How to Use the DOS BACKUP Command
by the Disk Doctor


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Copyright (C) 1987,  the Disk Doctor.

First published in the Rochester (PC)^3 News:
  Picture City PC Programming Club
  PO BOX 20342
  Rochester, NY 14602
The Disk Doctor may be contacted at this
address, or via CIS [73147,414].

This material may be reproduced for internal
use by other not-for-profit groups, provided
this copyright notice is included.
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[Don't let a mistake or a power glitch
wipe out all your data.  Regular,
intelligent backups are the best
protection against all forms of disk
damage.]


A backup is a copy of a program or data
that is made to safeguard against damage
to the program or data by accidental
means.

This backup procedure was written with IBM
Personal Computers as a basis.  All
commands referenced in this procedure are
found in the DOS manual.  The reasons for
backing-up disks and files relate to any
brand of personal computer.



Why do Backups?

Your programs and data disks should be
backed up because accidents will happen.
Your disks may be damaged from incidents
beyond your control.  If you have
established a plan for backing up your
data and programs then when something does
happen you are protected.  If you wait
until something happens to your data then
it will be too late. You can't use a
backup that you don't have.

"If you can't afford to lose it, you can't
afford not to back it up".


What Should I Backup?

Everyone who uses a personal computer
should backup the data and programs that
are used.


Purchased Programs:

Used on a Hard Disk (PC-XT or PC-AT)

Programs that are copied to a hard disk
and run from the hard disk do not need to
be backed up. You already have backed up
the program by initially copying it to the
hard disk.


Used on a Two Floppy Diskette System (PC)

Programs that are run on a PC using one or
more floppy diskettes should be backed up
to protect against damage to the program
disk. Most purchased, copy protected
software will come with an additional copy
of the program disk or a special procedure
for making a backup. If it comes with the
additional copy than a backup is not
necessary. You should read the directions
that accompany purchased software very
carefully to insure that you are backing
up the software correctly.




User Written Programs

All user written programs should be backed
up whenever changes are made.



Data Files and Disks

All data files should be backed up on a
regular and consistent basis to safeguard
against loss of data.  The frequency of
back ups depends on the individual
application.



How Often Should I Backup?

When to backup data disks depends upon the
difficulty of reconstructing the data once
it is lost and the need to reconstruct the
data when it is lost.  Some variables that
will influence the decision of when to
backup a data disk are:

1. How often are changes made ?

2. How much data was changed ?

3. Are other sources of the data readably
  available ?

4. How important is the data?

5. How much time will you spend
  reconstructing the data?

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How to Do a Backup?

There are several ways to backup data
depending on the type of system you are
using.  The following commands are for IBM
or MS-DOS computers.


COPY

This is a DOS command that is used to make
copies of files.  It can be used to backup
a floppy disk by placing a formatted disk
in drive B: (the "target") and inserting
the disk you are going to make a backup of
in drive A: (the "source").  You then
issue the command

    "COPY A:*.*  B:".

This command will copy all files from the
current directory (see your DOS manual for
more on directories) on the disk in drive
A:, appending them to the disk in drive
B:, if there is room.

This command may also be used to make
copies of files from a hard disk to a
floppy disk.  The command is issued from
the directory containing the files that
are to be backed up.  For example,

   COPY *.* A:

This would copy all files in the current
directory of the hard disk to the floppy
disk in drive a, if there is room on the
floppy disk in drive a.

A verify option is available for use with
this command.  This insures that all files
were written to the disk correctly.

More information on this command can be
found in the DOS manual.



DISKCOPY

This is a DOS command that can be used to
make a backup of a floppy diskette. Place
a disk in drive B: (the "target") and the
DOS disk  in drive A:, then issue the
command



DISKCOPY A: B:

You will be prompted to place your source
disk in drive A:, (the disk you want to
copy).  ALL FILES ON THE TARGET DISK WILL
BE LOST when you execute this command.
This command will make an exact copy of
the source disk.  More information on this
command can be found in the DOS manual.

It is a good idea to use a write protect
tab on the disk you wish to copy.  It will
prevent the accidental erasure of a data
disk if you make a mistake when issuing
the command.



DISKCOMP

This command is used to compare two
diskettes after using the diskcopy
command.  It is a good practice to compare
the original to the copy after using the
diskcopy command.  This command is not
meaningful when used after the copy
command.



BACKUP (FOR Hard Disks -- PC-XTs AND ATs)

This command can only be used for backing
up files from a hard disk. You should have
plenty of empty, formatted disks available
before issuing this command.

To determine the number of disks
necessary, issue a directory command (DIR)
for the hard disk.  At the end of the
listing of files you will be shown the
available bytes.  If you have a 10 Meg
hard disk, subtract the available bytes
figure from 10,500,00 and divide by
350,000 to arrive at an approximate number
of disks necessary.

For example, if the system indicates that
there are 6,500,000 bytes available then
you subtract 6,500,000 from 10,500,000 to
arrive at a figure of 4,000,000.  Then
divide this by 350,000 to arrive at a
figure of 11.4 or 12 disks.

This figure represents the maximum number
disks necessary to backup the hard disk.
The backup command has several options
that let you choose which files are to be
backed up so you may not need all the
disks. It important to have enough disks
available before you start.  If you don't
then you have to start over from the
beginning.

Once you have determined the number of
disks needed to perform the backup you
should number them, starting at 1. This is
important, if you have to restore these
files to the hard disk you must do it in
the same order that you backed them up.

When you have the necessary number of
disks available issue the command

     BACKUP C:\ /s A:

The letter (C:) must be the drive
indicator of your hard disk. The "\" says
to start at the ROOT directory.  The "/s"
indicates that you want to backup all
subdirectories of the ROOT directory.  The
"A:" represents the  target drive that you
are backing up the files to.

There are many switches that may be used
with this command ("/s" is an switch).
These options allow you to backup only
those files that have been changed since
the last backup.  Another option allows
you backup files created since a specific
date. A third option lets you append files
to a previous backup disk.  Please refer
to you DOS manual to get an explanation of
these switches.


RESTORE

This command is used to restore your files
to the hard disk in the event that the
hard disk has been damaged. You should
refer to the DOS manual for more
information about this command.  To use
this command you must have "backed up your
hard disk by using the "backup" command.




Final Notes

There are a number of commercial and
public domain utilities that improve on
the DOS BACKUP command.  This article
describes only those commands in native
DOS.

If you exercise good judgement in backing
up your files you will save yourself time
and aggravation if something does happen
to your disks.

Your individual situation will dictate how
frequently you should backup your files.
For some people it may be once a day, for
others once a week and still for others
once every two weeks.

Backups take time, but compare it with the
time it will take to reconstruct the disks
with no backup.

Take care of your backup diskettes.  They
won't do you any good if they are lost or
damaged when you go to use them.

The single best insurance against any type
of disk problem is frequent, intelligent
backups.

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