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Machine Architecture

An Introduction

to

Computer Components

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Major Computer Components

Central Processing Unit (CPU) Bus Main Memory (RAM) Secondary Storage I / O Devices Starting the computer

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Computer Functional Diagram

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CPU

Central Processing Unit The “brain” Controls all other computer functions

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CPU (Continued)

Typeso Intel: 4004, 8008, 8080, 8086, 80186,

80286, 80386, 80486, Pentium, Merced, ?o Motorola: 6800, 6809, 68000, 68020,

68040, 68060, 68080, RISC, ?o DEC: PDP-8/10/11, VAX, Alpha, ARM, ?o AMD: K4, K5, K6, K7, ?o Zilog: Z80, Z800, Z8000 (Still around?)

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CPU (Continued)

Just a collection of fast ON/OFF switches

Forty-million transistors in this space (or less)

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CPU (Continued)

Some MainFrame CPUs are limited by the speed of light.

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The Buss

Different major components are connected by the buss.

A buss is a group of parallel wires (or circuit-board connections) that carry control signals and data between components.

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Main Memory

Main memory is made up of two-state devices.

Two state devices have just two possible states (Wow!). An ON/OFF switch is a two-state device.

In memory, one state stands for 1, the other for 0.

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Main Memory (Continued)

Memory can hold any type of data that can be represented by a combination of two states --- and only those types.

Examples:1 = yes, 0 = no 01 = Red, 10 = Blue, 11 = Green 00 = 0, 01 = 1, 10 = 2, 11 = 3

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Main Memory (Continued)

Memory often made up of capacitors (electron storage devices). “Charged” (“full”) 1, ON, SET. “Discharged” (“empty”)

0, OFF, RESET, CLEARED

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Main Memory (Continued)“The Incredible Shrinking Capacitor”

Technology is constantly improvingo Experience smarter engineerso Smarter engineers smaller deviceso Smaller devices cheaper systemso Cheaper systems more saleso More sales more experience

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Main Memory (Continued) “The Incredible Shrinking Capacitor”

Memory chips now routinely contain 128x220 (“128 Meg”) bits.

“If car-makers built cars the way chip-makers build chips, we’d all drive Mercedes-Benzs that cost $4.95, got 1000 miles to the gallon, and fit in our pockets when we got to our destination.”

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Main Memory ((still) Continued)

Memory is divided into cells, where each cell contains 8 bits. Remember that 8 bits is called a byte.

Each of these cells are numbered. The number is the cell’s address.

The address is the, um, ah, er, well the “address” we use to specify which byte we want to work with.

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Main Memory“Nepenthe: Elixir of Forgetfulness.”

Main memory is volatile (it goes away when you turn off the power).

Capacitors leak charge goes away data is lost.

“If car-makers … and they would disappear as soon as we turned off the engine.”

There are non-volatile memory systems.

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Main MemoryReading & Writing (for ‘rithmetic)

In addition to the circuitry that holds the bits, there are other circuits that:o Get the value of the data held at a

particular address --- READ.o Store data at particular address --- WRITE.

o Some memory is designed so that it cannot be written Read-Only Memory ROMo Many types of ROM are non-volatile.

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Memory Access

Memory at all addresses can be accessed in the same amount of time.

Memory can be accessed in any order, like cuts on a CD (not “Byte0, Byte1, Byte3, …, ByteN” like cuts on a tape).

Access in any order Random Access Random Access Memory RAM

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Secondary Storage

Many Types:o Disks (Random Access)o Tapes (Sequential access)

Persistent storage (Stays when the power goes off)o Programso Data files (binary, text)o System organization (Directory structure)

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I/O

Converts some “real” thing (sound, movement, electrical signal) into bits.

Usually done by specialized “add ons”o Keyboardo Monitoro Soundcard

Sometimes disk and tape drives are considered I/O devices.

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Computer/Peripheral Communication“There be Dragons and Mysteries in these Waters.”

Portso Electronic connections through which data

can enter or leave the computer o Identified by port numbers (like memory

cells are identified by addresses)o Usually each device (keyboard, soundcard,

network card, modem) with be assigned to exclusive use of one or more ports

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Computer/Peripheral CommunicationDoesn’t everyone speak Latin ?

I/O devices normally exchange two things with the computer “Data” --- e.g. bits to and from a

modem --- this is what you want “Protocol” --- coordination between

the computer and the device to insure the data is transmitted correctly --- you don’t see it and you don’t want to.

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Computer/Peripheral Communication“No thanks, I peel my own.”

Protocol insures that the device and the computer “speak the same language.”Parity (must there be an even number

of bits per exchange?) “Endedness” (some computers

transmit numbers from-left-to-right, others from-right-to-left)

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Computer/Peripheral Communication“Let’s not both talk at once”

Usually duplex (two-way) rather than simplex (one-way) Simplex: mail, TV/Radio broadcast.o Half-duplex: two-way communication, but

in communication can occur only in one direction at a time (polite telephone call).

o Full-duplex - allows communication in both directions at the same time.

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Computer/Peripheral Communication Controllers

Special-purpose “CPUs” designed to handle I/O

Free main CPU by taking over comms tasks.

Allow more complex I/O, more devices So effective that many machines are

designed to use controllers even if only one device is connected to a port.

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Computer/Peripheral Communication Parallel and Serial Communication

Parallel - All the bits of a pattern are transferred at the same time, with each bit being transferred on a separate line. Requires multi-wire cables. “Gimme Five!”

Serial - Transmits one bit at a time. Slower, but uses a simpler data path. “Here’s one bit, here’s another bit …”

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Bits, Bytes and Words

A bit is a single 1 or 0; a single choice A byte is 8 bits

o A word is 16 bits or 2 byteso Long word = 4 bytes = 32 bitso Quad word = 8 bytes = 64 bitso Programming languages may use these

terms when organizing data A <what> is 4 bits?? (It’s a small byte.)

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More Bits and Bytes

There are 16-, 32-, and 64-bit machines All of UMBC Unix systems are 32-bits

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Booting the Computer

It refers to the computers start-up procedure.

Comes from the expression “pulling yourself up by your bootstraps”

Starts with instructions stored in the ROM chips. (Why: two reasons.)

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Booting the Computer (continued)

A typical boot sequence:o Test critical components (and maybe all

components).o Turn on and setup critical devices

(console, keyboard, power monitor, operating system storage media)

o Load operating system (usually from disk)o Transfer control to operating system.

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Booting the Computer (continued)The Operating System (O/S)

O/S provides fundamental services for all other tasks:o data storageo I/Oo Program execution

O/S is usually stored on disk, but not always: PalmPilot

Once O/S is running, computer can be fully functional.