The Operating System

Most Personal Computers run under the MSDOS Operating System. MSDOS being the Microsoft Disk Operating System. It is estimated that almost 10 million machines run under theMSDOS Operating System and some 20,000 or more end-user applications have been published to run with it.

The Operating System is the program which provides organised services to the computer user and the application programs that they wish to use. These services consist mainly of access to the hardware resources such as the disk drives, keyboard, etc.

The Operating System has three main constituents:-

  1. The system files which are hidden. Their function is to perform such basic tasks as reading the keyboard, displaying characters on the screen, opening and closing files etc.
  1. The command interrupter, COMMAND.COM which reads commands typed at the keyboard and attempts to obey them. COMMAND.COM has some simple commands built in - these are known as internal commands.
  1. A series of utility programs covering functions not handled by the internal commands. There are approximately 52 of these commands, the exact number varies between different versions of MSDOS , ranging from COPY to copy files to EDIT the text editor, and many more

Disks and Drives

Because most of your computers Memory (RAM) is temporary, its contents are erased when you switch off the power. You need a place to store the Operating System, application programs and your work. That's where disks come in, you store any information you want to keep onto disks.

There are two types of disk: Floppy disks & Hard disks.

Floppy disks (Diskettes)

A disk is a magnetically coated disk of thin plastic, inside a rigid plastic cover.

You can use Floppy disks to:

You need only format a disk once. After that, you can use the disk again and again without having to reformat it. Formatting a disk you have previously used erases any data on the disk, so only reformat a disk if you are sure you don't need any of the data on it.

Choosing disks

Diskettes come in various forms, so it is important to choose diskettes that match the type of diskette drive installed in your computer. Several different types are available :

It should be noted that :-

Hard disks

A Hard disk is a disk that is enclosed in a permanently sealed metal housing. Hard disks are better than Floppy diskettes in two main respects:

Working with Files and Directories

This section introduces you to two of the most fundamental aspects of using you computer - working with files, and organising those files into directories.

Files

A file is simply a collection of information that you store on a disk or diskette. The normal way to create a file is to run an application. For example, when you use a word processing application to write a letter, you save the letter by storing it as a file.

In general, each file must have a unique name. However, two files can share the same name provided that they are on different disks, or in different directories.

A file name has two parts: the filename itself and an extension. In this example:

RECIPE.DOC

RECIPE is the filename and DOC is the extension. Note the FULL STOP between the two parts of the name. When a filename has an extension, the two parts of the name are separated by a full stop.

Filenames

Choose filenames with care, as a good name will help you to remember what kind of information is in the file. A filename may contain up to eight characters.
For example:

PDL, README, 4JULY96, MEMO_MAY

The only characters you cannot use in filenames are:

" / \ [ ] < > + = ; : , ? * { }
Spaces are also not permitted. If in any doubt use only letters or numbers.

Some filenames to avoid

There are some filenames that you should avoid when naming files because your computer reserves them for special uses.

AUX, COM1 or COM2The internal name of a device connected to a Serial Port.

CONThe internal name of data sent to the keyboard or screen.

LPT1, LPT2, LST or PRNThe internal names for the printer connected to the Parallel port.

Extensions

Use extensions to make your filenames more descriptive. For example you could add the extension DOC to every document you write. Then when displaying a list of the files on your disk, you can tell quickly which files contain documents.

NOTE:- Some applications add their own unique extensions, these should NOT be altered. If you do the program may not be able to use them. An extension may contain up to three characters.

These are all valid extensions:

A , TXT, 88, B_2

The same characters are invalid as for filenames, see last page.

Taking care with extensions

There are some extensions to which you computer attaches a special meaning. Only add these extensions to a file if you are sure the file performs the correct function:

BAK A backup file. When you save a file, the previous version of that file MAY be automatically saved as a backup with a BAK extension.
COM or EXE A program or MSDOS /application file
$$$ An incorrect or compressed file.

Directories

One way of organising the files on your computers Hard disk is to put them in different directories. Directories enable you to arrange your files in whatever way you want and get files you need quickly.

Every disk has one basic directory, called the ROOT directory, which you create automatically when you format the disk. As well as putting files in this directory, you can also create directories inside it. Each subdirectory can hold files, and in turn, further subdirectories. The number of subdirectories on a disk is limited only by the amount of storage space on the disk.

You can visualise a system of directories as an upside-down tree, with the root directory at the top and the subdirectories branching off it.

Pathnames

If you use directories, you must tell your computer where to look for any particular file you want to edit. You do this by specifying the pathname of the file.

A pathname is a sequence of directory names followed by a filename. Each directory name is separated from the previous one by a backslash ( \ ). For example the pathname for a file called MEMO.DOC could be :-

C:\USER\PETER\MEMO.DOC

Part 1 Questions

  1. What do the Operating System services consist of ?
  2. Give two examples of MSDOS commands.
  3. What must you do first to a new Floppy diskette?
  4. What is the most common size and capacity of a Floppy diskette?
  5. Give one way in which Hard disks are superior to Floppy disks.
  6. What is wrong with each of the names of these files?
  7. Give the full pathname for MEMO.DOC
    8. C:\
|
|__ DOS\
|
|__DATA\
|       |
|       |__ OFFICE\
|               |
|               |__ MEMO1.DOC
|               |
|               |__MEMO.DOC
|
|__ WP51\
  8. In the following command - COMMAND.COM
Return to DOS menu

E-Mail your answers to:-

dos@butterwick0.freeserve.co.uk