Storage devices can be categorized as magnetic or optical. The most common magnetic storage devices are diskettes, hard disks, high-capacity floppy disks, disk cartridges, and magnetic tape. The primary types of optical storage are compact disk read-only memory (CD-ROM), digital video disk read-only memory (DVD-ROM), CD-Recordable (CD-R), CD-ReWritable (CD-RW), DVD-Recordable (DVD-R), DVD-ReWritable (DVD-RW) and PhotoCD.
Magnetic Storage Devices
Magnetic storage devices work by polarizing tiny pieces of iron on the magnetic medium. Read/write heads contain electromagnets that create magnetic charges on the medium. Diskette drives, also known as floppy disk drives, read and write to diskettes. Diskettes are used most often to transfer files between computers, as a means for distributing software, and as a backup medium. 3.5 inches diskettes are available at present. Before a magnetic disk can be used, it must be formatted – a process that maps the disk's surface and creates tracks and sectors where data can be stored. When a disk is formatted, the operating system creates four distinct areas on its surface: the boot sector, FAT, root folder, and data area.
Hard disks can store more data than diskettes because of their higher-quality media, faster rotational speed, and the tiny distance between the read/write head and the disk's surface. Removable hard disks combine high capacity with the convenience of diskettes.
High-capacity floppy disks are becoming a popular add-on for many computers. They offer capacities up to 250 MB and the same portability as standard floppy disks.
Data cartridges are like small removable hard disks and can store up to 200 GB.
Magnetic tape systems offer slow data access, but because of their large capacities and low cost, they are a popular backup medium.
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.