Optical Storage Devices CD-ROM uses the same technology as a music CD does; a laser reads lands and pits on the surface of the disk. Standard CD-ROM disks can store up to 700 MB. Once data is written to the disk, it cannot be changed.
DVD-ROM technology is a variation on standard CD-ROM. DVDs offer capacities up to 17 GB.
Other popular variations on CD-ROM and DVD-ROM are CD-Recordable, CD-ReWritable, DVD-Recordable, DVD-ReWritable and PhotoCD.
UNIT 3. Operating System
An operating system (OS) is a software program that provides you with the tools (commands) that enable you to interact with the PC.
Most modern operating systems employ a graphical user interface (GUI) with which users control the system by pointing and clicking graphical objects on the screen. A GUI is based on the desktop metaphor. Icons, windows, menus, dialog boxes, and other graphical objects appear on the desktop for the user to manipulate. Applications designed to run under a specific operating system use the same interface elements, so users can see a familiar interface no matter what programs they are using. Some older operating systems, such as DOS and UNIX, use command-line interfaces, which the user controls by typing commands at a prompt.
The operating system manages all the other programs that run on the PC. The operating system also provides system-level services, including file management, memory management, printing, and others, to those programs. Some operating systems, such as Windows, enable programs to share information. This capability enables you to create data in one program and use it again in other programs without recreating it. Modern operating systems support multitasking, which is the capability of running multiple processes simultaneously.
The operating system keeps track of all the files on each disk. To track the location of each file, the operating system maintains a running list of information on each file, in a table that is typically called the file allocation table (FAT). Users can make their own file management easier by creating a hierarchical file system that includes folders and subfolders arranged in a logical order.
The operating system uses interrupt requests (IRQs) to maintain organized communication with the CPU and other pieces of hardware. Each of the hardware devices is controlled by another piece of software, called a driver, which allows the operating system to activate and use the device.
The operating system also provides the software necessary to link computers and form a network.