Information Technology Reference
In-Depth Information
SUMMARY
Principle
Computer hardware must be carefully selected to
meet the evolving needs of the organization and its
supporting information systems.
has greater capacity than memory. The primary characteris-
tics of secondary storage media and devices include access
method, capacity, portability, and cost. Storage media
can implement either sequential access or direct access.
Common forms of secondary storage include magnetic
tape, magnetic disk, virtual tape, optical disc, digital video
disc (DVD), and holographic versatile disc (HVD).
Redundant array of independent/inexpensive disks (RAID)
is a method of storing data that generates extra bits of data
from existing data, allowing the system to more easily recover
data in the event of a hardware failure.
Network-attached storage (NAS) and storage area net-
works (SAN) are alternative forms of data storage that enable
an organization to share data resources among a much larger
number of computers and users for improved storage
efficiency and greater cost-effectiveness.
The overall trend in secondary storage is toward direct-
access methods, higher capacity, increased portability, and
automated storage management. Interest in renting space on
massive storage devices is increasing.
Input and output devices allow users to provide data and
instructions to the computer for processing and allow sub-
sequent storage and output. These devices are part of a user
interface through which human beings interact with com-
puter systems.
Data is placed in a computer system in a two-stage
process: Data entry converts human-readable data into
machine-readable form; data input then transfers it to the
computer. Common input devices include a keyboard, a
mouse, speech recognition, digital cameras, terminals, scan-
ning devices, optical data readers, magnetic ink character
recognition devices, magnetic stripe cards, point-of-sale
devices, automated teller machines, pen input devices, touch-
sensitive screens, bar-code scanners, and Radio Frequency
Identification tags.
Display monitor quality is determined by size, color, and
resolution. Liquid crystal display and organic light-emitting
diode technology is enabling improvements in the resolution
and size of computer monitors. Other output devices include
printers, plotters, and digital audio players. E-books and
multiple-function printers are common forms of special-
purpose input/output devices.
Computer systems are generally divided into two cate-
gories: single user and multiple users. Single-user systems
include handheld, ultra laptop, portable, thin client, desktop,
and workstation computers.
Multiuser systems include servers, blade servers, main-
frames, and supercomputers.
Computer hardware should be selected to meet specific user
and business requirements. These requirements can evolve
and change over time.
The central processing unit (CPU) and memory cooperate
to execute data processing. The CPU has three main
components: the arithmetic/logic unit (ALU), the control unit,
and the register areas. Instructions are executed in a two-
phase process called a machine cycle that includes the
instruction phase and the execution phase.
Computer system processing speed is affected by clock
speed, which is measured in gigahertz (GHz). As the clock
speed of the CPU increases, heat is generated that can
corrupt the data and instructions the computer is trying to
process. Bigger heat sinks, fans, and other components are
required to eliminate the excess heat. This excess heat can
also raise safety issues.
Primary storage, or memory, provides working storage for
program instructions and data to be processed and provides
them to the CPU. Storage capacity is measured in bytes.
A common form of memory is random access memory
(RAM). RAM is volatile; loss of power to the computer erases
its contents. RAM comes in many different varieties including
dynamic RAM (DRAM), synchronous DRAM (SDRAM), Double
Data Rate SDRAM, and DDR2 SDRAM.
Read-only memory (ROM) is nonvolatile and contains per-
manent program instructions for execution by the CPU. Other
nonvolatile memory types include programmable read-only
memory (PROM), erasable programmable read-only memory
(EPROM), electrically erasable PROM, and flash memory.
Cache memory is a type of high-speed memory that CPUs
can access more rapidly than RAM.
A multicore microprocessor is one that combines two
or more independent processors into a single computer so
they can share the workload. Intel and AMD have introduced
quad-core processors that are effective in working on prob-
lems involving large databases and multimedia.
Parallel computing is the simultaneous execution of the
same task on multiple processors to obtain results faster.
Massively parallel processing involves linking many proces-
sors to work together to solve complex problems.
Grid computing is the use of a collection of computers,
often owned by multiple individuals or organizations, to work
in a coordinated manner to solve a common problem.
Computer systems can store larger amounts of data and
instructions in secondary storage, which is less volatile and
