Chapter 3 - Hardware: Input, processing, and output devices
Chapter Hardware and Software
Information system professionals need to have a detailed understanding of capabilities of various hardware devices used in information system to make the right choice in designing information systems.
Computer hardware must be carefully selected to meet the evolving needs of the organization and its
supporting information systems.
The computer hardware industry and users are implementing green computing designs and products.
Principle:Assembling an effective, efficient computer system requires an understanding of its relationship to the information system and the organization. The computer system objectives are subordinate to, but supportive of the information system and the organization.
Principle:When selecting computer devices, you also must consider the current and future needs of the information system and the organization. Your choice of a particular computer system device should always allow for later improvements.
telecommunications, people and procedures, organised to input, process, and output data
Elements of the CPU:
1. ALU (arithmetic/logic unit): Performs calculations and makes logical comparisons.
2. Control unit: Sequentially accesses program instructions, decodes them, and coordinates the flow of data in and out of the ALU, registers, primary storage, and output devices.
3. Register: = Storage areas used to temporarily hold small units of instructions and data immediately
before, during, and after execution by the CPU.
Primary storage (main memory / memory) = part of the computer that holds program
instructions and data just before / after the registers. (Secondary storage is more permanent).
Hardware components in action
Phase 1: Instruction (I-time = the time it takes to perform phase 1)
Step 1: Fetch instruction (The control unit fetches the instruction from memory)
Step 2: Decode instruction (The instruction is interpreted)
Phase 2: Execution (E-time = the time it takes to complete execution)
Step 3: Execute the instruction (The ALU does what it is instructed to do)
Step 4: Store results (The results are stored in registers or memory)
Pipelining = executing multiple phases in a single machine cycle.
Processing and memory devices
Processing characteristics and functions
Processing speed - measured by the time it takes to complete a machine cycle & clock speed
Machine cycle time: Machine cycle times are measured in microseconds, nanoseconds and picoseconds. They can also be measured in MIPS (Millions of Instructions Per Second)
Clock speed: A series of electronic pulses, created by the CPU, that affect machine cycle time.
The control unit of the CPU controls the various stages of the machine cycle by following
internal instructions, called microcode.
Microcode is predefined, elementary circuits and logical operations that the processor
performs when it executes an instruction.
The control unit executes the microcode in accordance with the clock pulses.
The shorter the interval between pulses, the faster the execution of microcode instructions.
Clock speed is measured in MegaHertz (MHz) - Millions of cycles per second
A hertz is one cycle / pulse per second.
There is no direct relationship between clock speed (MHz) and processing speed (MIPS)
Wordlength and Bus Line Width
A factor affecting speed is wordlength of the CPU.
Wordlength is the number of bits the CPU can process at any one time.
Data is transferred from the CPU to other system components via bus lines.
Bus line is the physical wiring that connects the components.
Bus line width is the number of bits a bus line can transfer at any one time.
Bus line width should match CPU wordlength for optimal system performance.
The megahertz rating is not necessarily a good measure of the processor performance.
Intel have developed a benchmark for speed: iCOMP (Intel Comparative Microprocessor
Physical characteristics of the CPU
CPU speed is also limited by physical constraints.
CPUs are collections of digital circuits imprinted on silicon chips.
The speed at which current travels between points can be increased by either reducing the
distance between the points / reducing the resistance of the medium to the current.
Moore’s law: “The transistor densities on a chip will double every 18 months”.
Another substitute material for silicon chips is superconductive metal.
Superconductivity: In certain metals, current flows with minimal electrical resistance.
(Traditional silicon chips create some resistance that slows processing).
Optical processors = chips that use light waves, instead of current, to represent bits.
They can be 500 times faster than traditional electronic circuits.
Complex and Reduced Instruction Set Computing (CISC) & (RISC)
CISC = a chip design that places as many microcode instructions into the CPU as possible.
But most operations of a CPU involve only 20% of the available microcode instructions.
RISC involves reducing the number of microcode instructions to a set of common ones.
RISC chips are faster than CISC for processing activities that mainly use core instructions.
Most RISC chips use pipelining and they’re fast & cheap.
VLIW (Very Long Instruction Word) = a chip that reduces the number of instructions by
lengthening each one.
These are potentially even faster than RISC-based chips.
Memory characteristics and functions
Storage capacity is measured in bytes, with one byte equal to one character.
Kilobyte = one thousand
Megabyte = one million
Gigabyte = one billion
Terabyte = one trillion (each level is 1000 times larger!)
Types of memory
RAM (= main memory) (= volatile memory) chips lose their contents if the current is turned off.
EDO RAM (Extended data out) is faster than older types of RAM. (= MAINSTREAM RAM!!!!)
SDRAM (Synchronous Dynamic) - faster transfer speed between CPU and memory.
ROM (non-volatile memory) - contents are not lost if the power is removed.
PROM (Programmable) - first program data into the chip; thereafter it behaves like ROM.
PROM chips are used for storing instructions to popular video games.
Instructions can be programmed onto a PROM chip only once.
EPROM (Erasable Programmable) chips are used when instructions change, infrequently.
Cache memory = high-speed memory that processors can access quicker than main memory.
Frequently used data is stored in easily accessible cache memory.
Level 1 (L1) cache is in the processor.
Level 2 (L2) cache memory is optional and found on the motherboard.
Cacheable memory = the main memory that can move its information into cache memory.
= Simultaneous execution of 2 / more instructions at the same time.
Coprocessing executes instructions while the CPU works on another processing activity.
Coprocessors can be internal / external to the CPU and can have different clock speeds.
Each type of coprocessor performs a specific function.
Several processors are linked to operate at the same time.
A problem is divided into parts, and each part is solved by a separate processor.
= Permanent storage.
Secondary storage is slower than memory
Sequential access - data must be accessed in the order in which it is stored.
SADS = sequential access storage device
Direct access - data can be retrieved directly. (= faster)
DASD = direct access storage devices.
While disk drives can be operated as sequential storage devices, they most commonly use
direct access storage.
Portions of tape are magnetised to represent bits.
Slower access (sequential) but cheaper than disk storage.
Often used for backup.
Amount of data that can be stored is determined by the number of tracks, density, and the
block factor on the tape.
Block factor = the number of logical records per physical record (block).
Data is written to / read from blocks on magnetic tape.
At the end of each block there is an empty space, the IBG - InterBlock Gap.
Transfer rate = the number of characters per second that can be transferred.
Thin steel platters, with bits represented by magnetised areas. (E.g. Hard disks / diskettes)
Disk devices can be operated in a sequential mode, but most use direct access.
Hard disks have greater storage capacity and quicker access time than diskettes.
Data is stored as magnetised dots on the disk surface in concentric circles called tracks.
Sector = a subdivision of a track that holds a specific number of characters.
Cylinder = all tracks on a disk pack that are stacked vertically and have the same track no.
Speed of magnetic disks is expressed by: seek / head switching / rotation / data transfer time.
Redundant array of independent / inexpensive disks.
Extra bits of data are generated, creating a ‘reconstruction map’ so lost data can be rebuilt.
Striping evenly splits data across multiple disks.
Disk mirroring produces a backup disk for each disk. (= the simplest form of RAID)
Disk mirroring is expensive because you need to double the amount of storage capacity.
Other RAID methods are less expensive because they only partly duplicate the data.
RAID is needed if storage devices must be fault tolerant (= the ability to continue with no loss
of performance if a component fails)
RAID improves system performance and reliability.
Storage Area Network = technology that uses computer servers, distributed storage devices,
and networks to tie the storage system together.
= Rigid disks of plastic onto which data is recorded by lasers that burn pits in the disks.
An optical device uses a laser that measures reflected light caused by pits, to access data.
Each pit represents binary 1; each unpitted area (land) represents binary 0.
Advantage: Greater storage capacities than diskettes.
Disadvantage: Slower access times than diskettes.
CD-ROM - Read only (data can’t be modified)
CD-W - Writeable (data can be written once to a disk)
CD-RW -Rewritable (CDs can be written on and edited over)
= A hybrid between a magnetic & optical disk.
Like magnetic disks, MO disks can be read & written to.
Like diskettes, they are removable.
They are faster than diskettes, but not as fast as hard drives.
Their storage capacity can be more than 200MB (much greater than magnetic diskettes)
A laser beam changes the molecular configuration of a magnetic substrate on the disk,
creating visual spots, which are measured by another laser beam.
The presence or absence of a spot indicates a bit.
The disk can be erased by demagnetising the substrate, which removes the spots.
Can provide capacity of up to 17 GB. (135 minutes of digital video).
DVD players can read CD-ROMs, but not the other way round.
DVDs are thinner than CDs and their access speeds are faster.
= Credit card size devices that can be installed in an adapter / slot in many PCs / laptops.
They are less failure prone than hard disks, are portable, and easy to use.
= A silicon computer chip that, unlike RAM, is non-volatile (i.e. keeps its memory).
Flash memory chips are small and can be easily modified and reprogrammed.
Used in cell phones, handheld computers, digital cameras…
Advantages: Quick access, consumes less power, smaller in size.
Expandable storage devices use removable disk cartridges.
They can be internal / external and are ideal for backups.
More expensive than fixed hard disks, but combine hard disk storage capacity with portability.
They have become popular because they provide:
* More direct access methods
* Higher capacity
* Increased portability
Input and output devices
Characteristics and functionality
The nature of data
Human-readable data = data that can be understood by humans (instructions on paper…)
Machine-readable data = data that can be understood by computers (bar codes…)
Data can be both human & machine-readable (e.g. magnetic ink on bank cheques)
Data entry and input
Data entry = converting human-readable data into a machine-readable form.
Data input = transferring the machine-readable data into the system.
Source data automation
= Capturing & editing data at its source in a form that can be directly input to a computer.
Errors can be detected and corrected immediately.
Personal computer input devices
Keyboard & mouse.
Microphones & software record and convert human speech into digital signals.
Advantage: saves time.
Digital computer cameras
Pixel = a dot of colour on a photo image / a point of light on a display screen.
A terminal is connected to a complete computer system with a processor, memory…
Optical data readers
OMR (optical mark recognition) - for test scoring.
OCR (optical character recognition) - handwritten documents are converted into digital data.
Data printed with magnetic ink is readable by both people and computers.
Point-of-sale devices (POS)
= Terminals used in retail to enter sales info into the computer.
Pen input devices
By touching the screen with a pen input device, you can activate commands.
Pen input requires special hardware & software.
Handwriting recognition software can convert handwriting on the screen into text.
A light pen uses a light cell in its tip, which determines the pen’s location on the screen.
Bar code scanners
Display monitors (CRT)
Cathode Ray Tubes generate electron beams, which strike a phosphorescent compound on
the inside of the screen, which lights up pixels.
Dot pitch = the distance between one pixel and the next.
Greater pixel densities and smaller dot pitches yield sharper images of higher resolution.
A monitor’s ability to display colour is a function of:
the quality of the monitor
the amount of RAM in the computer
the monitor’s graphics adapter card
CGA (colour graphics adapter) was one of the first technologies to display colour on screens.
SVGA (super video graphics array) displays are standard, providing vivid colours.
Liquid crystals placed between two polarisers form characters on a backlit screen.
Printers and plotters
Speed is measured in ppm (pages per minute)
The quality depends on the number of dots per inch (dpi).
Plotters are used for general design work, like blueprints, drawings of buildings…
Computer output microfilm (COM) devices
Newspapers & journals typically place past publications on microfilm.
MP3 = (Motion Picture Experts Group Audio Layer 3) = a popular music format for the Internet
The MP3 standard allows for the music to be compressed, so it takes less time to download.
Special-purpose input and output devices
Multifunction device = one that can combine a printer, fax machine, scanner, copy machine…
They are cheaper than buying the devices separately and take up less room.
Types, standards, selecting, and upgrading
Network PC workstation midrange mainframe supercomputer
Computer system types
Personal computers = Microcomputers
Desktop, laptop, notebook, palmtop, embedded computers,
network computers (= cheaper version of the PC with less storage & power),
workstations (= between high-end PCs and low-end midrange computers in terms of cost &
processing power. They are used to support engineering & technical users with CAD etc…),
Web appliances (= devices that connect to the Internet, like a cell phone)
Midrange computers = Minicomputers
= Larger computers that can accommodate several users at the same time.
They have excellent processing & decision-support capabilities.
= Large, powerful computers shared by hundreds of concurrent users connected via terminals
They need a room with special Heating, Venting, and Air-Conditioning (HVAC) equipment.
They require specially trained individuals (system engineers) to care for them.
Computer downsizing = migration of information processing onto smaller computers.
Mainframes nowadays run jobs & store files too large for other computers.
Data warehouses = these large stores of data (like backups of databases…)
CMOS (complimentary metal oxide semiconductor) = a technology that uses special
semiconductor material to achieve low-power dissipation.
CMOS = a memory chip used to store configuration info about the computer.
Mainframes have become smaller, faster, cheaper systems as a result of CMOS processors.
They were originally used by the government, but are now used for commercial purposes.
Used for scientific and military research, and by universities / companies involved in research.
Equipped with microphones, speakers, cameras… and produce video, audio, text…
CD-ROM = a popular delivery medium for multimedia because of its large storage capacity.
Sound is converted to a digital recording for storage, and back to sound when played.
Digital Signal Processor (DSP) chips improve the analogue-to-digital-to-analogue conversion.
Video is the most difficult element to display because of the large amount of storage required.
Video compression reduces the number of bits required by using mathematical formulas.
You can add a video board to your PC for higher-quality video.
E.g. MIDI, Plug ‘n Play…
* Diminish the cost of integration
* Help developers determine which devices will be compatible with the rest of the system
* Provide increased options / flexibility
* Make upgrading a system less complex
Selecting and upgrading computer systems
Computer system architecture = the structure / configuration of the hardware components.
Computers may need to be upgraded to support new activities and a changing environment.