Computer Architecture

Computer Architecture Patrick Marshall

What is computer architecture? • A computer’s architecture is an abstract view of the computer and describes what is it can do- assembly langauge programmers view of the machine.

Data Storage • A computer has seemingly limitless capabilites • In all applications, the computer deals with electronic signals, which can be

Data Storage • Analog signals are continous wave forms in which variations in frequency and amplitude can be use to represent information from sound and data e.g sound of our voice

Data Storage • Digital Signals are described usign two states on(1) or off(0) • Computers are digital and require digital data • What is use to convert from analog to digital?

Data Storage: Binary Digits • Isn’t it amazing, but the seemingly endless potential of computers is based on just two digital states, on and off . • Electronic nature of the computer makes it possible to combine the these two electronic states to represent, letters, numbers, colours and sound.

Data in a Computer • To manipulate stored data in a computer, must have a way of storing and retrieving data. • Data stored temporarily during the processing in Primary Storage eg Random Access Memory (RAM) • Data stored permanently on Secondary Storage eg. Magnetic tape and disk drives.

Computer Organistion • The processor runs the show and is the nucleus (“brain”) of the computer. • The processor is also called the Central Processing Unit (CPU) and has two main units: • Control unit • Arithmetic and logic unit (ALU) • Peforms arthimetic and logic operations • Data can come from memory of input devices • These two units work with RAM to make the processor functional

RAM Storage • Is read and write memory • Is electronic circuitry and has no moving parts, so access is at electronically fast speed • Common technologies are: • Dynamic RAM(DRAM)- slow, must refresh • Static RAM (SRAM)-faster, no refresh needed, but more expensive, needs more spce and power • Ehanced Data Output(EDO) RAM- 50% faster than DRAM

RAM storage (continued) • Sychronous dynamic RAM (SDRAM) enables data transfers at more than twice the speed of previous RAM technologies. • RAMBUS DRAM (RDRAM)- six times faster than SDRAM • Memory chips are installed on: • Single in0line memory modules (SIMMs) • Double in-line memory modules(DIMMs) • SIMMs are cheaper than DIMMs, but has only 32 bit path, DIMMS has 64-bit path to processor.

RAM storage (continued) • Major problem with RAM storage: it is volatile! That is, when electric current is off, data is lost.

RAM storage • All programs and data must be loaded to RAM from secondary storage before programs can be executed and data processed. • Time to access a program intruction or data from RAM is much less than from secondary storage • Processing does not start until the program intruction and data are moved from RAM to the processor • Data in RAM are manipulated by the processor according to the program intructions • A program intruction or data is stored in a specific RAM location called an address

Cache Memory • To facilitate even faster transfer of instruction and data to the processor, cache memory is used • Cache memory increases throughput, the rate at which work can be performed by a computer • Cache is a high speed holding area for program instructions and data,uses internal storage technologies which are faster but more expensive than RAM • Cache holds instructions and data most likely to be needed next by the processor, reducing the slower RAM

ROM, PROM, Flash memory • A special type of internal memory, read-only memory (ROM) , cannot be changed by the user • ROM is non-volatile, and “ hard-wired”,ie designed into the logic of the momery by the manufacturer • Boot up program stored in ROM • Programmable ROM (PROM) is ROM where users can load in read-only programs and data ( usually loaded once only) • Flash memory is a type of PROM which can be altered easily by the user, allowing easier and cheaper ways of upgrades.

Internal Storage (Summary) • Volatile memory • SDRAM • RDRAM • Cache • Register • Non-volatile memory • ROM and PROM • Flash memory

Internal Storage (Summary) • Speed • RAM • Cache are 10 times RAM speed • Registers are 10 times Cache speed • Capacity • Registers holds a few bytes • Cache is intermediate holding area ( fraction of capacity of RAM) • RAM holds programs and data

Computer System Internals

CPU • The control unit is the nucleus of the processor • The control unit functions • Read & interpret progam instructions • Direct operations of internal processor components • Control flow of programs & data in and out of RAM • During program execution, the first in a sequence of program instructions is moved to the control unit, where it is decoded and interpreted by the decoder

CPU • Control Unit also contains: registers • Registers are high speed working storage • Intruction Register • Contains the program intrctions being executed • Program Register • Contains the RAM address of the next instructions to be executed

CPU • The arithmetic & logic unit (ALU) performs all computation ( addition, subtraction, multiplication division) and logical operations. • What are differences between these two equations? • 2+2=5 2+2<5 • Results are placed in a register called the Accumulator

Buses • Buses ar for transporting electrical signals (bits) from one place to another ( just like real buses transport people, who can get on and off at any stop) • In the computing ‘bus stops’ are the control unit, ALU, internal memory, and the device controller, which control operations of peripheral devices • Two types of buses: • Address bus • Data bus

Buses • Source and destination addresses are sent over address bus to access memory locations • Data and instructions are transferred using data bus.

Making the Processor Work • We communicate with the computer by telling them what to do in their language-Machine Language • Computer programming languages like Java, VB, C++ all have to be translated into machine language for execution • Machine language instructions are represented inside a computer as strings of binary digits

The Machine Cycle • Every computer has a machine cycle • Speed of a processor is usually measured by how long it takes to complete a machine cycle • Cycle consists of: • Intruction time (I-time) • Fetch instruction-next instruction to be executed is ‘fetched’ from RAM or cache and loaded into instruction register. • Decode instruction-instruction fetched is decoded and interpreted

The Machine Cycle • Execution time (E-time) • Execute intruction- the instruction is executed using ALU • Place result in memory- the result is placed in memory location specified or in accumulator

Assembly Language for the IBM-PC • title Hello World Program (hello.asm) • ; This program displays "Hello, World!" • dosseg • .model small • .stack 100h • .data • hello_message db 'Hello, World!',0dh,0ah,'$' • .code • main proc • mov ax,@data • mov ds,ax • mov ah,9 • mov dx,offset hello_message • int 21h • mov ax,4C00h • int 21h • main endp • end main

Fetch Instruction Place result in memory I-time Decode Instruction Control Unit E-time Execute Instruction The Machine Cycle

How programs are executed • High level programming language statements • EG: a:=a+1 • b:=a • Program intruction have 2 parts: • Opcode- instructions to be carried out • Operand- data and memory being used

How programs are executed RAM • Assembly language • LDA ACC 8 • INC ACC • STO ACC 8 • LDA ACC 8 • STO ACC 9 Program Register Instrcution Register Accumulator

Processor Design • Most processors and PCs have CISC( Coplex intruction set computer) design • CISC computers offer a wide range of instructions (Add, multiple, compare, move, etc) • RISC ( reduced intruction set computer) desgin have smaller intruction sets, and have higher throughput for certain applications eg those involving graphics • RISC processors shifts computation work from hardware to software • Limitation of RISC offset by increased speed and lower cost

Parallel Processing • Is concept of using many processors in the same computer • Breaks problem into many pieces and solve them on separate processors • Parrallel processing on a large scale( thousands of integrated processing is termed massively parallel processing (MPP))

Decribing the processor • We decribe computers much like we would a person, but we use different characteristics like their word size, speed and the capacoty of their RAM

Word Size • The processor send and receives electrical signals throught it’s electrical bus a word at a time • A word decribes the number of bits which are handled as a unit in the computer system’s bus or during internal processing • Internal processing involves the movement of data or commands between registers, control unit and ALU • Many popular computers have 64-bit internal processing but only a 32-bit path though the bus • Early PC’s had word sizes 8 bits ( 1 byte) • But now we have 64 bit word sizes and up

Processor Speed • We place speed of the computer in context of their design and application • PCs are measured in frequency, MHz • Workstations and mainframes are measured in MIPS • Supercomputers are measures in FLOPS

Processor Speed • PCs • Heart of the PC is its cyrstal oscillator, with a clock cycle • Processor speed is rated by its frequency of oscillation ( no. of clock cycles per second) • Most modern PCs are rated 600-2200 MHz • (IMHz = I million clock cycles per second) • For a 600 MHz PC, one clock cycle is • 1/600,000,000 seconds • One machine cycle usually requires several clock cycles

Processor Speed • MIPS for mainframes and workstations • Stands for millions of instructions per second • Workstations usually operate in range 20-1000 MIPS • FLOPS ( supercomputer) • Floating point operations per second • State-of-the-art supercomputers operate at 500 GFLOPS ( 1 gigaflop = 1 billion FLOPS) to 3 TFLOPS ( 1 teraflop = I trillion flops)

RAM capacity • In terms of the no. of bytes it can store • Usually stated in terms of Megabytes (MB) • One MB = 1,048,576 • Modern PCs range from 32MB to 512MB • Soon we will be talking about RAM in TB • 1 terabyte is about trillion bytes

Inside the PC • The microprocessor ( computer on a chip) is the processor component of the PC. Size is smaller than a postage stamp • System Board • The system board or motherboard is the physical foundation of the Pc • Attached to the system board • Microprocessor • Suppor electronic circuitry • Memory chips • BUS • Expansion slots for linking other circuit boards and peripheral devices

Inside the PC • Before being attached to the boards , the microprocessor and other chips are mounted into a carrier, which have standard pin connections that allow chips to be attached to the system board

Platform types • Motorola manfactures 2 families of microprocessor • M6880X0- we will take a look at this one in more detail • PowerPC • PowerPC gives users tremedous flexibility in that it can run all major indusctry standard platforms • A platform is defined by a combination of hardware and control software • Popular platforms • PowerPc with Apple Mac OS • Intel microprocessor with MS 98, ME, 2000,XP

Platform types • Intel Microprocessors • The system boards for the orignal IBM PC, IBM PC/XT, and IBM Pc compatible microcomputers up till 1984 used intel 8088 microprocessor • IBM PC/AT introduced in 1984 used 80286, Intel 80386, 80486 chips offered even better performaance • Succeeded now by the pentium range

Connecting Peripherals • The system board( with its processor and memory) must be linked to I/O, storage and communications devices to receive data and return the results of processing • To link devices to the PC, we plug its connections into a Port, which provide direct link to the PC’s common bus

Connecting Peripherals • Serial Port • Allows serial transmission of data one bit at a time • Parallel Port • Allows parallel transmission simultaneously • SCSI (Small Computer System Interface) • `faster data transmission and up to 15 devices can be daisy chained to a single SCSI port • USB (Universal Serial Bus) port enables up to 127 devices to be daisy chained • IR port ( infrared) transmits data on infraed light waves

Expansion Slots • ISA ( Industry Standard Architecture • PCI ( Peripheral Component Interconnect) • SCSI bus

Computer Architecture