3.3.2 File and Printer Sharing

• Files

• Printers

Files and printers are resources of the computer that are shared in a networking environment, allowing many users to access one drive, file, or printer remotely.

Files

Files may be shared between applications, such as when a graph created in Excel is linked into a Word document. Files may also be shared between users over a network. But, some files will need to be kept private; other users should not be able to access them. To accomplish this, the operating system defines a set of permissions for a file or directory. These permissions, also called Access Control Lists (ACLs), determine who can read, write, or execute the file. Read access allows the user to read the file. Write access allows a user to modify or delete the file. Execute access allows the user to perform special system operations—such as viewing the contents of a directory or executing a program. In Microsoft Windows, you can examine a file's permissions by right-clicking the file icon, clicking Properties on the shortcut menu that appears, and then clicking the Security tab.

Printers

Printers are shared between applications, between users, and even between machines. When a file is to be printed, it is handed off to a part of the operating system called a print server that maintains a queue of print requests. The server processes requests one at a time. As requests come in, they are stored on disk, in a process known as spooling. ("Spool" stands for Simultaneous Peripheral Operation Online). Spooling allows the process issuing the print request to go on to other things; it does not have to wait for the document to complete printing. If the print server can communicate over a network, then print requests can be accepted from other machines. A typical example is a computer lab where all the computers share a single print server. This is more efficient than installing a separate printer on each machine.

3.4 File Systems

A file system is an abstraction for organizing data on mass storage media such as hard drives, floppy disks, and optical disks. The file systems are managed by the operating system of a computer. In this section, you will learn about how files are organized on a Windows operating system, as well as how file systems work.

3.4.1 File Organization

• Files

• Folders

• Drives

• Paths

• Shortcuts

• File Names and Types

One of the main things computers are used for is storing and retrieving information. The information is stored in one or more "files," which in turn are organized into "folders." The Microsoft Windows file system supports four kinds of entities: files, folders, drives, and shortcuts. The figure below illustrates how files are organized from the perspective of a Windows operating system user.

Figure 1 File organization in a Windows operating system

Files

Each file contains some data. When a file is associated with a particular application, such as Microsoft Word, Excel, or Power Point, it is often called a document. Every file has a name. In Windows, file names can be up to 255 characters long and can contain letters, numbers, and certain special characters, including spaces. Although Windows allows use of both uppercase and lowercase letters in a file name, the distinction is ignored by the file system. Thus if you create a file named Friends, you can also access it as friends or FRIENDS or even fRiEnDs. Other operating systems, such as Unix/Linux, are sensitive to capitalization. In these operating systems, the files Friends.txt and friends.txt are different.

Every file also has a set of properties associated with it. The most important property is the file type, which indicates to the operating system what application to use to open the file. Other properties include the size of the file, the date and time the file was created, and the date and time the file was last modified. You can view a file's properties by clicking with the right mouse button the file icon and selecting Properties on the pop-up menu. If you have access to a Windows machine, try this now. Another way to see file types and sizes is to go to the View menu in the Folder window and click Details.