- CPU is the brain of a computer system a computer performs all major calculations and comparisons inside its CPU. CPU is also responsible for activating and controlling the operations of other units of the computer system hence no other single component of a computer determines its overall performance as much as its CPU
- the two basic components of a CPU are the control unit and the arithmetic logic unit
- control unit (CU) of a computer’s CPU acts as the central nervous systems for all other components of the computer it manages and coordinates the entire computer system including the input and output units it obtains instructions from the program stored in main memory interprets the instructions and issues signals that cause other units of the system to execute them
- arithmetic logic unit (A L U) of a computer’s CPU is the place where actual execution of instructions takes place during data processing
- every CPU has built-in ability to execute a set of machine instructions called its instruction set
- as a computer’s CPU interprets and executes instructions there is movement of information between various units of the computer to handle this process satisfactorily and to speed up rate of information transfer the CPU uses a number of special memory units called registers these registers hold information on a temporary basis and are part of the CPU (not main memory )
- the speed of a processor directly depends on a computer’s clock speed which is the number of pulse produced per second by the built in electronic clock we measure clock speed in megahertz (MHz) or gigahertz (GHz)
- normally we measure the processing speed of personal computers in MHz or GHz that of workstations mini computers, and mainframe systems in MIPS (millions of instructions per second) or B I P S( BILLIONS OF INSTRUCTIONS PER SECOND); AND THAT OF SUPERCOMPUTERS IN M F L O P S ( millions of floating point operations per second) G F L O P S (g i g a flops which refers to a ) billion FLOPS) OR T F L O P S ( T E R A FLOPS WHICH REFERS TO 10 F L O P S )
- Three commonly known processor architectures are CISC (complex instruction set computer), RISC (Reduced instruction set computer), and EPIC (Explicitly parallel instruction computing)
- Multicore processor technology enables building of computers with better overall system performance by handling more work in parallel in this technology a processor chip has multiple cooler running more energy efficient processing cores instead of one increasingly powerful core a multicore chip can run multiple programs/threads at the same time with each core handling a separate program /thread to take advantage of multicore chips we must redesign application so that the processor can run them as multiple threads.
- Instruction and data of a program reside in a temporary storage area mainly when the CPU is executing the program this storage space is known as primary storage main memory or simply memory
- A storage unit of a computer system is characterized and evaluated based on following properties storage capacity access time cost per bit of storage volatile and random access
- Main memory of a computer system consists of several small storage areas called locations or cells each location can store a fixed number of bits called word length of the memory
- Data and instructions move to and from memory as one or more words at a time therefore, even if the electronic circuits used are comparable in speed computers having smaller word length will be slower in operation than computers having larger word length
- In a word addressable computer each numbered address location can store a fixed number characters (equal to its word length in bytes) these computers allocate storage space in multiples of word length on the other hand in a character addressable computer each numbered address can store only a single character (A, B, 1, 2, +, -, ETC)
- Main memory capacity of a computer is the number of bytes that its main memory can store normally we measure main memory capacity in terms of kilobytes (KB), which is equal to 1024(210) bytes of storage megabytes (MB) which is equal to 1,048,576 (220) bytes of storage or gigabytes (GB) which is equal to 1,073,741,824 (230) bytes of storage
- A computer’s main memory uses volatile RAM chips RAM chips are of two types-dynamic and static dynamic RAM (DRAM) uses an external circuitry to periodically “regenerate” or refresh storage charge to retain the stored data on the other hand static ram (SRAM) does not need any special regenerator circuit to retain the stored data
- A special type of RAM called read only memory (ROM) is a non-volatile memory chip in which data is stored permanently usual programs -cannot alter this data there are two types of read-only memory (ROM) – manufacturer-programmed and user programmed the latter is known as programmable read only memory (PROM) because a user can program it.
- Once information is stored in a ROM or PROM chip, a user cannot alter it erasable programmable read only memory (EPROM) chip overcomes this problem by allowing users to reprogram it easily to store new information EPROM chip are of two types- ultra violet EPROM (UVEPROM) and electrically EPROM (EEPROM) EEPROM is also known as flash memory
- Cache memory is an extremely fast small memory between CPU and mani memory whose access time is closer to the processing speed of CPU it acts as a high-speed buffer between CPU and main memory and computer systems use it to store temporarily very active data and instructions during processing
