CSC 134 Lecture outline
Chapter 6
Chapter 6
Secondary Storage
6.1 Floppy Disks
Floppy disk, often called a diskette or simply a disk, is a removable flat
piece of mylar plastic packaged in a 3.5-inch plastic case.
3.5-inch floppy disks—1.44 megabytes
Zip disks—100 megabytes
SuperDisks—120 megabytes
HiFD disks—200 megabytes
6.2 Hard Disks
Hard disks are thin but rigid metal platters covered with a substance
that allows data to be held in the form of magnetized spots.
A head crash happens when the surface of the read/write head or
particles on its surface come into contact with the surface of the hard-
disk platter, causing the loss of some or all of the data on the disk.
There are two types of hard disks—nonremovable and removable.
Hard-Disk Technology for Large Computer Systems
Three types of secondary-storage devices are available for large
computers:
Removable packs: A removable-pack hard-disk system contains
6–20 hard disks, of 10.5- or 14-inch diameter, aligned one above the
other in a sealed unit. Capacity varies; some packs range into the
terabytes.
Fixed-disk drives: Fixed-disk drives are high-speed, high-capacity
disk drives that are housed (sealed) in their own cabinets.
RAID storage system: A RAID (redundant array of inexpensive
disks) storage system, which consists of two or more disk drives
within a single cabinet or connected along a SCSI chain, sends data
to the computer along several parallel paths simultaneously.
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CSC 134 Lecture outline
Chapter 6
6.3 Optical Disks: CDs & DVDs
An optical disk is a removable disk, usually 4.75 inches in diameter
and less than one-twentieth of an inch thick, on which data is written
and read through the use of laser beams. Some optical disks are used
strictly for digital data storage, but many are used to distribute
multimedia programs that combine text, visuals, and sound.
Among the types of optical disks are the following:
CD-ROM—for reading only: CD-ROM (compact disk read-only
memory)
CD-R—for recording on once: CD-R (compact disk–recordable)
disks
CD-RW—for rewriting many times: A CD-RW (compact disk–
rewritable) disk
DVD-ROM—the versatile video disk: A DVD-ROM (digital versatile
disk or digital video disk, with read-only memory)
6.4 Magnetic Tape
Magnetic tape is thin plastic tape coated with a substance that can be
magnetized. Data is represented by magnetized spots (representing 1s)
or nonmagnetized spots (representing 0s).
6.5 Smart Cards
Smart cards: A smart card looks like a credit card but contains a
microprocessor and memory chip. When inserted into a reader, it
transfers data to and from a central computer. Smart cards can be
used as telephone debit cards.
Optical cards: Optical cards are plastic, laser-recordable, wallet-
type cards used with an optical-card reader.
6.6 Flash Memory Cards
Flash memory cards, or flash RAM cards, consist of circuitry on credit-
card-size cards that can be inserted into slots connecting to the
motherboard. Flash memory cards are not infallible. Their circuits wear
out after repeated use, limiting their lifespan. Still, unlike conventional
computer memory (RAM or primary storage), flash memory is
nonvolatile.
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CSC 134 Lecture outline
Chapter 6
6.7 Online Secondary Storage
If the network computer or thin-client computer actually becomes as
popular as its promoters hope, the Internet itself will become, in effect,
your hard disk. When you sign up with a service, you usually download
from a Web site free software that lets you upload whatever files you
wish to the company’s server. For security, you are given a password,
and the files are supposedly encrypted to guard against anyone giving
them an unwanted look.
6.8 Future Developments in Secondary Storage
Greater Secondary Storage: Higher-Density Disks
Higher densities allow disks to be packaged in smaller sizes. In 2000,
IBM tripled the capacity of its silver-dollar-size removable hard drive
from 340 megabytes to 1 gigabyte. The Microdrive, as it’s called, is
designed for digital cameras, MP3 players, and handheld PCs.
Molecular Electronics: Storage at the Subatomic Level
Holograms as storage: A hologram is a three-dimensional picture
created by two lasers. Dark and light areas of the hologram in a crystal
could be used to code binary information. In the future, holograms could
replace not only hard-disk drives but also memory chips.
Molecular magnets as storage: Researchers have succeeded in
creating a microscopic magnet, one molecule in size, derived from a
special combination of materials (manganese, oxygen, carbon, and
hydrogen).
Subtomic lines as storage: Physicists at NEC in Tokyo used a tool
called a scanning tunneling microscope (STM)—to paint and erase tiny
lines roughly 20 atoms thick.
Bacteria as storage: Scientists have reported research involving use of
bacteria to store data in three dimensions.
The Age of “Storewidth”
The arrival of broadband communication is sure to exacerbate the demand for
storage, “with billions of bytes of digital video and graphical data begging for
storage space,” suggests one account. Technology guru George Gilder
already has a name for the future kind of storage: storewidth.
