Lecturer 4. Architecture of computer systems.
Purpose:to discuss and give a brief idea on computer hardware.
Plan:
1.Architecture and components of computer systems.
2.Use of computer systems. Data representation in computer systems.
Architecture and components of computer systems.
What is Computer Hardware?You are already aware that a computer system is made up of several different components. Those that can be seen and touched are referred to as the Computer Hardware (or hardware). In other words, the physical equipments that are involved in the function of the computer are called its hardware. The computer hardware is typically divided into four main categories:Processing Devices, Memory Devices, Input/, Output Devices, andStorage Devices.
Processing Devices. The Central Processing Unit (CPU)
The Central Processing Unit is an electronic device which runs computer programs: a set of sequential instructions. It is also called as the Computer Processor or the brain of the computer. Тhere are two major components namely the Control Unit (CU) and the Arithmetic and Logic Unit (ALU). The CU is the circuitry that controls the flow of data through the processor, and coordinates the activities of the other units within it. In a way, it is the "brain within the brain", as it controls what happens inside the processor, which in turn controls the rest of the PC. The ALU is a digital circuit that performs arithmetic and logical operations. The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one, for purposes such as maintaining timers. The processors found inside modern CPUs have very powerful and very complex ALUs; a single component may contain a number of ALUs.
We consider the CPU as the processing device of the computer. You are aware that the CPU contains Control Unit (CU) and an Arithmetic and LogicUnit (ALU). These two components work together to perform the processing operations. On a PC, the CPU usually is contained on a single chip and sometimes is called Microprocessor. In addition to the CU and ALU, a microprocessor usually contains the registers and system clock.
The Control Unit (CU).As you know, a computer program or set of instructions must be stored in memory for a computer to process data. The CPU uses its CU to execute these instructions. Further, the CU directs and coordinates most of the operations of the computer. The speed at which the processor carries out its operations is measured in megahertz (MHz). The higher the number of MHz the faster the computer can process information. The Intel i7, Athlon, Celron, and Duron, Ultra Sparkare some examples for the brands of processors available in the market.
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The Arithmetic and Logic Unit (ALU). ALU performs the arithmetic, comparison, and logical operations. Arithmetic operations include addition (+), subtraction (-), multiplication (*) and division (/). Comparison operations include comparing one data item to another to determine if the first item is greater than (>), equal (=), or less than (<) to the second item. Logical operations work with conditions such as AND, OR, NOT.
Memory Devices. Computer Memory.A character is stored in the computer as a group of 0s and 1s, called a Byte. The size of the memory is measured by the number of bites available. The following equalities give the measuring units of the memory.
| 8 Bits | = 1 | Byte | |
| 1024 | Bytes | = 1 | Kilobyte (1KB) |
| 1024KB | = 1 Megabyte (1MB) | ||
| 1024 MB | = 1 Gigabyte (1 GB) | ||
| 1024 | GB | = 1 | Terabyte (1 TB) |
While performing a processing operation, a processor needs a place to temporarily store instructions to be executed and the data to be used with those instructions. The data and the instructions needed by the CPU are temporarily stored in the Memory. Therefore the memory acts as the internal storage of a computer. The programs that are stored in external storages are loaded into the memory before they start running.
Random Access Memory (RAM). The Random Access Memory (RAM) is a volatile form of a computer memory. This small memory is capable of memorizing temporarily. It can be read and written. That is, you can both write data into RAM and read data from RAM. Together with the CPU, RAM determines the computer's speed. A computer with a large RAM and a CPU can actually run faster than a computer with a powerful CPU but with a low RAM.
Read Only Memory (ROM)
As RAM is volatile, the computers need a non-volatile memory to read larger programs. This is known as the Read Only Memory (ROM). The programs which are needed to start up your computer (Ex: to boot the computer) are stored in ROM.
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Cache.Most of todays computers improve their processing times by using cache (pronounced cash).
Memory cache, also called a cache store or RAM cache, helps speed the processes of the computer by storing frequently used instructions and data thus reducing the access time of data. When the processor needs an instruction or data, it first searches in the cache.
Input Devices.A computer executes instructions and processes data into information and stores the information for future use. Input devices are used to enter instructions and data into the computer.
What is Input?Input is any data or instructions you enter to the memory of a computer. Once input is in memory, the CPU can access it and process the input into output. There are four types of input namely: data, programs, commands, and user responses.
Data.Data is a collection of unorganized facts that can include words, numbers, pictures, sounds, and videos. A computer manipulates and processes data into information, which is useful.
Program.A program is a series of instructions that tells a computer how to perform the tasks necessary to process data into information. Programs are kept on storage media such as a floppy disk (not used now), hard disk, CD-ROM, or DVD-ROM. Programs respond to commands issued by the user.
Command.A Command is an instruction given to a computer program. Commands can be issued by typing keywords or pressing special keys on the keyboard. A keyword is a specific word, phrase, or code that a program understands as an instruction. Some keyboards include keys that send a command to a program when you press them. Instead of requiring you to remember keywords or special keys, many programs allow you to issue commands by selecting menu choices or graphical objects. For examples, programs that are menu driven provide menus as a means of providing commands. Today, most programs have a graphical user interface (GUI) that uses icons, buttons, and other graphical objects to issue commands. However, GUI is the most user friendly way to issue commands
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Input Devices. An Input Device is any hardware component that allows you to enter data, programs, commands, and user responses into a computer. Some of the commonly used input devices are listed below.
Keyboard
Pointing devices
• Mouse
• Trackball
• Joystick
• Touchpad
• Light Pen
Scanners
Voice input systems
Web Cam
Bar code readers
Output Devices. An output device is any computer component capable of conveying information to a user. Some commonly used output devices are listed below.
Display devices
Cathode Ray Tube (CRT) monitors
Liquid Crystal Display (LCD) monitors / Flat-panel displays
LED Monitors
Gas plasma monitors
Printers
- Impact printers
- Daisy Wheel and Dot Matrix printers
Non-Impact Printers
- Ink Jet printers
- Thermal Dye Transfer printers
- Laser printers
Plotters
Audio Devices
Speakers
Headphones
Monitor.The monitor displays the output to the user visually. Therefore it is also called the Visual Display Unit (VDU) or simply the screen. Similar to televisions, the sizes of monitors are varying and often expressed in diagonally measured distance in inches. The technology used with monitors is expanding rapidly and there are two major types of monitors that differ in the technology of visualizing the output to the user. They are Cathode Ray Tube (CRT) monitors, Liquid Crystal Display (LCD) and Light Emitting Displays (LED).
The CRT monitor has more lines of dots per inch, higher the lines more amount of the resolution. It creates the picture by number of rows or lines of the small tiny dots. For an instance the resolution of 1024 x 768 will be sharper than 800 x 600 resolutions.
The LCD consists of two sheets of polarizing material with a liquid crystal solution between them. When an electric current passed through the liquid crystal solution, crystals align so that light cannot pass through them. It is like a shutter either allows light to pass through or blocking the light.
The LED is the latest marketing innovation of display units. It looks similar to LCD and it is also a flat panel display. LED means Light Emitting Diode and relates to the way the display is illuminated. LED monitors still use the same Liquid Crystals as the previous LCD displays. The way the backlight works however with the LED's will lead to a number of improvements in the display.
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Though CRT monitors are much cheaper than LCDs and LEDs, the CRTs consume more power than others
Printer.A computer printer produces a hard copy (permanent human-readable text and/or graphics) of documents stored in electronic form, usually on physical/tangible print media such as paper or transparencies. Many printers are primarily used as local computer peripherals, and are connected by a printer cable to a computer which serves as a document source. Some printers, commonly known as network printers can serve as a hardcopy device to be shared and used by any user among a group of users connected to the network. Individual printers are often designed to support both local and network connected users at the same time. There are several types of printers categorized based on the applied technology of printing text/graphics on the paper.
Impact Printers.Any impact printer forms characters and graphics on a piece of paper by striking a mechanism against in an ink ribbon that physically contacts the papers. Because of the striking activity, impact printers generally are noisy.
Many impact printers do not provide letter-quality print. Letter-Quality (LQ) output is a quality of print acceptable for business letters. Many impact printers produce near letter-quality (NLQ)
print, which is slightly less clear than LQ. NLQ impact printers are used for jobs that require only NLQ, such as printing of mailing labels, envelopes, or invoices.
Impact printers are also ideal for printing multipart forms because they easily can print through many layers of paper. Finally, impact printers are used in many factories and retail counters as they can survive in dusty environments, vibrations, and extreme temperatures.
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