working with, and how to properly logoff the system at
the end of their work day are also important parts of
their job.
TAPE RETENTION
A restricted retention period has been established to
prevent permanent physical damage to magnetic tapes,
especially tapes that are stored for long periods of time,
such as history tapes. This provides for all magnetic
tapes to be cleaned, possibly certified, and repacked at
prescribed time intervals. This procedure eliminates
such problems as oxide sticking, debris embedment,
and edge deformation caused by tape pack shifts inside
the reel.
Initially, an on-site save tape retention period
should be restricted to a maximum of 90 days, with only
one 90-day extension.
After 180 days, you should
notify the user indicating that the tape should be copied
(and verified) onto a recently cleaned tape, thus freeing
the original tape to be tested for accuracy. The retention
period for off-site tapes should initially be 180 days,
with one 30-day extension.
FILE AND DISK MANAGEMENT
File and disk management are other areas where
your knowledge will help users. They probably dont
know the agony of delete or the problems sometimes
caused by very large files. Think about what you have
learned regarding file management. How to name files.
How to cleanup files. How to back up files. When to
back up files. Where and how to physically store files.
How to protect files. How to organize files on disks.
Lets examine some of the considerations for setting up
files and file management procedures for
microcomputers: naming files, disk file organization,
and file backup. We will be using DOS as the operating
system for the examples in this section.
Naming Files
Every newly created file must be given a file name
if it is to be stored (written and given an address) on
disk. When the operating system looks for a filename,
it looks up the address in its address book, the
directory.
The directory is maintained in a fixed
location on every disk.
Every operating system will have a system for
naming files. In DOS, file names have two parts. The
first part, the primary file name, names the file and can
be from one to eight characters in length. The second
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part, called the file name extension, is optional, and can
be from one to three characters. While the extension is
optional, the primary part of the file name is NOT. An
extension cannot name a file, it can only be used to
further qualify or describe a file. If both parts are used,
they must be separated by a period, for example,
TELECOMM.TP7. To name a file (including its
extension), you may use any combination of the
following characters: the letters A through Z (upper and
lower case), the numbers 0 through 9, the following
special characters: $, #, !, %, ( ), -, { }, _, and the left and
right apostrophe.
Why would you want to use an extension? you
might ask. Lets assume you created a file that contains
all E-4 evaluations for the year 1997 and you named the
file DIV-EVAL. Its a perfectly good and valid name
under DOS. However, it is entirely possible you would
want more than one file called DIV-EVAL, considering
the years that follow. In this case, you might want to use
the option of adding a file name extension. For
example, you could label the 1997 evals DIV-EVAL.97,
the next years DIV-EVAL.98, the following years DIV-
EVAL.99, and so on. In this case, the years 97,98, and
99 are the extensions.
Some extensions have special meanings in DOS
and are either created by DOS or assume the file
contains a special type of program or data. For this
reason, use extreme caution and avoid using file
extensions defined by the program or operating system
you are using.
Examples of extensions assigned by
DOS are as follows:
COM, EXE, SYS, BAT File extensions such as
COM(mand), Executable), SYS(tem), and BAT(ch)
contain executable code. That is, the code is actually
understood by the hardware when programs are run.
BAK When opening a text file, the DOS program
automatically makes a backup copy with the
extension BAK.
BAS BAS refers to a source program written in
the BASIC language.
COB COB refers to a source program written in
COBOL.
HEX HEX refers to a special type file where all
information has been stored in HEXADECIMAL
format.
Various applications software packages
automatically add an extension.
For example,
ENABLE adds WPF, DBASE adds DBF, NDX,