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INPUT OUTPUT DEVICES
The computer has processed your data, you often need to produce output of the results. This output could be a display on the computer screen, hardcopy on printed pages, or even the audio playback of music you composed on the computer.The terms “input” and “output” are used both as verbs to describe the process of entering or displaying the data, and as nouns referring to the data itself entered into or displayed by the computer. Below we discuss the variety of peripheral devices used for computer input and output. Input Devices
Keyboard
Input Devices Keyboard Mouse Touch pad Track Ball Other Output Devices CRT Monitor Flat Panel Display Ink Jet Printer Laster Printer The computer keyboard is used to enter text information into the computer, as when you type the contents of a report. The keyboard can also be used to type commands directing the computer to perform certain actions. Commands are typically chosen from an on-screen menu using a mouse, but there are often keyboard shortcuts for giving these same commands. In addition to the keys of the main keyboard (used for typing text), keyboards usually also have a numeric keypad (for entering numerical data efficiently), a bank of editing keys (used in text editing operations), and a row of function keys along the top (to easily invoke certain program functions). Laptop computers, which don’t have room for large keyboards, often include a “fn” key so that other keys can perform double duty (such as having a numeric keypad function embedded within the main keyboard keys). Improper use or positioning of a keyboard can lead to repetitive-stress injuries. Some ergonomic keyboards are designed with angled arrangements of keys and with built-in wrist rests that can minimize your risk of RSIs. Most keyboards attach to the PC via a PS/2 connector or USB port (newer). Older Macintosh computers used an ABD connector, but for
several years now all Mac keyboards have connected using USB.
Pointing Devices
The graphical user interfaces (GUIs) in use today require some kind of device for positioning the on-screen cursor. Typical pointing devices are: mouse, trackball, touch pad, trackpoint, graphics tablet, joystick, and touch screen.Pointing devices, such as a mouse, connected to the PC via a serial ports (old), PS/2 mouse port (newer), or USB port (newest). Older Macs used ADB to connect their mice, but all recent Macs use USB (usually to a USB port right on the USB keyboard).
Mouse
The mouse pointing device sits on your work surface and is moved with your hand. In older mice, a ball in the bottom of the mouse rolls on the surface as you move the mouse, and internal rollers sense the ball movement and transmit the information to the computer via the cord of the mouse.The newer optical mouse does not use a rolling ball, but instead uses a light and a small optical sensor to detect the motion of the mouse by tracking a tiny image of the desk surface. Optical mice avoid the problem of a dirty mouse ball, which causes regular mice to roll unsmoothly if the mouse ball and internal rollers are not cleaned frequently.A cordless or wireless mouse communicates with the computer via radio waves (often using BlueTooth hardware and protocol) so that a cord is not needed (but such mice need internal batteries). A mouse also includes one or more buttons (and possibly a scroll wheel) to allow users to interact with the GUI. The traditional PC mouse has two buttons, while the traditional Macintosh mouse has one button. On either type of computer you can also use mice with three or more buttons and a small scroll wheel (which can also usually be clicked like a button).
Touch pad
Two-button mouse with scroll wheel Wireless Macintosh mouse
Touch screen
Some computers, especially small hand-held PDAs, have touch sensitive display screens. The user can make choices and press button images on the screen. You often use a stylus, which you hold like a pen, to “write” on the surface of a small touch screen.
Graphics tablet
A graphics tablet consists of an electronic writing area and a special “pen” that works with it. Graphics tablets allows artists to create graphical images with motions and actions similar to using more traditional drawing tools. The pen of the graphics tablet is pressure sensitive, so pressing harder or softer can result in brush strokes of different width (in an appropriate graphics program).
Scanners
A scanner is a device that images a printed page or graphic by digitizing it, producing an image made of tiny pixels of different brightness and color values which are represented numerically and sent to the computer. Scanners scan graphics, but they can also scan pages of text which are then run through OCR (Optical Character Recognition) software that identifies the individual letter shapes and creates a text file of the page's contents.
Microphone
A microphone can be attached to a computer to record sound (usually through a sound card input or circuitry built into the motherboard). The sound is digitized—turned into numbers that represent the original analog sound waves—and stored in the computer to later processing and playback.
MIDI Devices
MIDI (Musical Instrument Digital Interface) is a system designed to transmit information between electronic musical instruments. A MIDI musical keyboard can be attached to a computer and allow a performer to play music that is captured by the computer system as a sequence of notes with the associated timing (instead of recording digitized sound waves). Graphics tablet.
Output Devices
CRT Monitor
The traditional output device of a personal computer has been the CRT (Cathode Ray Tube) monitor. Just like a television set (an older one, anyway) the CRT monitor contains a large cathode ray tube that uses an electron beam of varying strength to “paint” a picture onto the color phosphorescent dots on the inside of the screen. CRT monitors are heavy and use more electrical power than flat panel displays, but they are preferred by some graphic artists for their accurate color rendition, and preferred by some gamers for faster response to rapidly changing graphics.Monitor screen size is measured diagonally across the screen, in inches. Not all of the screen area may be usable for image display, so the viewable area is also specified. The resolution of the monitor is the maximum number of pixels it can display horizontally and vertically (such as 800 x 600, or 1024 x 768, or 1600 x 1200). Most monitors can display several resolutions below its maximum setting. Pixels (short for picture elements) are the small dots that make of the image displayed on the screen. The spacing of the screen’s tiny phosphor dots is called the dot pitch (dp), typically .28 or .26 (measured in millimeters). A screen with a smaller dot pitch produces sharper images. Your computer must produce a video signal that a monitor can display. This may be handled by circuitry on the motherboard, but is usually handled by a video card in one of the computer’s expansion slots; often the slot is a special one dedicated to video use, such as an AGP slot (Accelerated Graphics Port). Video cards are also called video display adapters, and graphics cards. Many video cards contain separate processors and dedicated video memory for generating complex graphics quickly without burdening the CPU. These accelerated graphics cards are loved by gamers.
Flat Panel Monitor
CRT monitor
than ink jet printers. Their speed is rated in pages per minute (ppm). Laser printers are more expensive than ink jets, but they are cheaper to run in the long term if you just need good quality black & white pages.
Other Printers
Laser Printer Multi-function printers are available that not only operate as a computer printer, but also include the hardware needed to be a scanner, photocopier, and FAX machine as well.Dot matrix printers use small electromagnetically activated pins in the print head, and an inked ribbon, to produce images by impact. These printers are slow and noisy, and are not commonly used for personal computers anymore (but they can print multi-layer forms, which neither ink jet or laser printers can).
Sound Output
Computers also produce sound output, ranging from simple beeps alerting the user, to impressive game sound effects, to concert quality music. The circuitry to produce sound may be included on the motherboard, but high quality audio output from a PC usually requires a sound card in one of the expansion slots, connected to a set of good quality external speakers or headphones. Multimedia is a term describing computer output that includes sound, text, graphics, movies, and animation. A sound card is an example of a multimedia output device (as is a monitor that can display graphics).
MEMORY
Computer memory is any physical device capable of storing information temporarily or permanently. For example, Random Access Memory ( RAM ), is a volatile memory that stores information on an integrated circuit used by the operating system, software, and hardware. Memory is the process by which information is encoded, stored, and retrieved. Encoding allows information from the outside world to be sensed in the form of chemical and physical stimuli. Storage is the second memory process and allows for the creation of a stable, more permanent record of encoded information. Finally, the third process is the retrieval of information that has been stored. Such information must be accessed and returned to consciousness or working memory. Depending on the type of information stored, retrieval may be effortless or it may require a more cognitively demanding search through memory.
Memory is internal storage media of computer that has several names such as majorly categorized into two types, Main memory and Secondary memory.
- Primary Memory / Volatile Memory.
- Secondary Memory / Non Volatile Memory.
1. Primary Memory / Volatile Memory:
Primary Memory also called as volatile memory because the memory can’t store the data permanently. Primary memory select any part of memory when user want to save the data in memory but that may not be store permanently on that location. It also has another name i.e. RAM. Random Access Memory (RAM): The primary storage is referred to as random access memory (RAM) due to the random selection of memory locations. It performs both read and write operations on memory. If power failures happened in systems during memory access then you will lose your data permanently. So, RAM is volatile memory. RAM categorized into following types. DRAM SRAM DRDRAM
Random Access Memory (RAM)
RAM stands for Random Access Memory and it is a read/write memory. Information can be written into and read from a RAM. It is a volatile memory. It retains the stored information as long as it is supplied with power. When power supply of computer is switched off or interrupted the stored information in the RAM is lost. RAMs of various capacities are available for example, 1K, 4K, 16K, 64K, 1M, 4M and so on. There are two important types of RAMs that are Static RAM and Dynamic RAM. Static RAMs retain stored information as long as power supply is on. But a Dynamic RAM loses its stored information in a very short time even though the power supply is on. Therefore, Dynamic RAMs have to be refreshed periodically, generally every 2 millisecond. The Dynamic RAMs are cheaper and have high packing density and moderate speed. They consume less power. They are used where large capacity memories are needed. Static RAMs are costlier and consume more power. They do not need refreshing circuits. They have higher speed than Dynamic RAMs. Static RAM and Dynamic RAM are also written as SRAM and DRAM.
ROM (Read Only Memory)
ROM stands for Read Only Memory and it is a permanent type memory. Its contents are not lost when power supply of computer is switched off. The user cannot write into a ROM. Its contents
CD-ROM (COMPACT DISK ROM) CD-ROM stands for Compact Disk Read Only Memory. It is an optical ROM.
2. Secondary Memory / Non Volatile Memory: Secondary memory is external and permanent memory that is useful to store the external storage media such as floppy disk, magnetic disks, magnetic tapes and etc cache devices. Secondary memory deals with following types of components. Read Only Memory (ROM) : ROM is permanent memory location that offer huge types of standards to save data. But it work with read only operation. No data lose happen whenever power failure occur during the ROM memory work in computers. ROM memory has several models such names are following. 1. PROM: Programmable Read Only Memory (PROM) maintains large storage media but can’t offer the erase features in ROM. This type of RO maintains PROM chips to write data once and read many. The programs or instructions designed in PROM can’t be erased by other programs. 2. EPROM : Erasable Programmable Read Only Memory designed for recover the problems of PROM and ROM. Users can delete the data of EPROM thorough pass on ultraviolet light and it erases chip is reprogrammed. 3. EEPROM: Electrically Erasable Programmable Read Only Memory similar to the EPROM but it uses electrical beam for erase the data of ROM. Cache Memory: Mina memory less than the access time of CPU so, the performance will decrease through less access time. Speed mismatch will decrease through maintain cache memory. Main memory can store huge amount of data but the cache memory normally kept small and low expensive cost. All types of external media like Magnetic disks, Magnetic drives and etc store in cache memory to provide quick access tools to the users.
Secondary Memory
All computers except very small computer system contain both semiconductor as well as magnetic memory. The semiconductor memory is employed as the main memory or primary memory of the computer. It stores programs and data which are currently needed by the CPU. The magnetic memory is used as the secondary or auxiliary memory. The secondary memory is employed for bulk storage of programs, data and other information. It has much larger capacity than the main memory. It stores system software, assemblers, compilers, useful package, large
data files, etc. The secondary memory is non-volatile in nature. The magnetic memory retains the information stored in it. The magnetic memories such as hard disks and floppy disk are the most common secondary memories used in computer system. Back up memory use to store the copy of the important programs of a computer such as operating system, compilers etc. Floppy disks and magnetic tape can be employed as back up storage. These programs are generally available in the secondary memory but they are copies are also kept in the back up memory so that they can be loaded into the secondary memory in case the original program stored in the secondary memory are lost accidentally or due to any other reason. TYPES OF SECONDARY MEMORY
FLOPPY DISK
A floppy disk is made of flexible plastic that is coated with iron oxide. The flexible disk is placed within a square cardboard jacket, or the jacket is often referred as cartridge. The cardboard jacket gives protection to the outer disk surface. Moreover, it has a liner which gives a wiping action to remove dust particles from the disk surface because it is harmful to disk surface as well as to the read/write head. The disk is loaded in the disk drive along with its jacket. Information is read or written through a small hole in the jacket. The jacket can be easily loaded into and unloaded from a disk drive whenever necessary. The read/write head of a floppy disk make direct contact with the disk surface during processing and that’s why floppy disk gets worn because of its constant use. Floppy disks are generally found in 3, 5.25, 8 inches in diameter. Floppy disks can be coated with iron oxide either one side or both side of the disk. One can record anything on each side of the disk. Floppy disks are cheaper than other types of storage devices. The capacity of disk surface of floppy disk varies depending on their diameter and mode of data transfer. The capacity of a single-sided-single-density 5.25 inch disk surface may only be a little over 100 kilobyte, while the capacity of double-sided-double-density 8 inch disk surface may be almost 2 megabytes.
MAGNETIC DISK OR HARD DISK
This storage device has very much higher storage capacity than floppy disk or other types of storage devices. The principle of operation of hard disk or magnetic disk is similar to that of a gramophone recorder. A magnetic disk is a circular disk coated with magnetic oxide for easy magnetization. A large number of disks are stacked firmly on a common spindle. A motor rotates the spindle at a rapid rate. To access each surface of every disk a read/write head is there that is attached to a common arm. The read/write head can move in between inner most track to outer most track along with the arm. The heads do not touch the disk but float on air cushion at a few microns apart. Arrangement of data in each surface of hard disk can be divided in several tracks and each track can be further divided into several sections called sectors. Each sector has fixed size but the number of sectors in each track may vary. Each sector has specific address for data stored in these sectors. A track in a given sector near the circumference is longer than a track near the center of the disk. If bits are recorded with equal density, some tracks will contain more recorded bit the another. In order to access information from a disk, the disk address of the desired data has to be specified. The disk address is specified in terms of the track number, the surface number, and the sector number. Information is always written from the beginning of a
Memory can be either volatile and non-volatile memory. Volatile memory is a memory that loses its contents when the computer or hardware device loses power. Computer RAM is an example of a volatile memory and is why if your computer freezes or reboots when working on a program, you lose anything that hasn't been saved. Non-volatile memory , sometimes abbreviated as NVRAM, is a memory that keeps its contents even if the power is lost. EPROM is an example of a non-volatile memory.
DIFFERENCE BETWEEN MEMORIES
DIFFERENCE BETWEEN PRIMARY MEMORY AND SECONDARY MEMORY PRIMARY MEMORY
- Primary memory of a computer is purely made of electronic devices either by transistor or capacitor.
- Primary memory can directly communicate with CPU (Central Processing Unit) hence it is called main memory.
- Primary memory is relatively faster than secondary memory.
- Primary memory is needed basically by the system itself for processing functions.
- Primary memory is relatively much costly than secondary memory.
- Primary memory has less memory space as compared to the secondary memory. SECONDARY MEMORY
- Secondary memory is not purely made of electronic devices.
- Secondary memory cannot directly communicate with CPU hence it is called auxiliary memory.
- Secondary memory is comparatively slower than primary memory.
- Secondary memory is needed basically by users for storing of data and information permanently.
- Secondary memory is comparatively much cheaper than primary memory.
- Secondary memory has a huge memory space as compared to primary memory. DIFFERENCE BETWEEN RAM AND ROM RAM (RANDOM ACCESS MEMORY)
- RAM is both read and write enable means users can write into and read from a RAM.
- RAM is volatile in nature means its content gets erased when power supply to the computer is switched off.
- A user can write information in RAM temporarily.
- RAM is necessary for holding of data at the time of processing. ROM (READ ONLY MEMORY)
- ROM is only read enable.
- ROM is very much permanent like such as secondary memory.
- Normally users cannot write anything into ROM other than E2PROM.
- ROM is necessary only at the time of starting up (Booting) of the computer.
- ROM’s contents are written at the time of manufacturing.
- ROM contains functions such as sine, cosine, square root, logarithm, code conversion table, exponential tables, etc. DIFFERENCE BETWEEN STATIC RAM AND DYNAMIC RAM SRAM (STATIC RAM)
- SRAM is called static RAM because each bit of Static RAM remains stored until power supply to the computer goes off.
- For Static RAM each bit is stored in flip-flop.
- Static RAM does not need any extra circuit for maintaining bit value (logic 1 or 0) in flip-flops.
- With respect to same size of Dynamic RAM, Static RAM can store fewer amounts of data.
- Static RAM cells are large with respect to Dynamic RAM cells.
- Static RAM is faster than Dynamic RAM because Static RAM does not need any refreshing circuit before accessing the bits of Static RAM.
- This memory is made of transistors.
- Static RAM is very costly as compared to Dynamic RAM.
- Static RAM has less storage density. DRAM (DYNAMIC RAM)
- DRAM is also called Dynamic RAM, because each bit of Dynamic RAM needs to be refreshed periodically.
- For Dynamic RAM each bit is stored in capacitors.
- Dynamic RAM needs extra circuits for maintaining each bit value.
- With respect to same size of Static RAM, Dynamic RAM can store more amounts of data.
- Dynamic RAM cells are smaller with respect to Static RAM cells.
- Dynamic RAM is slower because it needs refreshing periodically before accessing bits in the cell.
- This memory is made of capacitors.
- Dynamic RAM is relatively much cheaper.
- Dynamic RAM has higher storage density. COMPUTER AND ITS CLASSIFICATION
CLASSIFICATION BASED ON AREA OF APPLICATION
Classification based on area of applications Modern computers depending upon their applications are classified as: - a. Special Purpose Computers b. General Purpose Computers a.) Special Purpose Computers : - A special purpose computer is designed only to meet the requirements of a particular task or application. The instructions needed to perform a particular task are permanently stored into the internal memory, so that it can perform the given task on a single command. It therefore doesn’t possess unnecessary options and is less expensive. b.) b) General Purpose Computers : - A General Purpose computers are designed to meet the needs of many different applications. In these computers, the instructions needed to perform a particular task are wired permanently into the internal memory. When one job is over, instructions for another job can be loaded into the internal memory for processing. This, a general purpose machine can be used to prepare pay-bills, manage inventories, print sales report and so on. CLASSIFICATION BASED ON SIZE AND CAPABILITY Classification digital Computer based on size and Capability Based on size and capability, computers are broadly classified into a. Microcomputers (Personal Computer) A microcomputer is the smallest general purpose processing system. The older pc started 8 bit processor with speed of 3.7MB and current pc 64 bit processor with speed of 4.66 GB. Examples: - IBM PC s, APPLE computers Microcomputer can be classified into 2 types :
- Desktops
- Portables The difference is portables can be used while travelling whereas desktops computers cannot be carried around. The different portable computers are: -
- Laptop
- Notebooks
- Palmtop (hand held)
- Wearable computers Laptop : - this computer is similar to a desktop computers but the size is smaller. They are expensive than desktop. The weight of laptop is around 3 to 5 kg. Notebook : - These computers are as powerful as desktop but size of these computers are comparatively smaller than laptop and desktop. They weigh 2 to 3 kg. They are more costly than laptop. Palmtop (Hand held) : - They are also called as personal Digital Assistant (PDA). These computers are small in size. They can be held in hands. It is capable of doing word processing, spreadsheets and hand writing recognition, game playing, faxing and paging. These computers are not as powerful as desktop computers. Ex: - 3com palmV. Wearable computer : - The size of this computer is very small so that it can be worn on the body. It has smaller processing power. It is used in the field of medicine. For example pace maker to correct the heart beats. Insulin meter to find the levels of insulin in the blood. b). Workstations:- It is used in large, high-resolution graphics screen built in network support, Engineering applications(CAD/CAM), software development desktop publishing Ex: UNIX and Windows NT. b) Minicomputer : - A minicomputer is a medium-sized computer. That is more powerful than a microcomputer. These computers are usually designed to serve multiple users simultaneously (Parallel Processing). They are more expensive than microcomputers. Examples: Digital Alpha, Sun Ultra. c) Mainframe computers : - Computers with large storage capacities and very high speed of processing (compared to mini- or microcomputers) are known as mainframe computers. They support a large number of terminals for simultaneous use by a number of users like ATM transactions. They are also used as central host computers in distributed data processing system. Examples: - IBM 370, S/390. d) Supercomputer : - Supercomputers have extremely large storage capacity and computing speeds which are many times faster than other computers. A supercomputer is measured in terms of tens of millions Instructions per second (MIPS), an operation is made up of numerous instructions. The supercomputer is mainly used for large scale numerical problems in scientific and engineering disciplines such as Weather analysis. Examples: - IBM Deep Blue
Instruction cycle
An instruction cycle (sometimes called a fetch–decode–execute cycle ) is the basic operational process of a computer. It is the process by which a computer retrieves a program instruction from its memory, determines what actions the instruction dictates, and carries out those actions. This cycle is repeated continuously by a computer's central processing unit (CPU), from boot-up to when the computer is shut down. In simpler CPUs the instruction cycle is executed sequentially, each instruction being processed before the next one is started. In most modern CPUs the instruction cycles are instead executed concurrently, and often in parallel, through aninstruction pipeline: the next instruction starts being processed before the previous instruction has finished, which is possible because the cycle is broken up into separate steps. A program in computer consists of sequence of instructions. Executing these instructions runs the program in computer. Moreover each instruction is further divided into sequence of phases. The concept of execution of an instruction through different phases is called instruction cycle. The instruction is divided into sub phases as specified ahead—
- First of all an instruction in fetched (accessed) from memory.
- Then decode that instruction.
- Decision is made for memory or register or I/O reference instruction. In case of memory indirect address, read the effective address from the memory.
- Finally execute the instruction.
Instruction register
In computing, an instruction register (IR) is the part of a CPU's control unit that holds the instruction currently being executed or decoded.[1]^ In simple processors each instruction to be executed is loaded into the instruction register which holds it while it is decoded, prepared and ultimately executed, which can take several steps. Some of the complicated processors use a pipeline of instruction registers where each stage of the pipeline does part of the decoding, preparation or execution and then passes it to the next stage for its step. Modern processors can even do some of the steps out of order as decoding on several instructions is done in parallel. Decoding the op-code in the instruction register includes determining the instruction, determining where its operands are in memory, retrieving the operands from memory, allocating processor resources to execute the command (in scalar processors), etc. The output of IR is available to control circuits which generate the timing signals that control the various processing elements involved in executing the instruction. In the Instruction cycle, the instruction is loaded into the Instruction register after the processor fetches it from the memory location pointed by the Program counter.
