Storage Technology

Storage Technology

•          Storage, input and output devices are called peripheral devices because they are outside the main computer system unit.

Secondary (Auxiliary) Storage Technology

•          Secondary storage is used for relatively long term storage of data outside the CPU.

•          Secondary storage is nonvolatile and retains data even when the computer is turned off.

•          The most technologies are magnetic disk, optical disk and magnetic tape.

Storage

•          What is storage?

•          Holds data, instructions, and information for future use

            •          Storage medium is physical material used for storage

            •          Also called secondary storage

•          How does volatility compare?

         •          Storage medium is nonvolatile—contents retained when power is off

         •          Memory is volatile—holds data and instructions temporarily

		ON	OFF
Volatile	Screen Display	Display appears	Display disappears
	Memory (most RAM) (chips on motherboard)	Data and instructions available to user	Data and instructions erased
Non Volatile	Storage Medium (floppy disks, Zip disks, hard disks, CDs)	Contents available to user	Contents retained

Magnetic disk

•          There are two kinds of magnetic disk:

–         floppy disks

–         hard disks

•          Magnetic Disks permit direct access to individual records so that data stored on the disk can be directly accessed regardless of the order in which the data were originally recorded.

•          Disk storage is often referred to as a direct access storage device (DASD).

What is a floppy disk?

•          Portable, inexpensive storage medium (also called diskette)

•          Thin, circular, flexible film enclosed in 3.5” wide plastic shell

•          What is a floppy disk drive?

•          Device that reads from and
writes to floppy disk

•          One floppy drive, named drive A

•          Also called secondary storage

•          What is a hard disk?

  •    High-capacity storage

   •    Consists of several inflexible, circular platters that store items electronically

   •    Components enclosed in airtight, sealed  case for protection

•          What are tracks and sectors?

               Track is narrow recording band that forms  full circle on disk. Sector stores up to 512 bytes of data.

 Optical Disk

•    Also called compact disks or laser optical disks, used laser technology to store data at densities many times greater than those of magnetic disks.

•          The most common optical disk system used with PCs called CD-ROM (compact disk read only memory).

•          CD-ROM is read-only storage.

What are optical discs?

Ø  Flat, round, portable metal discs made of metal, plastic, and lacquer

Ø  Can be read only or read/write

Ø  Most PCs include an optical disc drive

Ø  How is data stored on an optical disc?

Ø  Typically stored in single track

Ø  Track divided into evenly sized sectors that store items

Ø  WORM (write once/read memory) or CD-R (compact disk-recordable) optical disk systems allow users to record data only once on an optical disk.

Ø  New CD-RW (CD-Rewritable) technology has been developed to allow users to create rewritable optical disks.

Ø  Digital-video disks (DVDs) also called digital versatile disks are optical disks the same size as CD-ROMs but of even higher capacity (minimum of 4.7 gigabytes of data).

Ø  What is a DVD-ROM (digital versatile disc-ROM or digital video disc-ROM)?

Ø  High capacity disc capable of storing 4.7 GB to 17 GB

Ø  Must have DVD-ROM drive or DVD player to read DVD-ROM

Ø  Stores databases, music, complex software, and movies

Ø  How does a DVD-ROM store data?

Ø  Two layers of pits are used, lower layer is semitransparent so laser can read through

Ø  Some are double-sided

Ø  Blu-Ray discs currently have a storage capacity of up to 27 GB

DVD-ROM STORAGE CAPACITIES
Slides	Layers	Storage Capacity
1	1	4.7 GB
1	2	8.5 GB
2	1	9.4 GB
2	2	17 GB

Magnetic Tape

•          Magnetic tape is an older storage technology that still used for secondary storage of large volumes of information.

•          The principle advantages

–         its inexpensiveness, its relative stability and its ability to store very large quantities of information.

•          The disadvantages its sequentially stored data and its relative slowness compared to the speed of secondary storage media

Tape

•          What is tape?

•          Magnetically coated plastic ribbon capable of storing large amounts of data at low cost.

•          Primarily used for backup.

PC Cards

•          What is a PC Card?

            •          Adds capabilities to computer.

            •          Credit-card-sized device commonly used in notebook computers.

 

PC CARDS
Category	Thickness	Use
Type 1	3.3 mm	RAM, SRAM, flash memory
Type 2	5.0 mm	Modem, LAN, SCSI, sound, TV turner, hard disk, or other storage
Type 3	10.5 mm	Rotating storage such as a hard disk