Introduction Computer Architecture Processor and memory architectures What

• Introduction – Computer Architecture • Processor and memory architectures

What is a computer? • Computer is a fast electronic calculating machine that accepts digitized input information, processes it according to a list of internally stored instructions , and produces the resulting output information. • The list of instructions is called a computer program. • The internal storage is called a computer memory.

Computer types • Computers differ in – – Size Cost Computational power Intended use

Computer Architecture • Basic Structure of Computers • Machine instructions and their execution • System software that enables the preparation and execution of programs • Performance issues in the computer.

Functional Units A computer consists of five functionally independent main parts: Input unit Memory Arithmetic and Logic Output Control unit Two types of information are handled by a computer: instructions and data. Instructions are commands that: Govern the transfer of information within a computer as well as between the computer and its I/O devices. Specify the arithmetic and logic operations to be performed. While, Data are numbers and encoded characters that are used as operands by the instructions. (any digital information)

Input unit • Computers accept coded information through input units, which read the data. • ex. Keyboard, joysticks, trackballs , mouse , microphones.

Memory unit • The function of memory unit is to store programs and data. • There are two classes of storage: – Primary storage( main memory : RAM, cache) Fast and expensive , operates at electronic speeds. – Secondary storage( magnetic disks, tapes, optical disks). slow and cheap

Word Length • The number of bits stored or retrieved in one memory access is the word length of a computer.

Addressing scheme • 8 bits 28 • 16 bits 216 • 20 bits 220 = 256 memory locations = 64 K memory locations = 1 M memory locations

Arithmetic and Logic unit (ALU) • Most computer operations are executed in ALU. • Operands are brought from Memory to the CPU registers and operation is performed by ALU.

Output Unit • Sends processed results to the outside world. ex. Printers. • Some units, ex. Graphic displays provide both input and output functions (dual role)

Control Unit • Coordinates the operation of other units by sending control signals to them and sense their states and this is done by generating the timing signals. • Control circuitry is physically distributed through out the machine. • A large set of control lines (wires) carries the signals used for timing and synchronization of events in all units.

Summary • Computer accepts information in the form of programs and data through an input unit and stores it in memory. • Information stored in memory is fetched , under program control, into ALU, where it is processed. • Processed information leaves the computer through an output unit. • All activities inside the machine are directed by the control unit.

Control Unit Arithmetic Logic Unit

CPU Arithmetic/Logic Unit Control Unit Memory I/O Input Output Basic Functional Units of a Computer

CPU data ? Memory instructions

CPU Arithmetic/Logic Unit Control Unit instructions data Memory

CPU Arithmetic/Logic Unit Control Unit 10110101111 (it will be “computed”) (it will be “executed”) Memory

The “fetch-execute cycle” • Fetch the instruction whose address is in the program counter • Increment the PC so it holds the address of the next instruction • Execute the instruction just fetched • Fetch the next instruction • Etc.

Arithmetic/Logic Unit Data Register Control Unit Instruction Register instruction fetch Program Counter instruction Memory

Arithmetic/Logic Unit Data Register Control Unit Instruction Register instruction execute Program Counter data Memory

Arithmetic/Logic Unit Data Register Control Unit Instruction Register instruction fetch 2482 Data Register 04 3300 4102 2482 “Add A to B” Memory

Arithmetic/Logic Unit Data Register Control Unit 04 3300 4102 instruction fetched and PC incremented 2486 Data Register 04 3300 4102 2482 Memory

Arithmetic/Logic Unit Data Register Control Unit instruction decoded Add A to B 2486 Data Register 04 3300 4102 2482 Memory

Arithmetic/Logic Unit 31 Control Unit IR Add A to B execute-load operands 2486 16 data fetch A data fetch B Memory 16 A (3300) 31 B (4102)

Arithmetic/Logic Unit 31 + Control Unit IR Add A to B execute-add operands 2486 16 Memory 16 A (3300) 31 B (4102)

Arithmetic/Logic Unit 47 Control Unit IR Add A to B execute-one register added to the other 2486 16 Memory 16 A (3300) 31 B (4102)

Arithmetic/Logic Unit 47 + Control Unit IR Add A to B execute-store result 2486 16 data store B + A Memory 16 A (3300) 47 B (4102)

Arithmetic/Logic Unit Data Register Control Unit Instruction Register fetch next instruction 2486 Data Register instruction Memory

Read-Only Memories Both SRAM and DRAM chips are volatile, which means that they lose the stored information if power is turned off. Nonvolatile memory that holds the instructions which is used in loading the boot program from the disk. , a memory of this type is called read-only memory (ROM). ROM PROM EEPROM FLASH Memory