The Central Processing Unit: What Goes on Inside the Computer Chapter 4 The Central Processing Unit: What Goes on Inside the Computer

CPU CPU - central processing unit electronic circuitry designed to execute instructions composed of control unit and ALU all computers must have at least one control unit - coordinates and controls all parts of the computer system manages the machine cycle ALU (arithmetic logic unit) - performs required arithmetic and logic operations registers - special-purpose, high-speed, temporary storage associated with CPU

Terms associated with the CPU system unit - case that houses the electronic components of the computer motherboard - circuit board that typically contains the CPU, support chips, RAM, and expansion slots microprocessor - an integrated circuit that contains the control unit and ALU of a CPU

Terms associated with the CPU machine cycle - steps performed by the CPU to execute an instruction fetch, decode, execute, store system clock - internal clock that pulses at a fixed rate to synchronize computer operations instruction set - specific group of instructions a CPU is designed to understand bus - set of electrical paths that transport signals from one part of the system to another bus width - number of bits that can be carried at one time

Processor Speeds microprocessor speeds - usually determined by clock speed measured in megahertz (MHz) and gigahertz (GHz) may also be expressed in MIPS or megaflops cache - very high speed memory used to store instructions that have been recently or frequently used

Strategies to Improve Speed RISC - reduced instruction set approach to processor design parallel processing - multiple processors working simultaneously capable of processing speeds in teraflops strategy used for designing and building supercomputers

Data Representation Everything stored in the computer is represented using the binary system (base 2) - sequences of 0’s and 1’s bit - an single binary digit (0 or 1) byte - a group of 8 bits needed to store a character word - number of bits processed by the CPU as a unit

Larger measures of storage Kilobyte (KB) - about 1,000 bytes megabyte (MB) - about 1 million bytes gigabyte (GB) - about 1 billion bytes terabyte (TB) - about 1 trillion bytes

Collating Codes collating code (coding scheme) - a common scheme for assigning a specific series of bits to a specific character ASCII - most widely used code used by most PC’s EBCDIC - used mostly on IBM mainframes Unicode - uses 2 bytes/character can handle alphabets used throughout the world

Memory Memory - part of the computer that holds program instructions and data currently being used also referred to as - primary storage, primary memory, main memory, internal memory, internal storage closely associated with the CPU composed of RAM and ROM

RAM - random access memory used to store instructions and data for currently active programs can be accessed very quickly by the CPU usually volatile - power must be on to retain contents can be erased and written over 128MB common for current PC’s

ROM - read only memory contains programs and data that are permanently stored can be accessed, but cannot be changed used to store boot routine (activated when computer is turned on) nonvolatile - does not lose its contents when the power is turned off