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Computer Science Study Material and Questions STRUCTURE OF A SIMPLE COMPUTER A Computer is a device for automatically carrying out a-program of instructions. It is a powerful, general-purpose machine because it can be programmed to do a wide variety of computations. In this section we show the important terminology of simple computer. Like all computer systems, it will be capable1, of automatically carrying out calculations as directed by any person who uses it, and the user will be able to give it a series of instructions, called a computer program and written in a programming language, which describe his own computational requirements.
Literally thousands of programming languages have been produced, and one of the more modern of these, called Pascal, after Blaise Pascal (1623-1662), a philosopher, mathematician and inventor who built one of the first automatic adding machines. Pascal was developed in 1970 by Professor Dr. Niklaus Wirth of ETH, Zurich. Switzerland. To carry Out, any particular computation. There are three main steps 1. The user input, his program and data (the data is the information which the program will process to produce the desired results of the computations). 2.
Next, the computer carries out, or' executes the program of instructions
3. Finally, the; results of the, computation, feedback, or output, to the user. TASKS OF COMPUTERS The basic tasks that computers can perform are quite limited and can be divided into three categories! 1. Arithmetic operations (addition, subtraction, multiplication, and division). 2. Comparison operations (determining whether a given value is greater than, equal to, or less than another value). 3. Storage and retrieval operations (such as saving a program on a disk so that is can be used later).
What makes the computer particularly useful to people is its ability to combine these tasks as needed and to perform them with a high degree of speed and reliability. With care, a person can add a hundred numbers or even a thousand numbers and find the correct result, but the chances for making an error in this tedious process are considerable. Also, It is a boring task. This is the kind of job that is well suited to a computer. In addition to performing it quickly arid accurately, the computer can store the result for future use.
HARDWARE Hardware consists of the actual physical components of the computer. The three basic components of a computing system, which are essentially the same regardless of the type of system are: a central processing unit, a primary storage unit, and peripheral devices. 1. The Central Processing Unit The component of the computer system that performs processing function is called the central processing unit (CPU). The CPU is the "brain" of the computer and is composed of two major components: the control unit and the arithmetic/logic unit. The control unit is in charge of the activities of the CPU, It does not process or store data itself, but instructs various parts of the computer in performing these tasks. Instructions given to the computer by the user are interpreted by the control unit, which then sends out signals to circuits within the CPU to
execute these instructions. The appropriate input devices are directed to send the usersupplied data to the computer. The control unit also keeps track of which parts of a program have been executed and which ones remain to be executed. Finally, it collects the output and sends it to the designated output device, such as a monitor screen or a printer. The arithmetic/logic unit (ALU) performs mathematical computations such as addition and multiplication and logical operations. A logical operation is performed by instructing the computer to make a comparison and then to take an action based on the result of that comparison. For example, a program statement might instruct the computer to determine if number X is greater than number Y, and to print X if. this condition is true. If the condition is falsej the program might specify another course of action. Arithmetic and logic operations are the only types of instructions that the ALU is able to execute. 2.
The Primary Storage Unit
The primary storage unit (also referred to as main memory, primary memory, or internal storage) temporarily holds program instruction. data, and the intermediate and final results of processing. It consists of many storage locations, each of which can hold a small amount of information. Each of these storage locations has a unique address associated with it. This address allows the computer to locate items that have been stored in its memory. Large computers have millions of these storage locations. 3.
Peripheral Devices
Peripheral devices can be divided into three general categories: input devices, output devices, and secondary storage devices. Programs and data that are entered into a computer to be processed are called input. The word data refers to facts that have been collected but not organized in any meaningful way. When data is processed, or converted to some meaningful form, the result is information. For example, in a national election, the records of all the votes cast for the office of President are data. When these votes are tabulated and the final totals are determined, the result is information. Input devices are used to enter data into the computer so that it can be processed. There are many input devices; some examples are a terminal keyboard, a mouse, a graphics tablet, and a light pen. A given computer system can have many different input devices. Output devices, such as monitor screens and printer, allow the user to examine the computer's output, or processing results. Displaying output on the screen, gives the user the result in a convenient, readable form; this output is referred to as soft copy. However, these results are lost as soon as something else replaces them on the screen. Printing the results on paper, however, gives the user a way of permanently saving this information so that he or she can refer to it at a later time. This output is called hard copy. As with input devices, a particular computer system can have many different output devices. Computers have only a limited amount of storage space in the primary storage unit because this type of memory is relatively expensive to provide, programs, information, and data that need to be saved for later use can be transferred to secondary storage (also referred to as auxiliary storage). Secondary storage devices allow programs, data, and processing results to be saved on secondary storage media such as magnetic tape or floppy diskettes. Disk and tape drives are commonly used secondary storage devices. When the computer needs to process these items again, they can be transferred back into the primary storage unit of the computer. Although it takes more time, to access items in secondary storage than those in main memory, secondary storage can store enormous quantities of data at a reasonable cost. In addition to being less expensive than primary storage, the amount of secondary storage available can easily be increased. CLASSIFICATIONS OF COMPUTER SYSTEMS
Computers come in a wide variety of sizes and shapes, ranging from tiny hand-held devices to some that are several feet in height and diameter. Over the years, computers have become smaller and smaller, but they have also become increasingly powerful. Computers can be divided into four categories: supercomputers, mainframes, minicomputers, and microcomputers. Generally, these four types differ in price, amount of memory, speed, and processing capabilities. Supercomputers are the fastest, most powerful, and most expensive computers available today. To be considered a supercomputer, a machine must be capable of performing at least 10 million arithmetic operations per second. The Cray-2 computer, developed by Cray Research, Inc., is a supercomputer system that is used mainly in.the scientific areas of weather forecasting, nuclear weapons developments, and energy supply and conservation. For most business applications, the extremely high-speed processing capabilities of a supercomputer are not necessary; a mainframe is adequate.
Minicomputers manufactured today are more powerful than mainframes manufactured in the recent past. In general, minicomputers are lower priced, have smaller memories, and are less powerful than mainframes. They are also generally easier to install than mainframes. Minicomputers are often used in business and schools that do not require the capabilities of a mainframe. The microcomputer is currently the smallest and. least costly type of computer. This is the type of computer often found in small business and in homes arid classrooms. Because of the microcomputer's low cost and the flexibility of available software package (commercially written programs that perform specific tasks such as word processing), its popularity has risen tremendously in the past few years. The primary storage unit of a microcomputer is usually smaller than that of the other types of computers we have discussed. Commonly used auxiliary storage devices on microcomputers are floppy disk drives and hard disk drives. When using a floppy disk drive, the diskette with the needed data must be inserted into the
drive. Hard disks are permanently installed in the computer and can store larger quantities of data; commonly in the 20 to 100 megabyte (millions of bytes) range. The computer can access data stored on a hard disk more quickly than that stored on a floppy disk SOFTWARE Programming is the process of writing instructions (a program) for a computer to use to solve a problem. These instructions must be written in a programming language. A program can be anything from a simple list of instructions that adds three numbers together to a large complex structure with many subsections, which calculates the payroll for a major corporation. Programs and series of programs are referred to as software. Some programs direct the computer in its own internal operations. These are called system programs. Other programs are written to solve users problems. They are referred to as application programs.
SYSTEM PROGRAMS System programs directly affect the operation of the computer. They are designed to facilitate the efficient use of the computer's resources and aid in the development and execution of application programs. In early computer systems, human operators watched over computer operations, decided the order in which programs were run, and prepared the necessary input and output devices needed by a program. But as the processing speeds of CPUs increased, the speed of the human operators remained the same. Time delays and errors caused by human operators became a serious problem. In the 1960s operating systems were developed to overcome this problem. An operating system is a set of system programs that allows system to manage its own operation if such a way that the system's resources are used efficiently.
Literally thousands of programming languages have been produced, and one of the more modern of these, called Pascal, after Blaise Pascal (1623-1662), a philosopher, mathematician and inventor who built one of the first automatic adding machines. Pascal was developed in 1970 by Professor Dr. Niklaus Wirth of ETH, Zurich. Switzerland. To carry Out, any particular computation. There are three main steps 1. The user input, his program and data (the data is the information which the program will process to produce the desired results of the computations). 2.
Next, the computer carries out, or' executes the program of instructions
3. Finally, the; results of the, computation, feedback, or output, to the user. TASKS OF COMPUTERS The basic tasks that computers can perform are quite limited and can be divided into three categories! 1. Arithmetic operations (addition, subtraction, multiplication, and division). 2. Comparison operations (determining whether a given value is greater than, equal to, or less than another value). 3. Storage and retrieval operations (such as saving a program on a disk so that is can be used later).
What makes the computer particularly useful to people is its ability to combine these tasks as needed and to perform them with a high degree of speed and reliability. With care, a person can add a hundred numbers or even a thousand numbers and find the correct result, but the chances for making an error in this tedious process are considerable. Also, It is a boring task. This is the kind of job that is well suited to a computer. In addition to performing it quickly arid accurately, the computer can store the result for future use.
HARDWARE Hardware consists of the actual physical components of the computer. The three basic components of a computing system, which are essentially the same regardless of the type of system are: a central processing unit, a primary storage unit, and peripheral devices. 1. The Central Processing Unit The component of the computer system that performs processing function is called the central processing unit (CPU). The CPU is the "brain" of the computer and is composed of two major components: the control unit and the arithmetic/logic unit. The control unit is in charge of the activities of the CPU, It does not process or store data itself, but instructs various parts of the computer in performing these tasks. Instructions given to the computer by the user are interpreted by the control unit, which then sends out signals to circuits within the CPU to
execute these instructions. The appropriate input devices are directed to send the usersupplied data to the computer. The control unit also keeps track of which parts of a program have been executed and which ones remain to be executed. Finally, it collects the output and sends it to the designated output device, such as a monitor screen or a printer. The arithmetic/logic unit (ALU) performs mathematical computations such as addition and multiplication and logical operations. A logical operation is performed by instructing the computer to make a comparison and then to take an action based on the result of that comparison. For example, a program statement might instruct the computer to determine if number X is greater than number Y, and to print X if. this condition is true. If the condition is falsej the program might specify another course of action. Arithmetic and logic operations are the only types of instructions that the ALU is able to execute. 2.
The Primary Storage Unit
The primary storage unit (also referred to as main memory, primary memory, or internal storage) temporarily holds program instruction. data, and the intermediate and final results of processing. It consists of many storage locations, each of which can hold a small amount of information. Each of these storage locations has a unique address associated with it. This address allows the computer to locate items that have been stored in its memory. Large computers have millions of these storage locations. 3.
Peripheral Devices
Peripheral devices can be divided into three general categories: input devices, output devices, and secondary storage devices. Programs and data that are entered into a computer to be processed are called input. The word data refers to facts that have been collected but not organized in any meaningful way. When data is processed, or converted to some meaningful form, the result is information. For example, in a national election, the records of all the votes cast for the office of President are data. When these votes are tabulated and the final totals are determined, the result is information. Input devices are used to enter data into the computer so that it can be processed. There are many input devices; some examples are a terminal keyboard, a mouse, a graphics tablet, and a light pen. A given computer system can have many different input devices. Output devices, such as monitor screens and printer, allow the user to examine the computer's output, or processing results. Displaying output on the screen, gives the user the result in a convenient, readable form; this output is referred to as soft copy. However, these results are lost as soon as something else replaces them on the screen. Printing the results on paper, however, gives the user a way of permanently saving this information so that he or she can refer to it at a later time. This output is called hard copy. As with input devices, a particular computer system can have many different output devices. Computers have only a limited amount of storage space in the primary storage unit because this type of memory is relatively expensive to provide, programs, information, and data that need to be saved for later use can be transferred to secondary storage (also referred to as auxiliary storage). Secondary storage devices allow programs, data, and processing results to be saved on secondary storage media such as magnetic tape or floppy diskettes. Disk and tape drives are commonly used secondary storage devices. When the computer needs to process these items again, they can be transferred back into the primary storage unit of the computer. Although it takes more time, to access items in secondary storage than those in main memory, secondary storage can store enormous quantities of data at a reasonable cost. In addition to being less expensive than primary storage, the amount of secondary storage available can easily be increased. CLASSIFICATIONS OF COMPUTER SYSTEMS
Computers come in a wide variety of sizes and shapes, ranging from tiny hand-held devices to some that are several feet in height and diameter. Over the years, computers have become smaller and smaller, but they have also become increasingly powerful. Computers can be divided into four categories: supercomputers, mainframes, minicomputers, and microcomputers. Generally, these four types differ in price, amount of memory, speed, and processing capabilities. Supercomputers are the fastest, most powerful, and most expensive computers available today. To be considered a supercomputer, a machine must be capable of performing at least 10 million arithmetic operations per second. The Cray-2 computer, developed by Cray Research, Inc., is a supercomputer system that is used mainly in.the scientific areas of weather forecasting, nuclear weapons developments, and energy supply and conservation. For most business applications, the extremely high-speed processing capabilities of a supercomputer are not necessary; a mainframe is adequate.
Minicomputers manufactured today are more powerful than mainframes manufactured in the recent past. In general, minicomputers are lower priced, have smaller memories, and are less powerful than mainframes. They are also generally easier to install than mainframes. Minicomputers are often used in business and schools that do not require the capabilities of a mainframe. The microcomputer is currently the smallest and. least costly type of computer. This is the type of computer often found in small business and in homes arid classrooms. Because of the microcomputer's low cost and the flexibility of available software package (commercially written programs that perform specific tasks such as word processing), its popularity has risen tremendously in the past few years. The primary storage unit of a microcomputer is usually smaller than that of the other types of computers we have discussed. Commonly used auxiliary storage devices on microcomputers are floppy disk drives and hard disk drives. When using a floppy disk drive, the diskette with the needed data must be inserted into the
drive. Hard disks are permanently installed in the computer and can store larger quantities of data; commonly in the 20 to 100 megabyte (millions of bytes) range. The computer can access data stored on a hard disk more quickly than that stored on a floppy disk SOFTWARE Programming is the process of writing instructions (a program) for a computer to use to solve a problem. These instructions must be written in a programming language. A program can be anything from a simple list of instructions that adds three numbers together to a large complex structure with many subsections, which calculates the payroll for a major corporation. Programs and series of programs are referred to as software. Some programs direct the computer in its own internal operations. These are called system programs. Other programs are written to solve users problems. They are referred to as application programs.
SYSTEM PROGRAMS System programs directly affect the operation of the computer. They are designed to facilitate the efficient use of the computer's resources and aid in the development and execution of application programs. In early computer systems, human operators watched over computer operations, decided the order in which programs were run, and prepared the necessary input and output devices needed by a program. But as the processing speeds of CPUs increased, the speed of the human operators remained the same. Time delays and errors caused by human operators became a serious problem. In the 1960s operating systems were developed to overcome this problem. An operating system is a set of system programs that allows system to manage its own operation if such a way that the system's resources are used efficiently.
