Microprocessor Performance Factors

 

A microprocessor’s performance is affected by several factors, including clock speed, word size, cache size, instruction set, and processing techniques.

The microprocessor clock is a timing device that sets the pace for executing instructions. The speed of a microprocessor is usually specified in megahertz (MHz) gigahertz. A cycle is the smallest unit of time in a microprocessor’s universe. Every action a processor performsis measured by these cycles. The clock speed is not equal to the number of instructions a processor can execute in one second. In many computers, some instructions occur within one cycle, but other instructions might requiremultiple cycles. Some processors can execute several instructions in a single clock cycle.

Word size refers to the number of bits that a microprocessor can manipulate at one time. Word size is based on the size of registers in the ALU and the capacity of circuits that lead to those registers. A processor with a 32-bit word size, for example, has 32-bit registers, processes 32 bits at a time, and is referred to as a “32-bit processor”. Processors with a larger word size can process more data during each processor cycle that leads to increased computer performance.

Cache or “RAM cache” or “cache memory” is special high-speed memory that allows a microprocessor to access data more rapidly than from memory located elsewhere on the system board. Cache capacity is usually measured in kilobytes.

As chip designers developed various instruction sets for microprocessors, they tendedto add increasingly complex instructions, each requiring several clock cycles for execution. A microprocessor with such an instruction set uses CISC (complex instruction set computer) technology. A microprocessor with a limited set of simple instructions uses RISC (reduced instruction set computer) technology. A RISC processor performs most instructions faster than a CISC processor. It might, however, require more of these simple instructions to complete a task than a CISC processor requires for the same task. Most processors in today’s personal computer use CISC technology.

Some processors execute instruction “serially” – that is, one instruction at a time. With serial processing, the processor must complete all steps in the instruction cycle before it begins to execute the next instruction. However, using a technology called pipelining, a processor can begin executing an instruction before it completes the previous instruction. Many of today’s microprocessors also perform parallel processing, in which multiple instructions are executed at the same time. Pipelining and parallel processing enhance processorperformance.

Some computers have a single chip containingthe circuitry for two microprocessors. A dual core processor is faster than one with a single core.

Various testing laboratories run a series of tests to gauge the overall speed of a microprocessor. The results of these tests – called benchmarks – can then be comparedto the results for other microprocessors.

Random Access Memory

RAM (random access memory) is a temporary holding area for data, application program instructions, and the operating system. RAM is usually several chips or small circuit boards that plug into the system board within the computer’s system unit. RAM is the “waiting room” for the computer’s processor. It holds raw data waiting to be processed as well as the program instructions for processing that data.

RAM also holds the results of processing until they can be stored more permanently on disk or tape, it also holds data and application software instructions, operating system instructions that control the basic functions of a computer system. These instructions are loaded into RAM every time you start your computer, and they remain there until you turn off your computer.

People sometimes tend to confuse RAM and hard-disk storage, maybe because both components hold data, because they typically are “hidden” inside the system unit, or because they can both be measured in gigabytes. To differentiate between RAM and hard-disk storage, remember that RAM holdsdata in circuitry that’s directly connected to the system board, whereas hard-disk storage places data on magnetic media. RAM is temporary storage; hard-disk storage is more permanent. Besides, RAM usually has less storage capacity than hard-disk storage.

In RAM, microscopic electronic parts, called capacitors hold the bits that represent data. You can visualize the capacitors as microscopic lights that can be turned on and off. A charged capacitor is “turned on” and represents a”1” bit. A discharged capacitor is “turned off” and represents a “0” bit. Each bank of capacitors holds eight bits – one byte of data. A RAM address on each bank helps the computer locate data as needed, for processing.

Each RAM location has an address and uses eight capacitors to hold the eight bits that represent a byte. See Figure 1:

 

 

■		■	■	■	■	■			The two charged capacitors at the RAM address represent the letter “A”
■		■	■	■	■		■	A different sequence of charged capacitors represents the letter “B”
■		■	■	■	■			Another sequence of charged capacitors represents the letter “C”

 

Fig. 1: The way RAM represents different characters

 

In some respects, RAM is similar to a chalkboard. You can use a chalkboard to write mathematical formulas, erase them, and then write an outline for a report. RAM contents can be changed just by changing the charge of the capacitors.Unlike disk storage, most RAM is volatile, which means it requires electrical power to hold data. If the computer is turned off or the power goes out, all data stored in RAM instantly and permanently disappears.

Today’s personal computer operating systems are quite adept at allocation RAM space to multiple programs. If a program exceeds its allocated space, the operating system uses an area of the hard disk, called virtual memory, to store parts of programs or data files until they are needed. By selectively exchanging the data in RAM with the data in virtual memory, your computer effectively gains almost unlimited memory capacity.

RAM components vary in speed, technology, and configuration. RAM speed is often expressed in nanoseconds or megahertz. One nanosecond (ns) is 1 billionth of a second. RAM speed can also be expressed in MHz (millions of cycles per second). Most of today’s personal computers use SDRAM (synchronous dynamic RAM), fast and relatively inexpensive, it is typically available on a small circuit board called a DIMM (dual inline memory module) or RDRAM (Rambus dynamic RAM), first developed for a game system and then adapted for use in personal computers.

Read-Only Memory

ROM (read-only memory) is a type of memory circuitry that holds the computer’s startup routine. Whereas RAM is temporary and volatile, ROM is permanent and non-volatile. ROM circuitryholds “hard-wired” instructions that are a permanent part of the circuitry and remain in place even when the computer power is turned off.

When you turn on your computer, the microprocessor receives electrical power and is ready to begin executing instructions. As a result of the power being off, however, RAM is empty and doesn’t containany instructions for the microprocessor to execute. Now ROM plays its part. ROM containsa small set of instruction called the ROM BIOS (basic input/output system).These instructions tell the computer how to access the hard disk, find the operating system, and load it into RAM. After the operating system is loaded, the computer can understand your input, display output, run software, and access your data.

CMOS Memory

 

To operate correctly, a computer must have some basic information about storage, memory, and display configurations. The information is held in CMOS (pronounced “SEE moss”), a type of chip that requires very little power to holddata. It can be powered by a small battery that is integrated into the system board and automatically recharges while your computer power is on. The battery trickles power to the CMOS chip so that it can retain vital data about your computer system configuration even when your computer is turned off. When you change the configuration of your computer system, the data in CMOS must be updated.

The more data and programs that can fit into RAM, the less time your computer will spend moving data to and from virtual memory.

 

Comprehension check. Find the paragraph where the following ideas are found in the text.

1. It is the most significant component of the computer.

2. It executes logical operations, as well as arithmetic operations.

3. With this type of processing the processor performs one instruction at a time.

4. The results of the tests must match the results for model microprocessors.

5. If the allotted space is surpassed, the operating system employs an area of the hard disk.

6. The chip can hold the vital data about the configuration of your computer even when there is no energy supply.

Vocabulary practice

1. In the text, find the opposites to the given words.

 

fall short of reduce fail lose

 

2. Fill in the blanks choosing from the variants given.

 

1. CMOS memory is a type of chip that requires very little power to … data.

a) affect b) compare c) hold d) execute

2. As a result of the power being off RAM does not … any instructions for the microprocessor to execute.

a) contain b) allocate c) develop d) provide

3. The ALU uses registers to hold data as the microprocessor …arithmetic and logical operations.

a) gains b) compares c) performs d) exchanges

4. When the microprocessor receives electrical power, it is ready to begin … instructions.

a) executing b) exchanging c) allocating d) holding

5. Microprocessor instruction sets can be classified as … or ….

a) RAM or ROM b) CISC or RISC c) ROM BIOS d) CMOS memory

6. The instructions for loading the operating system into RAM when a computer is first turned on are stored in …memory.

a) RAM b) CMOS c) RISC d) ROM

7. A microprocessor (sometimes simplyreferred to as a “processor”) is an integrated circuit … to process instructions.

a) affected b) performed c) held d) designed

 

3. Make three-word expressions connected with computing combining words from three lists: A, B and C. Then fill in the gaps in the following sentences.

 

A: random B: system C: processor

read-only access configuration

computer core circuitry

dual memory memory

 

1. A … is faster than one with a single core.

2. The battery trickles power to the CMOS chip so that it can retain vital data about your ….

3. … holds the results of processing until they can be stored more permanently on disk or tape.

4. … holds “hard-wired” instructions that are a permanent part of the circuitry and remain in place even when the computer power is turned off.

4. Fill in the gaps in the text.

 

The microprocessor and memory are two of the most important components in a computer. The microprocessor is an integrated circuit, which is ___ to process data based on a set of instructions. The microprocessor’s ALU ___ arithmetic and logical operations. The control unit fetches each instruction, ___ it, loads data into the ALU registers, and directs all the processing activities within the microprocessor. Microprocessor performance is measured in ___ – the number of cycles per second, or clock rate. Other factors ___ overall processing speed include word size cache size, instruction set complexity, and ___.

Speaking. Discuss the following questions.

 

1. What exactly is a microprocessor? How does it work?

2. Where does the microprocessor get its instructions?

3. What impact does word size have on performance?

4. How does the cache size affect performance?

5. How does the instruction set affect performance?

6. What is the difference between serial processing and parallel processing?

7. How is it possible to compare microprocessor performance?

8. How does RAM differ from hard-disk storage?

9. If a computer has RAM, why does it need ROM?

10. Where does a computer store its basic hardware settings?

Text C

Pre-reading. Match the meaning of the following English words with their Russian equivalents.

1. storage	a) жесткий диск
2. medium	b) резервирование; резервная копия
3. read-write head	c) темное, неотражающее пятно на поверхности CD-ROM
4. pit	d)отражающее пятно на поверхности CD-ROM
5. solid state storage	e)универсальная головка считывания – записи
6. land	f)авария (плавающих) головок
7. platter	g) контроллер, устройство управления
8. head crash	h) запоминающее устройство на монолитном носителе
9. backup	i) память, запоминающее устройство
10. controller	j) носитель; средство

Reading. Read the text and try to guess the meaning of the words in bold font. Check your variants in the dictionary.

STORAGE DEVICES

Storage Basics

 

A data storage system has two main components: a storage medium and a storage device. A storage medium (storage media is the plural) is the disk, tape, CD, DVD, or other substances that contains data. A storage device is the mechanical apparatus that records and retrieves data from a storage medium. Storage devices include hard disk drives, tape drives, CD drives, and DVD drives. The term “storage technology” refers to a storage device and the media it uses.

You can think of your computer’s storage devices as having a direct pipeline to RAM. Data is copied from a storage device into RAM, where it waits to be processed. After data is processed, it is held temporarily in RAM, but it is usually copied to a storage medium for more permanent safekeeping. A computer works with data that has been coded into bits that can be represented by 1s and 0s. Obviously, the data is not literally written as “1” or “0”. Instead, the 1s and 0s must be transformed into changes in the surface of a storage medium. Exactly how this transformation happens depends on the storage technology. Three types of storage technologies are used for personal computer: magnetic, optical, and solid state.

Hard disk, floppy disk, and tape storage technologies can be classified as magnetic storage, which stores data by magnetizing microscopic particles on the disk or tape surface. Before data is stored, particles on the surface of the disk are scattered in random patterns. The disk drive’s read-write head magnetizes the particles, and orients them in a positive (north) or negative (south) direction to represent 0 and 1 bits. Data stored magnetically can be easily changed or deleted. This feature of magnetic storageprovides lots of flexibility for editing data and reusing areas of a storage medium containing unneeded data. Data stored on magnetic media such as floppy disks can be altered by magnetic fields, dust, mould, smoke particles, heat, and mechanical problems with a storage device. Magnetic media gradually lose their magnetic charge, resulting in lost data. Some experts estimate that the reliable life span of data stored on magnetic media is about three years. They recommend that you refresh your data every two years by recopying it.

CD and DVD storage technologies can be classified as optical storage, which stores data as microscopic light and dark spots on the disksurface. The dark spots are called pits. The lighter, non-pitted surface areas of the disk are called lands. Optical storage gets its name because data is read using a laser light. The transition between pitsand lands is interpreted as the 1s and 0s that represent data. An optical storage device uses a low-power laser light to read the data stored on an optical disk. The surfaceof an optical disk is coated with clear plastic, making the disk quite durable and less susceptible to environmental damage than data recorded on magnetic media. An optical disk, such as a CD, is not susceptible to humidity, fingerprints, dust, magnets, or spilled soft drinks, and its useful life is estimated at more than 30 years.

A variety of compact storage cards can be classified as solid state storage, which stores data in a non-volatile, reusable, low-power chip. The chip’s circuitry is arranged as a grid, and each cell in the grid contains two transistors that act as gates. When the gates are open, current can flow and the cell has a value that represents a “1” bit. When the gates are closed, the cell has a value that represents a “0” bit. Very little power is required to open or close the gates, which makes solid state storage ideal for battery-operated devices. Once the data is stored, it is non-volatile – the chip retains the data without the need for an external power source.

Floppy Disk Technology

 

Floppy disks are classified as magnetic storage because data is stored by magnetizing microscopic particleson the disk surface. A floppy disk is a round piece of flexible mylar plastic covered with a thin layer of magnetic oxide and sealed inside a protective casing.

Hard Disk Technology

 

Hard disk technology is the preferred type of main storage for most computer systems. A hard disk is one or more platters and their associated read-write heads. A hard disk platter is a flat, rigid disk made of aluminum or glass and coated with magnetic iron oxide particles. Hard disk platters are sealed inside the drive case or cartridge to screen out dust and other contaminants. The sealed case contains disk platters and read-write heads. Each platter has a read-write head that hovers over the surface to read data. The drive spindle supports one or more hard disk platters. Both sides of the platter are used for data storage. More platters mean more data storage capacity. Hard disk platters rotate as a unit on the spindle to position read-write heads over specific data. The platters spin continuously, making thousands of rotations per minute. Each data storage surface has its own read-write head, which moves in and out from the center of the disk to locate data. The head hovers only a few microinches above the disk surface, so the magnetic field is more compact than on a floppy disk. As a result, more data is packed into a smaller area on a hard disk platter. The density of particles on the disk surface provides hard disks with capacities far greater than floppy disks. Also, the access time for a hard disk is significantly faster than for a floppy disk.

A hard disk drive stores data at the same locations on all platters before moving the read-write heads to the next location. A vertical stack of storage locations is called a “cylinder” – the basic storage bin for a hard disk drive. A hard drive mechanism includes a circuit board called a controller that positions the disk and read-write heads to locate data. The storage technology used on many PCs transfers data from a disk, through the controller, to the processor, and finally to RAM before it is actually processed.

Hard disks are not as durable as many other storage technologies. The read-write heads in a hard disk hover a microscopic distance above the disk surface. If a read-write head runs into a dust particle or some other contaminant on the disk, it might cause a head crash, which damages some of the data on the disk. To help prevent contaminants from contacting the platters and causing head crashes, a hard disk is sealed in its case. A head crash can also be triggered by jarring the hard disk while it is in use. Although hard disks have become considerably more rugged in recent years, you should still handle and transport them with care. You should make a backup copy of the data stored on your hard disk in case of a head crash.

Tape Storage

 

A head crash can easily destroy hard disk data. A tape backup is a copy of the data on a hard disk, which is stored on magnetic tape and used to restore lost data. A tape backup device can simplify the task of reconstructing lost data. A backup tape can hold the entire contents of a hard disk.

CD and DVD Technology

 

Today, most computers are equipped with some type of optical drive – a CD drive or a DVD drive. The underlying technology for CD and DVD drives is similar, but storage capacities differ. CD and DVD drives contain a spindle that rotatesthe disk over a laser lens. The laser directs a beam of light toward the underside of the disk. Dark “pits” and light “lands” on the disk surface reflect the light differently. As the lens reads the disk, these differences are translated into the 0s and 1s that represent data. Optical drives use several technologies to write data on CD and DVD disks: Recordable technology (R) uses a laser to change the color in a dye layer sandwiched beneath the clear plastic disk surface. The laser creates dark spots in the dye that are read as pits. The change in the dye is permanent, so the data cannot be changed once it has been recorded. Rewritable technology (RW) uses “phase change” technology to alter a crystal structure on the disk surface. Altering the crystal structure creates patterns of light and dark spots similar to the pits and lands on a CD. The crystal structure can be changed from light to dark and back again many times, making it possible to record and modify data much like on a hard disk. Most CD drives can read CD-ROM, CD-R, and CD-RW disks, but cannot read DVDs. Most DVD drives can read CD and DVD formats.

Solid State Storage

Solid state storage is portable, provides fast access to data, and uses very little power, so it is an ideal solution for storing data on mobile devices and transporting data from one device to another. It is widely used in portable consumer devices, such as digital cameras, MP3 music players, notebook computers, PDAs, and cell phones. A USB flash drive is a portable storage device. It is durable and requires no card reader, making it easily transportable from one computer to another. You can open, edit, delete, and run files stored on a USB flash drive just as though those files were stored on your computer’s hard disk.

Comprehension check. Choose the ending for each sentence from the two versions given.

1. A storage device is the mechanical apparatus	a) that hovers over thesurface to read data.
b) that records andretrieves data from a storage medium.
2. After data is processed, it is held temporarily in RAM,	a) you should still handle andtransport them with care.
b) but it is usually copied to a storage medium for more permanent safekeeping.
3. Before data is stored,	a)particles on thesurface of the disk are scattered in random patterns.
b) dark spots in the dye that are read as pits.
4. Hard disk, floppy disk, and tape storage technologies can be classified as magnetic storage,	a) making it easily transportable from one computer to another.
b) which stores data by magnetizing microscopic particleson the disk or tape surface.
5. The surface of an optical disk is coated with clear plastic,	a) which damages some of the data on the disk.
b) making the disk less susceptible to environmental damage than data recorded on magnetic media.
6. An optical disk, such as a CD, is not susceptible to magnets, dust, humidity,	a) and transfers data from a disk to RAM before it is actually processed.
b) and its useful life is estimated at more than 30 years.

Vocabulary practice

1. Which word does not belong to the group?

a) transportable, optical, susceptible, particle;

b) gates, retrieves, provides, handles;

c) storage, medium, magnetic, device;

d) converted, changed, transformed, stored;

e) transport, process, estimate, access;

f) disk, tape, drive, DVD;

2. Fill in the missing words choosing from the variants given.

1. A magnetic storage device uses a read-write head to magnetize … that represent data.

a) lens b) particles c) contents d) platters

2. Data on an optical storage medium, such as DVD, is stored as … and lands.

a)lands b) bits c) bytes d) pits

3. … time is the average time it takes a computer to locate data on a storage medium and read it.

a) revolution b) transporting c) valuable d) access

4. The laser creates dark spots in the dye layer that are read as ….

a) areas b) plates c) pits d) particles

5. Higher disk density provides increased storage ….

a) transformation b) capacity c) flexibility d) data

6. Hard disks are … to head crashes, so it is important to make backup copies.

a) susceptible b) optical c) retrievable d) transportable

3. Transform the following sentences without any change in meaning. Use the prompts as they are given (words in brackets, parts of sentences).

1. A storage device is the mechanical apparatus for recording and restoring data from a storage medium (retrieve).

The user ….

2. Hard disks should be operated and moved with care (handle, transport).

One ….

3. The translation of the differences between pits and lands into binary numbers is provided by the lens (translated).

The … between pits and lands into binary numbers ….

4. Revolving hard disk platters on the spindle allows the disk drive to position read-write heads over specific data (rotated).

To position read-write heads over specific data ….

5. High capacities of hard disk are available due to the high density of particles on the disk surface. (provides)

High density of particles ….

6. You can gauge hard disk drive speed in revolution per minute (pm). (to measure)

Revolution per minute ….

7. On many computers before data is actually processed, it is moved from a disk to RAM using the storage technology (processed, transfer).

Before data is actually …, ….

4. Fill in the gaps with appropriate words.

Personal computers use a variety of ___ technologies, including hard drives, CDs, DVDs, and flash drives. Each storage device essentially has a direct pipeline to a computer’s ___ so that data and instructions can move from a more permanent storage area to a temporary holding area and vice versa. Magnetic storage technology stores data by magnetizing microscopic ___ on the surface of a disk or tape. Optical storage technologies store data as a series of ___ and lands on the surface of a CD or DVD. ­­­­­­­___ ___ storage technology stores data by activating electrons in a microscopic grid of circuitry. A standard 3.5" floppy disk for a PC stores ___ MB of data. A hard disk provides multiple ___ for data storage. Optical storage technologies, such as CD- and DVD- ___, provide good data storage capacity.

 

Speaking. Discuss the following questions.

1. What are the basic components of a data storage system?

2. How does a storage system interact with other computer components?

3. How does magnetic storage work?

4. How does optical storage work?

5. What are the advantages of solid state storage?

6. What is floppy disk technology?

7. How does a hard disk work?

8. What’s the downside of hard disk storage?

9. What’s the purpose of a tape drive?

10. What is the difference between CD and DVD technology?

Text D

Pre-reading. Match the meaning of the following English words with their Russian equivalents.

1. CRT (cathode ray tube) display	a) жидкокристаллический дисплей
2. dot pitch	b) плата расширения
3. viewing angle	c) указательное устройство
4. width	d) шаровой указатель; шаровой манипулятор
5. expansion card	e) клавиатура
6. expansion slot	f) угол обзора
7. keyboard	g) частота регенерации; частота обновления
8. LCD (liquid crystal display)	h) кинескоп, электронно-лучевая трубка
9. pixel	i) шаг расположения точек
10. pointing device	j) пиксель, минимальный элемент изображения
11. refresh rate	k) ширина; горизонтальный размер
12. trackball	l) контактная площадка, трекпэд
13. trackpad	m) гнездо для платы
14. PnP	n) включай и работай

Reading. Read the text and try to guess the meaning of the words in bold font. Check your variants in the dictionary.

INPUT AND OUTPUT DEVICES

Basic Input Devices

 

Most computer systems include a keyboard and pointing device, such as a mouse, for basic data input. Additional input devices, such as scanners, digital cameras, and graphics tablets, are handy for working with graphical input. Microphones and electronic instruments provide input capabilities for sound and music. A keyboard allows the user to key in programs and data and to control the computer system. Letters, numbers, symbols and blank spaces are known as characters. Thedesign of most computer keyboards is based on the typewriter’s QWERTY layout (because these are the first six letters on the top left of the keyboard), which was engineered to keep the typewriter’s mechanical keys from jamming. In addition to the basic typing keypad, computer keyboards include a collection of function keys designedfor computer-specific tasks, a calculator-style numeric keypad, and an editing keypad with keys such as End, Home, and Page Up.

A pointing device allows you to manipulate an on-screen pointer and other screen-based graphical controls. The most popular pointing devices for personal computers include mice, trackballs, pointing sticks, trackpads, and joysticks. A standard desktop computer includes a mouse as its primary pointing device. A mouse includes one or more buttons that can be “clicked” to input command selections. To track its position, a computer mouse uses one of two technologies: mechanical or optical. A mechanical mouse reads its position based on the movement of a ball that rolls over a mouse pad placed on a desk. An optical mouse uses an onboard chip to track a light beam as it bounces off a surface, such as a desk, clipboard, or mouse pad. An optical mouse provides more precise tracking, greater durability, less maintenance, and more flexibility to use the mouse on a wide variety of surfaces without a mouse pad. A pointing stick, looks like the top of an eraser embedded in the keyboard of a notebook computer. A trackpad is a touch-sensitive surfaceon which you can slide your fingers to move the on-screen pointer. A trackball looks like a mechanical mouse turned upside down. A joystick looks like a small version of a car’s stick shift and is used mostly for playing games.

Display Devices

 

A computer display screen is usually classified as an output device because it typically shows the results of a processing task. Some screens, however, can be classified as both input and output device because they include touch-sensitive technology that accepts input. Display devices used for output offer three technology options: CRT, LCD, and plasma. Gun-like mechanisms in the CRT (cathode ray tube) spray beams of electrons toward the screen and activate individual dots of color that form an image. CRT display devices often simply called “monitors”, are bulky, however, and consume a fair amount of power. An LCD (liquid crystal display) produces an image by manipulating light within a layer of liquid crystal cells. Modern LCD technology is compact in size and lightweight, andprovides an easy-to-read display. The advantages of LCD monitors (or “flat panel displays”) include display clarity, low radiation emission, portability, and compactness. Plasma screen technology creates an on-screen image by illuminating miniature colored fluorescent light arrayed in a panel-like screen. The name “plasma” comes from the type of gas that fills fluorescent lights and gives them their luminescence. Like LCD screens, plasma screens are compact, lightweight, and more expensive than CRT monitors. They are rather energy consuming, too.

Image quality is a factor of screen size, dot pitch, width of viewing angle, refresh rate,resolution, and color depth. Screen size is the measurement in inches from one corner of the screen diagonally across to the opposite corner.The quality of a screen is often measured by the number of horizontal and vertical pixels used to create it. A pixel is a dot of color on a photo image or a point of light on a display screen. It can be in one of two modes: “ on” or “off”. A larger number of pixels per square inch means a higher res­olution, or clarity and sharpness of the image. The distance between one pixel on the screen and the next nearest pixel is known as dot pitch. Dot pitch (dp) is a measure of image clarity. A smaller dot pitch means a clearer image. Greater pixel den­sities and smaller dot pitches yield sharper images of higher resolution. A monitor’s viewing angle width indicates how far to the side you can still clearly see the screen image. A wide viewing angle indicates that you can view the screen from various positions without compromising image quality. CRT and plasma screens offer the widest viewing angles. A CRT’s refresh rate (also referred to as“vertical scan rate”) is the speed at which the screen is repainted. The faster the refresh rate, the less the screen flickers. Refresh rate is measured in cycles per second, or Hertz (Hz). The number of colors a monitor can display is referred to as color depth or “bit depth”. Most PC display devices have the capability to display millions of colors. The number of horizontal and vertical pixels that a device displays on a screen is referred to as its resolution. The resolution for many early PC displays was referred to as VGA (Video Graphics Array). Higher resolutions were later provided by SVGA (SuperVGA), XGA (eXtended Graphics Array), SXGA (Super XGA), and UXGA (Ultra XGA).

Printers

 

Printers are one of the most popular output devices, they usually use ink jet or laser technology. An ink jet printer has a nozzle-like print head that sprays ink onto paper to form characters and graphics. A laser printer uses the same technology as a photocopier to paint dots of light on a light-sensitive drum. Laser technology is more complex than ink jet technology, which accounts for the higher price of laser printers. A recurring cost of using a printer is the ink-jet or laser cartridge that must be replaced every few thousand pages of output.Printers differ in resolution, speed, duty cycle, operating costs, duplex capability, and memory. Printer resolution – the density of the gridwork of dots that create an image – is measured by the number of dots printed per linear inch, abbreviated as dpi, normally 900 dpi is enough. Printer speeds are measured either by pages per minute (ppm) or character per second (cps). A printer’s duty cycle determines how many pages a printer is able to process, usually measured per month (ppm). A printer with duplex capability can print on both sides of the paper, though it will slow down the print process. A computer sends data for a printout to the printer along with a set of instructions on how to print that data. Printer Control Language (PCL) is the most widely used language for communication between computers and printers, but PostScript is an alternative printer language that many publishing professionals prefer. The data that arrives at a printer along with its printer language instructions requires memory.