and the interleave changed a few times   
   based on the version.  There were ways to call the sector read/write   
   routines in 4.x, but you had to find the entry point first.  It was almost   
   as   
   if someone got the clevers and didn't want certain utilities to be run...   
      
   Mike   
      
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