The Basic Organization of Computers Betsy Chacko Assistant

The Basic Organization of Computers Betsy Chacko Assistant Professor in Computer Application St. Mary’s College, Thrissur

Electronic Digital Computers n n based on stored program design processor system n n n CPU memory input/output system n n input/output devices secondary storage

Central Processing Unit n n n manages the instruction-execution cycle FETCH – DECODE – EXECUTE coordinates the activities of other devices

Main Memory n n (fast access) storage device for preserving binary data and instructions memory is divided into units or words each is usually a standard size or fixedlength each memory word has a unique address for random access

Main Memory n Random Access Memory (RAM) n n readable writeable usually volatile (e. g. , Dynamic RAM or DRAM) general storage n Read Only Memory (ROM) n n readable permanent nonvolatile special-purpose storage for data and instructions

The CPU and Main Memory

Inside the CPU

Inside the CPU memory address register

Inside the CPU memory address register memory data register

Inside the CPU memory address register program counter memory data register

Inside the CPU memory address register instruction register program counter memory data register

Inside the CPU memory address register memory data register instruction register program counter arithmetic logic unit

Inside the CPU memory address register instruction register program counter memory data register accumulator (work register) arithmetic logic unit

Inside the CPU memory data register memory address register accumulator (work register) instruction register program counter system clock arithmetic logic unit

FETCH the instruction 1. address of the next instruction is transferred from PC to MAR 2. the instruction is located in memory

FETCH the instruction 3. instruction is copied from memory to MDR

DECODE the instruction is transferred to and decoded in the IR

EXECUTE the instruction control unit sends signals to appropriate devices to cause execution of the instruction

Types of Processor Operations n Data Movement Operations n n n moving data from memory to the CPU moving data from memory to memory input and output n Arithmetic and Logical Operations n n integer arithmetic comparing two quantities shifting, rotating bits in a quantity testing, comparing, and converting bits

Types of Processor Operations n Program Control n n starting a program halting a program skipping to other instructions testing data to decide whether to skip over some instructions

Scale and Performance Factors n modern computer systems are driven by processors fabricated using very largescale integration

Scale and Performance Factors n single-user computer systems personal digital assistants (PDAs) n laptops, notebook computers n desktop computer systems n workstations n n multiuser computer systems