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Top Forums UNIX for Dummies Questions & Answers Not quite related to Unix but CP/M file structure... Post 302149071 by porter on Tuesday 4th of December 2007 08:11:45 PM
Old 12-04-2007
The first byte is E5 if the file is deleted, this stems from the original formatting chips that filled blank disks with E5 (single-density) double-density were filled with F6.

When the entry is read into memory this first byte holds the disk number.

The whole thing is 32 bytes long and has room for 16 blocks to be recorded, if the file exceeds that length then another directory entry is added.

I'm a bit rusty but CPM groups sectors into allocation units, but a directory entry must still be able to say exactly how many 128 byte sectors it refers to.

Apparently those two reserved bytes are truely not used.

But I think you are missing a sector count.

0 db user type
1-8 db file name
9-11 db file type
12 db extent
13-14 db not used
15 db sector count
16-31 allocation map

So a disk can have a maximum of 256 allocation units, which may contain 2^N 128 byte sectors.

CPM is really designed for floppies, originally single sided, single density 8" disks.

Two pieces of information are not held on the disk.....

1. The starting sector, eg typically the operation system is held outside of the file format just in the sectors at the start of the disk.

2. The interleave map, as CPM is designed for 128 byte sectors and todays floppies use 512 byte sectors, a single real sector will contain multiple CPM sectors. Also, there is a translation from logical sector to real sector to allow the computer to process one sector while the disk is turning to the next one. Eg sectors may be ordered......

1 3 5 7 2 4 6 8


http://delivery.acm.org/10.1145/1000...FTOKEN=6184618
 

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DH_DI_NUMBERS(1)						     Debhelper							  DH_DI_NUMBERS(1)

NAME
dh_di_numbers - install numbered scripts into package build directories SYNOPSIS
dh_di_numbers [debhelper options] [dir [...] dest] DESCRIPTION
dh_di_numbers is a debhelper program that installs directories of numbered scripts into package build directories. Within each directory, there should be a "_numbers" file in which each line contains at least two space-separated fields. The first field in each line is a two-digit number, which will be prefixed to the entry name to provide ordering within the directory; the second is the entry name, which must correspond to a file or directory alongside the "_numbers" file; and the third field, if present, is another two- digit number which identifies another entry with the same entry name to which this entry should be a symlink. Any additional directory names specified as parameters will be installed in the package build directory of the first package dh_di_numbers is told to act on. By default, this is the first binary package in debian/control, but if you use -p, -i, or -a flags, it will be the first package specified by those flags. FILES
debian/package.di-numbers List the directories to install into each package and the directory they should be installed to. The format is a set of lines, where each line lists a directory or directories to install, and at the end of the line tells the directory they should be installed in. The name of the directories to install should be given relative to the current directory, while the installation directory is given relative to the package build directory. You may use wildcards in the names of the files to install (in v3 mode and above). OPTIONS
dir [...] dest Lists directories to install and where to install them to. The files will be installed into the first package dh_di_numbers acts on. SEE ALSO
debhelper(7) This program is a part of dh-di. AUTHOR
Colin Watson <cjwatson@debian.org> 3 2009-09-16 DH_DI_NUMBERS(1)
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