Arithmetic and logical unit perform all the arithmetic and logical operations. Arithmetic operations like addition, subtraction, multiplication and logical operations such as comparisons are performed in ALU. All calculations are performed in the arithmetic and logical unit (ALU) of the computer. ALU also does comparisons and takes decision. Whenever any calculation has to be done, the control unit transfers the required data from the storage unit to the ALU. The ALU can also do logical operations. For example, it can check if the number A is less than, equal to or greater than the number B. After the ALU has performed the calculation or the logical operation, the result is transferred to the storage unit.
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The control unit instructs the computer how to carry out a program instruction. It directs the flow of data between memory and arithmetic logical unit. It controls, co-ordinates the entire computer system. The control unit controls all other units in the computer. The input unit does not know when to receive data and where to put the data in the storage unit after receiving it. The control unit gives the necessary instructions to the input unit. Similarly, the control unit instructs the input unit where to store the data after receiving it from the user. In the same way, it controls the flow of data and instructions from the storage unit to ALU. It also controls the flow of results from ALU to storage unit.
The name itself implies, the personal computers were mainly designed to meet the personal computing requirements of users at working place or in home. It is a non-portable and general purpose computer which can easily fit on a normal size office tables. The personal computers have rapidly changed the work culture and habits of individuals as well as organization. The office work is not rapidly increasing and so the personal computer is almost found on the working desks of several employees in any organization which can also provides the users or individuals or employees with easy and flexible adults for education and entertainments and hence personal computers are now common everywhere.
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Laptop PCs are portable computers with less weight and small enough rate on the lap. They use a keyboard, flat screen liquid crystal display, and a Pentium or Power PC processor. Color displays are also available. They are normally generally smaller than a briefcase that can easily be transported and conveniently used in temporary space. Laptops come with hard disk, CRROM and floppy disk drives. It will run in batteries. Many laptops can be connected to a network. As Laptops use miniature components which have to consume low power and have to be packaged in small volume they cost 3 to 4 times the cost of table top PCs of the same capacity.
Super computers are the most powerful of all computers. They have a high processing speed. Their processing speed lies in the range of 400 to 10,000 MIPS, word length 64 to 96 bit, memory capacity 256 MB, hard disk capacity 1000 MB and more and machine cycle time 4 to 6 ns. It is specially designed to maximize the number of FLOPS. Their FLOPS rating is usually more than 1 gigaflop second. Minicomputers are mainly used for purposes requiring enormous amount of data to be processed within a very short time, whether forecasting, space research, weapons research, atomic research, design of aircrafts, etc., are some of the applications. The best known super computers are PARAM series, CRAY series, CYBER series and FUJITSU series.
Mainframe computer are larger, faster and more expensive than other general purpose computers. These are used to handle huge volumes of data. Their word length may be 48 to 64 bit memory capacity, the hard disk capacity 1000 to 10 GB or more and processing speed 30 to 100 MIPS. These computers even possess and work with more than one processor at the same time. Thus one can see these are multi-user, multiprocessor systems. For mainframe computer very sophisticated operating systems are needed to control and supervise their operation. They are used where large amount of data are to be processed or very complex calculations are to be made and these tasks are beyond the computing capacity of minicomputer.
Minicomputers are larger than the micro computers and are more powerful in terms of processing power. Minicomputers are mainly multiprocessor systems where, many users simultaneously work on the systems. Minicomputers process greater storage capacity and larger memories as compared to microcomputer. These are even capable of handling more input-output device. Their word length is 32 bits. Most minicomputers use Motorola 68030 or 68040 CPU. The processing speed lies in the range 10 to 30 MIPS, memory (RAM) capacity lies in the range 8 MB to 256 MB. The hard disk capacity lies in the range 380 to 3GB, it can support up to 64 or even hundred terminals. It is used for payroll preparation, accounting and scientific computation. High performance workstations with graphics input/output capability use in minicomputer.
Based on its small size and the use of microprocessor, a class of computers is known as micro computers. A microprocessor is a processor whose components namely input, output, CPU are on a single integrated-circuit chip. It is a low-cost and the word length of a microcomputer lies in the range of 8 to 32 bits. These are normally single-microprocessor single-user systems designed for performing basic operations like general purpose calculations, industrial control, instrumentation, educational, training, small business applications, home appliances, commercial equipment control, watches, fuel injection of a car, office automation, playing games, etc. These are mainly used in offices, homes, schools, shops, stores, etc. IBM PCs, Apple Mac, IBM PS/2 are some popular computers of this range.
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Based on the utility of computer, they are classified into general purpose computers and special purpose computes. General purpose computers are designed and constructed to cater almost all the needs of the society. They can perform various operations. They are able to perform according to the programs created to meet different needs. These can be used for a variety of tasks from financial accounting to mathematical calculations, from designing textile prints to controlling machinery. They are also flexible and can be used to work on business and scientific problems. A general purpose computer can solve a much broader class problem specially; a general purpose digital computer is remarkably versatile.
Computers are machines that perform only when instructed. They may operate at incredibly fast speed and perform with unbelievable accuracy. But they are able to act or think on their own. Human being is leading towards a stage, when an artificial intelligent machine could be developed which will even be in a position to think and decide. Recent researches are aimed at designing the logic for the thinking computers for building expert systems and knowledge based systems. This computer is using magnetic bubble memories and other recent developments are on the way. These computers will be based on advances in silicon technology. An architecture which makes use of the changes in the technology and allows an easier and more neutral problem solving is being sought.
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