• Storage devices hold data, even when the computer is turned of.

• The physical material that actualy holds data is caled a storage medium. The surface of a floppy disk is a storage medium.

• The hardware that writes data to or reads data from a storage medium is caled a storage device. A floppy disk drive is a storage device.

• The two primary storage technologies are magnetic and optical.

The primary types of magnetic storage are:

• Disketes (floppy disks)

• Hard disks

• High-capacity floppy disks

• Disk cartridges

• Magnetic tape

The primary types of optical storage are:

• Compact Disk Read-Only Memory (CD-ROM)

• Digital Video Disk Read-Only Memory (DVD-ROM)

o CD-Recordable (CD-R)

• CD-Rewritable (CD-RW)

• PhotoCD


– How Magnetic Storage Works

• A magnetic disk’s medium contains iron particles, which can be polarized—given a magnetic charge—in one of two directions.

• Each particle’s direction represents a 1 (on) or 0 (of), representing each bit of data that the CPU can recognize.

• A disk drive uses read/write heads containing electromagnets to create magnetic charges on the medium.


• Before a magnetic disk can be used, it must be formated—a process that maps the disk’s surface and determines how data wil be stored.

• During formating, the drive creates circular tracks around the disk’s surface, then divides each track into sectors.

• The OS organizes sectors into groups, caled clusters, then tracks each file’s location according to the clusters it occupies.

-Disk Areas

When a disk is formated, the OS creates four areas on its surface:

• Boot sector – stores the master boot record, a smalL program that runs when you first start (boot) the computer.

• File alocation table (FAT) – a log that records each file’s location and each sector’s status

• Root folder – enables the user to store data on the disk in a logical way

• Data area – the portion of the disk that actualy holds data


• Diskete drives,alsoknown as floppy disk drives, read and write to disketes (caled floppy disks or floppies).

• Disketes are used to transfer files between computers, as a means for distributing software,and as a backup medium.
• •Disketes come in two sizes: 5.25-inch and 3.5-inch.

-Hard Disks

• Hard disks use multiple platers, stacked on a spindle. Each plater has two read/write heads, one for each side.

• Hard disks use higher-quality media and a faster rotational speed than disketes.

• Removable hard disks combine high capacity with the convenience of disketes.

-Disk Capacities

• Disketes are available in diferent capacities, but the most common store 1.44 MB.

• Hard disks storelarge amounts of data. New PCs feature hard disks with capacities of 10 GB and higher.

-Other Magnetic Storage Devices

• High-capacity floppy disks ofer capacities up to 250 MB and the portability of standard floppy disks.

• Disk cartridges are like smal removable hard disks, and can store up to 2 GB.

• Magnetic tape systems ofer very slow data access, but provide large capacities and low cost.


-How Optical Storage Works

• An optical disk is a high-capacity storage medium.
• An optical drive uses reflected light to read data.
• To store data, the disk’s metal surface is covered with tiny dents (pits) and flat spots (lands), which cause light to be reflected diferently.
• When an optical drive shines light into a pit, the light cannot be reflected back. This represents a bit value of 0 (of). A land reflects light back to its source, representing a bit value of 1 (on).


• In PCs, the most commonly usedoptical storage technology is called Compact Disk Read-Only Memory (CD-ROM).

• A standard CD-ROM disk can store up to 650 MB of data, or about 70 minutes of audio.

• Once data is writen toa standard CD-ROM disk, the data cannot be altered or overwriten.

-CD-ROM Speeds and Uses

• Early CD-ROM drives were caled single speed, and read data at a rate of 150 KBps. (Hard disks transfer data at rates of 5 – 15 MBps).

• CD-ROM drives now can transfer data at speeds of up to 7800 KBps. Data transfer speeds are geting faster.
• CD-ROM is typicaly used to store software programs. CDs can store audio and video data, as wel as text and program instructions.


• A variation of CD-ROM is caled Digital Video Disk Read-Only Memory (DVD-ROM), and is being used in place of CD-ROM in many newer PCs.

• Standard DVD disks store up to 9.4 GB of data—enough to store an entire movie. Dual-layer DVD disks can store up to 17 GB.

• DVD disks can store so much data because both sides of the disk are used, along with sophisticated data compression technologies.

-Other Optical Storage Devices

• A CD-Recordable (CD-R) drive lets you record your own CDs, but data cannot be overwriten once it is recorded to the disk.

• A CD-Rewritable (CD-RW) drive lets you record a CD, then write new data over the already recorded data.

• PhotoCD technology is used to store digital photographs.


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