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 don’t 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. Let’s  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 2-26 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. Let’s assume you created a file that contains all E-4 evaluations for the year 1997 and you named the file DIV-EVAL. It’s 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 year’s DIV-EVAL.98, the following year’s 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,