Using Personal Computers

Section 1: An Introduction to Computers

Part 3: Files, Folders, Disks and Programs


	The term "file" can be confusing to a new computer user. A traditional (paper) "file" is normally a wallet or binder containing several related documents or papers. However, in computer terms, a file is a single document. A "folder" or "directory" (see the next slide) is more closely equivalent to the traditional meaning of the word "file". We'll come back to files in more detail once we've introduced a few more ideas.
	It's a good idea to create folders and subfolders to keep the files on your PC well organised. That way, you can find things more easily, and you are less likely to fill up your hard disk with a clutter of old files that you have "lost" or forgotten about.
	This diagram illustrates the way folders can contain files and other folders. The Windows 3.1 file manager and the Windows 95 Explorer display folders in a similar manner to this. In this example, the folder Work contains two folders, called Reports and Letters. The Letters folder in turn contains two files, called "Letter to Jim" and "Letter to Mary", and two more folders, called 1996 and 1997 for previous years correspondence. The other folders could also of course contain more files and folders which are not illustrated here.
	If your hard disk has not been partitioned, you will only have one letter for your hard disk, C:, but if it has been partitioned, you may have several letters, such as C:, D:, E:, etc. The number of partitions varies depending on how the computer has been set up. Each partition acts like a separate disk drive. If you have got several partitions on your disk, the files which make up Windows itself will normally be on the C: partition. The CD-ROM will normally take the next letter up after all of the hard disk partitions. For example, if you have three partitions on your hard disk, C:, D: and E:, then the CD-ROM will be F:. We'll look at partitions more closely later on in the course
	Disk compression can be used to fit more files on your hard disk. However, these days hard disks are so large and cheap that it is normally not worth considering. You may wish to use it if you have an older computer with a small disk, but you should consider buying a larger hard disk if you can afford it. The software for compressing disks is built into DOS and Windows, should you decide to use it.
	Up to now, we've been looking at the operating system. However, to do something useful, the computer needs some applications, or programs (the two terms mean largely the same thing). Some programs come with the operating system, and computer manufacturers often add a few more if you buy a complete system from them. Other applications must be bought separately and installed. A typical application consists of lots of files. Usually (but not always) most of these will be stored in a folder with the same name as the application. Some files may also be stored in folders belonging to the operating system. Do not move or delete the files belonging to either an application or the operating system - your computer may stop working.
	This diagram attempts to illustrate the relationship between the operating system (Windows), application programs, and data files. Windows is present the whole time you are running the computer (unless you are just running DOS). Application programs are loaded from the disk into memory (RAM) by Windows when you need them, and removed when you close them down. Some (but not all) application programs in turn load data files into memory. For example, when you open a word processing document, Windows first loads the word processing application (for example, Windows Write or Microsoft Word). The word processor then loads the document file so that you can modify it.
	Different types of data file hold different types of information. Some types hold words, some pictures, some sounds etc. Some types of file contain several of these combined together. The information in different file types is stored in different formats - in other words, it is organised differently. Different application programs use different file types. For example, a word processor uses a file type which is different to that used by a drawing program. Sometimes, two different programs will use different formats of data file even if they both do the same job. For example, Microsoft Word and WordPerfect are both word processors, but use different file formats. Some programs can "import" and "export" files that are not in their own format. For example, Microsoft Word can import and export files in WordPerfect format so that users of the two programs can share files. However, this is not always completely successful.
	A Windows 3.1 (or DOS) file name can have up to 8 characters in the name, and up to 3 characters in the extension. The allowed characters are letters, numbers, and some (but not all) or the special symbols on the keyboard. In particular, spaces, dots, commas and slashes (\ and /) are not allowed. You can type upper or lower case characters, but they will all be treated the same. They may be displayed in upper or lower case, depending on the circumstances. The extension indicates the type of file, e.g. .DOC for a word processing document. However: Changing the extension does not change the file type Sometimes the same extension is used for more than one file type. For example, two different word processors with different file formats may both use .DOC as their normal file extension.
	A Windows 95 file name can be up to 254 characters long, including the extension. It can contain upper and lower case characters. However, if you get the case wrong when typing the name of an existing file, Windows will still recognise the name as belonging to that file. For example, if you wished to load the file name in the example above, but typed "SCHOOL MEETING MINUTES.DOC", it would still load it. By default, the extension is only shown for "unregistered" file types. A file type is unregistered if Windows does not "know" what program to use to open that type. For "registered" files, only the name is shown, and the type of file is indicated by the type of icon used. However, you can tell Windows to display the extensions for all files if you prefer. All files with long filenames also have a short filename so that Windows 3.1 and DOS programs can understand them. This is normally the first 6 non-space characters of the name, followed by the tilde (~) character, and then a number (in case there are several files which start with the same first six characters). For example, the short filename for "School Meeting Minutes.doc" might be SCHOOL~1.DOC.
	Windows 3.1 can have lots of different icons for programs in the Program Manager, but it has only has three types of icon for files. However Windows 95 uses a different icon for each type of file, so many different icons can exist. It's even possible to change them or to create your own.

	Windows can display the above information about each file. It can also use this information to help you sort files - for example, you can display files with the most recent first, or search for files created between certain dates. For the date and time information to be the correct, the system clock must be correct.
	The read only attribute can be useful in protecting files against accidental deletion. However, be warned: it does not stop you dragging a file into the Windows 95 recycle bin.
	You will sometimes be asked to type a file path when opening or saving a file, or when installing a program. A file path specifies: The disk a file is on, e.g. C: The folders and subfolders it is in, separated by \ The name and extension of the file For example: C:\DOCS\REPORTS\JANUARY.DOC is a file called JANUARY.DOC in folder REPORTS, which is in folder DOCS, which is on disk drive C. D:\BOOKS.DOC is a file in the root directory of drive D - that is, it is not in a folder. NOTE: The term PATH is also used to refer to the list of directories which are searched to find a program. This will be covered later on in the course.

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