 |  Using Information Technology: A Practical Introduction to Computers and Communications, 5/e Brian K. Williams
Stacey Sawyer
HARDWARE THE CPU & STORAGE: How to Buy a Multimedia Computer System
Web Summary- Microchips, Miniaturization, & Mobility. Computers used to be made
from vacuum tubes. Then came the tiny switches called transistors,
followed by integrated circuits, which embody solid-state technology.
Solid state means that the electrons are traveling through solid material-in
this case, silicon, an element that is widely found in clay and sand
and that is a semiconductor, material whose electrical properties are
intermediate between a good conductor of electricity and a nonconductor of
electricity. Integrated circuit chips, or microchips, are printed and
cut out of "wafers" of silicon. The microcomputer microprocessors,
which process data, are made from microchips. They are also used in other
instruments, such as phones and TVs.
- The System Unit. The basis of the processing part of the computer,
the system unit, is the binary system, which has only 1 and 0. These
two digits, called bits, correspond to the on and off states of electricity
used in computers. A group of 8 bits, called a byte, represents one
character in the computer. Storage capacities are expressed in multiples of
bytes: about 1000 bytes = 1 kilobyte; about 1 million bytes = 1 megabyte;
about 1 billion bytes = 1 gigabyte; about 1 trillion bytes = 1 terabyte;
about 1 quadrillion bytes = 1 petabyte. Letters, numbers, and special
characters are represented within a computer by binary coding schemes,
such as ASCII, the code most widely used in microcomputers; EBCDIC,
used with large computers; and Unicode, a subset of ASCII that uses
16 bits for each character. A parity bit is an extra bit attached to
the end of a byte for purposes of checking for accuracy. Computers each have
their own type of machine language, a binary-type programming language
that the computer can run directly, which is why one type of computer can't
run the software from another type of computer.
The system unit, or case, houses the motherboard, processor
chip, memory chips, and power supply. The system unit also includes
storage devices, such as disk drives, which are housed on shelves called bays.
The motherboard contains sockets for expansion-for adding new components,
such as video cards -- or upgrading -- for changing to more powerful
components, such as more memory chips. To protect it from damage from too
much or too little power, a computer should be plugged into a surge protector
or voltage regulator and also into a UPS, a battery-operated
device that temporarily provides electricity if there is a power failure.
The microprocessor: The most fundamental part of the motherboard,
the microprocessor, is the miniaturized circuitry storing the program instructions
that manipulate data into information. Two architectures for microprocessors
are CISC chips, used mostly in PCs and mainframes, and RISC chips,
used mainly in workstations. Most personal computers today use either Intel-type chips for PCs (made by Intel, AMD, Cyrix, and others for Compaq, Dell,
Gateway, Hewlett-Packard, and IBM) and Motorola-type chips (made by
Motorola for Apple Macintosh computers). The speed of a microprocessor is determined by its system clock. For
microcomputers, processing speeds are measured in megahertz (million
cycles per second) or gigahertz (billion cycles). For workstations,
such speeds are measured in MIPS (millions of instructions per second); for
supercomputers, in flops (floating-point operations per second); and for all
computers, in fractions of a second (milliseconds, microseconds, nanoseconds,
and picoseconds). Another measure, word size, is the number of bits a computer
can process at any one time, with 64 bits being faster than 32 bits. A processor, also called a CPU (central processing unit), follows
the instructions of the software (program) to manipulate data into information.
The CPU consists of the control unit, which deciphers each instruction
stored in it and then carries it out, and the arithmetic logic unit
(ALU), which performs arithmetic and logical operations. Both the control
unit and the ALU contain registers, high-speed storage areas that temporarily
store data during processing. Data transmission within the CPU and between
the CPU and other components of the motherboard is by means of electrical
roadways called buses. Memory: Also on the motherboard are memory chips, of which there
are four types: RAM, ROM, CMOS, and flash. (1)
RAM (for random access memory) chips temporarily hold software instructions
and also data before and after processing by the CPU. RAM is volatile; its
contents are lost when the power goes off. Three types of RAM chips are
DRAM, which must be constantly refreshed by the CPU or it will lose
its contents; SDRAM, which is faster than DRAM; and SRAM,
also faster than DRAM and able to retain its contents without being refreshed
by the CPU. RAM chips often appear on memory modules -- SIMM
has chips on one side, DIMM has chips on both sides -- which can
be plugged into expansion slots on the motherboard. (2) ROM (for
read-only memory) chips contain fixed start-up instructions. (Read means
to transfer data from an input source to the CPU or memory; write means
to transfer data from the CPU or memory to an output device.) A variant
is PROM, a ROM chip that allows users to load read-only programs
and data, although only once. (3) Battery-powered CMOS chips don't
lose their contents when the power is turned off; this quality makes them
useful for holding times and dates. (4) Flash memory chips can be
erased and reprogrammed more than once. The processor searches for data or program instructions in the following
order: first level 1 cache, then level 2 cache, then RAM, then hard disk (or
CD-ROM). Cache temporarily stores instructions and data that the processor
is likely to use frequently, thereby speeding up processing. Level 1 cache
is built into the processor chip; level 2 cache resides outside the
processor chip and consists of SRAM chips. Virtual memory is hard-disk
space used to extend the capacity of RAM. Ports and cables: A port is a connecting socket on the outside
of the system unit into which are plugged different kinds of cables. Six types
of ports are as follows: (1) Serial ports transmit bits one after the
other, or slow data over long distances. (2) Parallel ports transmit
8 bits simultaneously, or fast data over close distances, as to printers.
(3) SCSI ports transmit 32 bits simultaneously in a daisy chain of
up to seven devices linked in a series. (4) USB ports are general-purpose
ports that transmit data to up to 127 devices in a daisy chain. USB permits
Plug and Play, which allows peripheral devices and expansion cards
to be automatically configured while they are being installed. (5) Dedicated
ports exist for special purposes, as for the keyboard and mouse. (6) Infrared ports enable cableless connection with infrared devices, as between the
computer and some printers. Expandability -- buses and cards:Closed architecture means
a personal computer has no expansion slots; open architecture means
it does. Expansion slots are sockets on the motherboard into which
may be plugged expansion cards, circuit boards that provide more memory
or that control peripheral devices. Expansion slots are connected to the CPU
by expansion buses, such as ISA, the oldest and slowest at 8
or 16 bits; PCI, faster at 32 or 64 bits; and AGP, twice as
fast as PCI and designed to support video and 3-D graphics. Types of expansion
cards include the following: Graphics cards convert data into video
images to display on a monitor. Sound cards transmit digital sounds;
this includes music for video games created by wavetable synthesis,
digitized sound samples taken from recordings of actual instruments. Modem
cards are modems installed inside the computer. Network interface cards
allow data transmission over a cable network. The PC card is used principally
to expand the capabilities of laptops.
- Secondary Storage. Secondary storage hardware -- devices that permanently
hold data and programs -- include floppy disks, hard disks, optical disks,
magnetic tape, and smart cards. Online secondary storage is also possible.
Floppy disks are removable flat pieces of mylar plastic in 3.5-inch
plastic cases. Floppy disks have a write-protect notch, which can prevent
accidentally recording over on a disk. Data is recorded in concentric circles
called tracks; each track is divided into sectors, invisible
wedge-shaped sections used for storage reference purposes. In the disk drive,
the read-write head transfers data between the computer and the disk.
Besides 3.5-inch floppy disks, which hold 1.44 megabytes, other forms of removable
disks are floppy-disk cartridges, or higher-capacity removable disks
-- Zip disks, SuperDisks, and HiFD disks. Zip disks are special disks
with a capacity of 100 or 250 megabytes. SuperDisks have a capacity
of 120 megabytes, and a SuperDisk drive can also read 1.44-megabyte floppies.
HiFD disks have a capacity of 200 megabytes; the disk drive can also
read 1.44-megabyte floppies. Hard disks are thin but rigid metal platters covered with a substance
that allows data to be held in the form of magnetized spots. Disks are sealed
in a hard-disk-drive unit, which can be quite sensitive, susceptible to a
head crash, when the surface of the disk touches particles or the read/write
head, resulting in loss of data on the disk. Hard disks may be nonremovable
or removable. (1) A nonremovable hard disk is housed in the microcomputer
system unit and stores most programs and data. Ads for hard disks may specify
the hard-disk controller, a circuit board that positions the disk and
read/write heads. Popular hard-disk controllers are Ultra ATA (also
known as EIDE), which allows fast data transfer and high storage capacity,
and SCSI, which supports several disk drives as well as other peripheral devices.
(2) A removable hard disk (Iomega's Jaz, SyQuest's SparQ) consists
of one or two platters enclosed with read/write heads in a hard plastic case,
which is inserted into a microcomputer's cartridge drive. Large computer systems also have three types of secondary-storage devices:
(1) 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. (2)
Fixed-disk drives are high-speed, high-capacity disk drives that are
sealed in their own cabinets. (3) 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. Optical disks are removable disks on which data is written and read
through use of laser beams. Types of optical disks are CD-ROM, CD-R, CD-RW,
DVD-ROM, DVD-R, DVD-RW, and DVD-RAM. CD-ROM is a read-only disk that
holds prerecorded text, graphics, and sound. CD-R disks can be written
to once but can be read many times. CD-RW disks can be written to and
erased so the disk can be reused several times. DVD-ROM is a high-capacity
CD, storing up to 17 gigabytes. DVD-R disks allow one-time recording
by consumers. DVD-RW (for rewritable) and DVD-RAM (for random
access memory) can be recorded on and erased more than once. 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. Magnetic tape is thin plastic tape coated with a substance that can
be magnetized, with data represented by magnetized (1s) or unmagnetized (0s)
spots. Large computers tend to use magnetic-tape reels, small computers tend
to use tape cartridges, resembling audio cassettes. A smart card,
such as a telephone debit card, contains a microprocessor and memory chip.
An optical card is a laser-recordable, wallet-type card used with an
optical card reader. A final type of storage is online secondary storage,
in which secure online services provide backup storage.
- Future Developments in Processing & Storage. On the far horizon
in processing are technologies using nanotechnology, optical computing, DNA
computing, quantum computing, and molecular and dot computers. As for secondary
storage, one noteworthy development is that of higher-density disks,
such as a hard drive capable of holding 56 gigabytes per square inch. In the
future we may also see innovations in molecular electronics, storage
at the subatomic level, as in the use of holograms, microscopic magnets one
molecule in size, subatomic lines, and even bacteria. We may also see online
"storewidth," combining storage and bandwidth.
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2002 McGraw-Hill Higher Education