Types Of Computers Computers are distinguished on the basis of their processing capabilities o Notebooks o Mobile device Supercomputers are the computers with the most processing power The primary application of supercomputers has been in scientific and military work but their use is growing rapidly in business Desktop personal computer is the typical familiar microcomputer system Thin client systems are desktop computer systems that do not offer the full functionality of a PC Mainframes are not as powerful and generally not as expensive as Notebooks are smaller laptops supercomputers Large corporations where data processing is centralized and large databases are maintained most often use mainframe computers Minicomputers are smaller and less expensive than mainframe computers They are usually designed to accomplish specific tasks such as process control and engineering applications Larger companies gain flexibility by distributing minicomputers in organizational units instead of centralizing at one location Servers typically support computer networks enabling users to share files software peripheral devices and other network resources Server farms are large groups of servers Workstations provide high levels of performance to technical users such as designers and are typically based on RISC reduced instruction set computing architecture Microcomputers or personal computers PCs are the smallest and least expensive category of general purpose computers They may be subdivided into five classifications o Desktops o Thin clients o Laptops Mobile devices as handheld computers often called personal digital assistants PDAs or handheld personal computers The Microprocessor The central processing unit CPU is the center of all computerprocessing activities where all processing is controlled data are manipulated arithmetic computations are performed and logical comparisons are made The CPU consists of the Control unit Arithmetic logic unit ALU Primary storage or main memory The Machine Instruction Cycle The cycle of processing is called the machine instruction cycle and it speed depends on the following four factors of chip design The preset speed of the clock that times all chip activities measured in megahertz MHz millions of cycles per second and gigahertz GHz billions of cycles per second The faster the clock speed the faster the chip The word length which is the number of bits 0s and 1s that can be processed by the CPU at any one time The majority of current chips handle 32 bit word lengths and the Pentium 4 is designed to handle 64 bit word lengths The larger the word length the faster the chip The bus width The wider the bus the physical paths down which the data and instructions travel as electrical impulses the more data can be moved and the faster the processing A bus transfers data is measured in megahertz The physical design of the chip the distance between transistors is known as line width The smaller the line width the more transistors can be packed onto a chip and the faster the chip The Evolution of The Microprocessor Moore s Law Gordon Moore s 1965 prediction that microprocessor complexity would double approximately every two years is based on the following changes Increasing miniaturization of transistors Compacting the physical layout of the chip s components decreasing line width and using better conducting materials The arrangement of the components and their interactions is called computer architecture Computer architecture includes the instruction set and the number of the processors the structure of the internal buses the use of caches and the types of input output I O device interfaces An instruction set is the set of machine instructions that a processor recognizes and can execute Complex instruction set computers CISC and reduced instruction set computers RISC dominate the processor instruction sets of computer architectures o A CISC processor contai ns more than 200 unique coded commands one for virtually every type of operation o The other a more recent approach is RISC processors which eliminate many of the little used codes found in the complex instruction set Primary Storage Primary storage or main memory stores data and program statements for the CPU It has four basic purposes 1 To store data that have been input until they are transferred to the ALU for processing 2 To store data and results during intermediate stages of processing 3 To hold data after processing until they are transferred to an output device 4 To hold program statements or instructions received from input devices and from secondary storage Categories of Memory There are two categories of memory the register which is part of the CPU and very fast and the internal memory chips which reside outside the CPU and are slower The control unit the CPU and the primary storage all have registers Small amounts of data reside in the register for very short periods prior to their use Internal memory is used to store data just before they are processed by the CPU Immediately after the processing it comprises two types of storage space RAM and ROM Random access memory RAM is the place in which the CPU stores the instructions and data it is processing o Dynamic random access memories DRAMs o Synchronous DRAM SDRAM Read only memory ROM is that portion of primary storage that cannot be changed or erased ROM is nonvolatile o Programmable read only memory PROM o Erasable programmable read only memory EPROM