╔════════════════════════════════════╗
                   ║    COLUMBUS - The Disk Explorer    ║
                   ╠════════════════════════════════════╣
                   ║ (C) Copyright 1987 AWARE SOFTWARE  ║
                   ║      Programmer - Mark Cummins     ║
                   ╚════════════════════════════════════╝

   COLUMBUS was written to complement the PATCH program by John Smith which
appeared on the August PC PLUS disk. PATCH allows you to edit any file in
blocks of 128 bytes. Now COLUMBUS allows you to get down to the nitty gritty
of editing a disk at the track and sector level.

   COLUMBUS is useful for doing "dirty" work like hiding subdirectories and
files, recovering files, and just having a look at how MSDOS stores its files.
The command set used by COLUMBUS is very similar to PATCH's so you should have
no problems moving between the two programs.

   Please note that COLUMBUS will only work on floppy disks. Always work on a
backup as the wrong byte in the wrong place could destroy the data on the
entire disk.

   To run COLUMBUS type the following at the A> prompt:-

A>COLUMBUS [d]    d = disk drive to edit (A: or B:) and press <RETURN>

   Table 1 below shows where the MSDOS control areas are located on MSDOS
version 1,2, and 3 disks.

Table 1. Locations of Boot Record, File Allocation Table, and File Directory
==============================================================================
                            MSDOS 1                     MSDOS 2&3
                 Single-sided   Double-sided   Single-sided   Double-sided
==============================================================================
Boot Record      Sector 1       Sector 1       Sector 1       Sector 1
                 Track  0       Track  0       Track  0       Track  0
                                Head   0                      Head   0
------------------------------------------------------------------------------
FAT, 1st copy    Sector 2       Sector 2       Sector 2-3     Sector 2-3
                 Track  0       Track  0       Track  0       Track  0
                                Head   0                      Head   0
------------------------------------------------------------------------------
FAT, 2nd copy    Sector 3       Sector 3       Sector 4-5     Sector 4-5
                 Track  0       Track  0       Track  0       Track  0
                                Head   0                      Head   0
------------------------------------------------------------------------------
File Directory   Sector 4-7     Sector 4-7     Sector 6-9     Sector 6-9
                 Track  0       Track  0       Track  0       Track  0
                                Head   0                      Head   0
                                ----------                    ----------
                                Sector 1-3                    Sector 1-3
                                Track  0                      Track  0
                                Head   1                      Head   1
==============================================================================

How to change the status of a file or subdirectory:-

   Refer to the table above and move to the directory sector. Look at the file
entries in the sector. Each file takes up 32 bytes in the directory. The first
8 bytes define the filename and the next 3 bytes define the file type (ie. COM,
EXE, etc). Immediately after the file type is the status or attribute byte.

   Compare the attribute with the numbers below to find the status of that
directory entry. All values are in hexadecimal.

$27   - System file (eg. IO.SYS, MSDOS.SYS), Hidden from DIR command.
        Do not alter this byte.
$20   - Any normal file (eg. COLUMBUS.COM, PCPLUS.BAT). Shown with DIR command.
        To Hide this type of file from DIR command change byte to $22.
        To make Read-Only so that it can't be altered or deleted change to $21.
        To make Hidden and Read-Only change to $23.
$28   - Volume name. Do not alter this attribute.
$10   - Subdirectory name. To hide from DIR command change byte to $12.
        Only first level subdirectories are shown in the directory sectors, so
        if you wish to hide a subdirectory of a subdirectory use the search
        command to find the subdirectory name and then change the attribute.

   I do not have enough space or time to show you how to exploit the full use
of COLUMBUS but I can suggest the following books:-

         ADVANCED MSDOS from Microsoft Press (468 pages) £19.95
         MSDOS BIBLE from Sams-The Waite Group (386 pages) £16.95

   Both these books have detailed information on MSDOS disk structures as well
as lots of other useful information. Both should be available from good
computer shops.