time. Instead, you must look at each subdirectory to see what is in that one. If E5 Christmas wants to see what files are in the subdirectory SUPPLY, she would use the DOS  command  to  change  the  directory  name  to SUPPLY  and  then  display  its  directory  (figure  2-18, example A). As the number of files on a disk increases, so does the need to have a disk that is well-organized. A well- organized disk can save you a considerable amount of time  and  frustration  in  locating  files.  As  computer specialists, we know this is true and of great importance, but to the uninformed or new user who has not been properly  trained,  disk  management  may  seem  very cumbersome and time consuming. Some users may not even be aware that they can organize their files on disk, and that’s where you come in. How can you help users create  and  use  a  tree-structured  directory?  you  might ask. Whenever  you  format  a  disk,  a  single  directory called a root directory is created. You can then instruct DOS  to  create  or  MaKe  other  DIRectories,  using  a command such as MKDIR or just plain MD. These are called subdirectories. Further, a subdirectory can have other  subdirectories.  Directories,  regardless  of  their level,  are  given  names  just  like  any  other  files.  DOS keeps track of each directory the same way it does your files. Using various DOS file handling commands, you can create (MKDIR or MD), change (CHDIR or CD), and   remove   (RMDIR   or   RD)   directories   and subdirectories. To move through the tree structure (UP or   DOWN),   you   must   issue   commands   that   use   a path name. A path name is a list of the directory(ies) (which   might   end   with   a   file   name) that   DOS Figure  2-18.—Examp1es  of  files  in  subdirectories. 2-28 must  follow  to  find  a  given  directory/subdirectory  or file  name.  In  example  B  in  figure  2-18,  to  locate  the file   named   DIN-MENU.DLY,   the   path   is \CHRISTMAS\FOODSERV\DIN-MENU.DLY. Once   you   have   grouped   related   files   into   a subdirectory, you can act on them as a unit. The DOS file-handling  commands  can  be  applied  to  an  entire subdirectory of files in a single stroke. For example, you can issue commands to copy, print, or delete all the files in a subdirectory as easily as you can for a single file. Other files on the same disk, but in different directories go   unused   and   undisturbed.   Subdirectories   are especially   helpful   when   working   with   hard   disks because of their large storage capacities. To learn more about DOS directory structures and commands,   read   the   DOS   reference   guide   that accompanies the DOS software. Backing Up Files You have heard it before, and you are going to hear it again here: BACKUP your programs and data files. If you don’t, you will eventually lose all or part of your data, and the only person you can blame is yourself. Data can be lost or damaged in a number of ways. Common  causes  of  data  loss  are  power  surges  and drops, power failures, and user errors. User errors top the list. Less common but potentially disastrous are fire, theft, vandalism, and natural disasters. How often have you come close to erasing a file or formatting a floppy or hard disk by accident? Probably more times than you care to admit. No matter how many precautions you take, you can’t prevent all the potential ways data can be lost. You can certainly reduce their adverse effects by backing up your files on a regular basis. When working with data files, you will want to back them up at least on a daily basis either to tape, diskette, or to another hard disk. For our example, we will use two diskettes. A technique referred to as the odd/even backup uses two diskettes. Label one diskette as odd and the other as even. When you make your backups, use  the  odd  diskette  on  odd  days,  and  use  the  even diskette on even days. This pays off when you find that errors were inadvertently made to a file the day before, and you backed-up that file onto your backup diskette. With this system, you can go back 2 days if needed. No  matter  how  many  backups  you  make  (two, three, or one for everyday of the week) or what method you use to make them, they are worthless if they are