cisf hardware

8/11/2019 Cisf Hardware

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Computer Hardware: Basic Definitions

Programming: The planning, scheduling, or performing of a task or event

Computer program: A sequence of instructions for a computer to execute

Computer: An electronic, programmable device that can store, retrieve, and processdata

Modern computers based on the von Neumann architecture

Information: General, abstract knowledge

Data: Information to be processed by a computer

Must be in form computer can understand

Computer converts data to information

Computer system consists of 2 general components:

1. Hardware

2. Software

Units

Unit Quantity symbol

Bit (binary digit) atomic piece of storage/memory b

Byte: 8 bits smallest standard size of storage/data BSecond sHertz Speed H

Common prefixes

Prefix Value Symbol Quantity

Tera 240 = 1, 099, 511, 627, 776 t memory, speedGiga 230 = 1, 073, 741, 824 g memory, speed

Mega 220

= 1, 048, 576 m memory, speedKilo 210 = 1, 024 k memory, speedMilli 103 (0.001) m timeMicro 106 (0.000001) timeNano 109 (0.000000001) n time

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Computer Hardware: Basic Definitions (2)

Approximations

Prefix Approximate Value

Tera 1012

= 1, 000, 000, 000, 000Giga 109 = 1, 000, 000, 000Mega 106 = 1, 000, 000Kilo 103 = 1, 000

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Computer Hardware: Basic Components

Represents physical components

2 general types

Computer proper

1. Main memory

2. Central Processing Unit (CPU)

3. Bus

Peripherals

Add-ons

E.g., printer, DVD drive, hard disk

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Computer Hardware: Memory - Intro

Refers to data storage components of computer

Hierarchy of memory types:

Type Speed Cost NatureRegister fastest most expensive volatileCache volatileRAM slowest least expensive volatileROM nonvolatile

Volatilememory loses its contents when computer is powered off

Stores everything used by the computer:programs, data, ...

Stored electronically

Standard approach uses bi-stable (two-state) device

Transistors used - electronic switches

When voltage applied to base, electricity flows from collector to emitter

Switch is on

No voltage to base, no flow

Switch is off

Transistor represents a bit(binary digit) of data

Each transistor can represent 2 values:

on, and

off

Values represented as 1 and 0

Byteconsidered basic unit of storage

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Computer Hardware: Memory - RAM

RAM stands for Random Access Memory

Consists of a linear sequence of storage locations (cells, words, ...)

Each byte has a unique address, numbered from 0 to total amount of memory - 1

Often, bytes grouped together into words

Memory generally measured in terms of mega or gigabytes

RAM is primary storage area for computer during operation

Often referred to as primary storage, main memory

Stores both programs and data

When power turned off, all switches open

Memory becomes 000000000000000...

Contents must be loaded during operation

Physically exists as an array of cells

Each row and column has a wired connection

To access a particular memory cell, activate the connections for its row andcolumn

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Computer Hardware: Memory - RAM (2)

Types of RAM

Dynamic (DRAM)

Electricity stored in a capacitorTransistor controls amount (voltage) stored

If greater than about 50% capacity 1

If less than about 50% capacity 0

Capacitors lose charge over time (msec)

Computer must refreshvalue in each bit on a regular basis

Done thousands of times per second

Hence: dynamicRAM

Static (SRAM)

Uses multiple transistors per bit

Value does not need to be refreshed

Compared to DRAM

1. Faster (no need to refresh)

2. More expensive

3. Larger

Hence, not used for main memory

Typical time to access data: 50 nsec

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Computer Hardware: Memory - ROM

ROM stands for Read Only Memory

Often called BIOS (Basic InputOutput System)

Data permanently stored - cannot be changed Hardwired using diodes

Stores parts of operating system needed to start computer

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Computer Hardware: Seconday Storage - Intro

Secondary storage refers to memory that is not part of the computer proper

Examples:

Disks

Tapes

CDR

DVD

Flash memory

These types of memory are nonvolatile:

They retain their contents when unpowered

Without secondary storage, programs, data, etc. would need to be typed into acomputer every time it was turned on

These devices generally are magnetic or optical in nature

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Computer Hardware: Secondary Storage - Magnetic Devices

1. Disks

Typical disk structure:

Bits stored as alignments of magnetic particles

Microscopic magnetic particles have north and south poles

One alignment corresponds to a 1 bit, the other to a 0 bit

Data bits appear sequentially along a track

Disk addresses consist of track, block, and byte offset

Block size multiple of 512 bytes

Data transfer is a whole block at a time

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Computer Hardware: Secondary Storage - Magnetic Devices (2)

Read/write process: Given a disk address to access

Disk spins

Typically 7200 rpm

8.33 msec per 1 rotation

Position arm over appropriate track

Called seek time

E.g., 0.02 msec to move to adjacent track

Wait until appropriate block rotates under head - latency time (fast) Called (rotational) latency

E.g., 0.02 msec to move to adjacent track

Best case: 0 msec

Worst case: 8.33 msec

Read the block

Called read time

Requires 8.33/nmsec, wheren is number of blocks per track

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Disk pack

Set of disks packaged as a rigid unit

Each arm has 2 read/write heads - one for each adjacent surface

Actuator moves arms as a unit

Disk address will include surface

Cylinder: set of tracks that can be read/written for a given position of theactuator

Data transfers flow through a buffer

Part of memory reserved for data transfers

Usually can hold several disk blocks

Want efficient data transfer

Factors that affect transfer speed:

Physical record structure

File organization

Buffer management

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Disk is a random access device

Can access disk address independently of others

2. Tape

Tape has 8 tracks

Each track stores one bit

Bytes stored sequentially along tape

Tape is sequential access device

Given an address, must pass over all data that precedes it

Significantly slower than disk

Used for long-term storage of files

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Computer Hardware: Secondary Storage - Optical Devices

CDR and DVD basically the same

Structure is similar to disk structure, except have continuous spiral instead of sepa-rate tracks

Bits stored as differences of reflectivity

Laser shines on disk

Light is reflected into a sensor

Bright interpreted as 1, dull as 0

CDROM

Plastic substrate has bumps burned in with laser

Shiny aluminum coated over the substrate

Laser light shining on a bump reflected away from sensor, so appears dark (rep-resenting a 0)

Data cannot be changed

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Computer Hardware: Secondary Storage - Optical Devices (2)

CD-R

Uses a heat-sensitive, translucent dye instead of bumps

When heated, dye becomes opaque

To write a 0, heat spot on CD with write laser

More powerful than read laser

Read laser not strong enough to affect dye

Can only be written once

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Computer Hardware: Secondary Storage - Optical Devices (3)

CD-RW

Uses a phase-change chemical

In crystalline form, is translucent

In amorphous form, is opaque

When melted and cooled quickly, becomes amorphous

When melted and cooled slowly, becomes crystalline

Initially, compound in crystalline form

To write a 0, melt and cool quickly

To overwrite a 0 with a 1, melt and cool slowly

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Computer Hardware: Flash Memory

Flash memory is like ROM on the motherboard

However, it uses an EEPROM - EelectronicallyErasableProgrammable ROM

Using transistors and quantum effects at the atomic level, a charge can be semi-permanantly stored in a memory cell

The charge can be removed at a later date

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Computer Hardware: Representation

1. Integers (whole numbers)

Each digit of a binary integer represents a power of 2

In decimal (base 10), each digit represents a power of 10:182610= 1 103 + 8 108 + 2 101 + 6 100

In binary (base 2), each digit represents a power of 2:101101012= 1 2

7 + 0 26 + 1 25 + 1 24 + 0 23 + 1 22 + 0 21 + 1 20 =1 128 + 0 64 + 1 32 + 1 16 + 0 8 + 1 4 + 0 2 + 1 1 = 18110

Note that the largest value that can be represented is limited by the amount ofstorage allocated

If 1 byte is used for integers, the largest integer that can be represented is

11111111 = 2

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1 = 255 If 2 bytes are used for integers, the largest integer that can be represented is

1111111111111111 = 216 1 = 65535

To convert decimal representation to binary: Cast out 2s

Steps:

(a) Divide decimal representation by 2

(b) Write down the remainder

(c) Repeat the previous 2 steps, using the quotient for the dividend

(d) Continue until quotient is 0(e) Write the remainders in the reverse order in which they were calculated

Example: 5310(a) 53/2 = 26R1

(b) 26/2 = 13R0

(c) 13/2 = 6R1

(d) 6/2 = 3R0

(e) 3/2 = 1R1

(f) 1/2 = 0R1

(g) Answer= 110101

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Computer Hardware: Representation (3)

2. Floating point (real) numbers

Represented using scientific notation:32.746 107 = 327, 460, 000

In the computer, only the values are stored:sign mantissa sign exponent

Since storage is of fixed size, a fixed set of bits are used for the mantissa andexponent

In addition, the decimal point is assumed to be in a specific location

For example (base 10):

(a) Assuming decimal is in front of first digit of mantissa

(b) 4 digits for mantissa(c) 2 digits for exponent

327, 460, 000 =.32746 109 +3274 + 09

This leads to loss of precision(inability to represent all digits in original)

It increases the range of values that can be represented:

Largest value: 9999 1099

(As opposed to 9999999 in decimal using 8 digits)

Binary representation is used for mantissa, exponent, and signs in the computer

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3. Characters

There is no direct correlation between printable characters and binary represen-tation

Arbitrary codes are used

ASCII (AmericanStandardCode for InformationInterchange)

Standard code for representing characters

Uses 7 bits

A represented by 6510= 01000001

a represented by 9710= 01100001

1 represented by 4910= 00110001

Note: Character 1 not the same as the integer 1

Unicode

Extension of ASCII

Uses up to 4 bytes

EBCDIC

IBM standard for mainframes

4. Parity bits

Extra bit to help insure data integrity

Odd parity means the number of 1s in a byte will add to an odd number

The parity bit is set to insure this is the case

For example:00110101 10011010100110100 000110100

If an extended byte does not have the proper parity, an error has occured

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5. Hexadecimal

Used to simplify representation of binary values

Hexadecimal is base 16 Requires 16 digits

Uses letters in addition to the digits 0 - 9

hex digit 0 1 2 3 4 5 6 7 8 9 A B C D E Fvalue 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Every byte can be represented by a pair of hex digits

Example:

110100102 is represented as 1101 = 1310=D, 0010 = 210= 2, or D216

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Computer Hardware: Central Processing Unit (CPU)

Brains of computer

Components:

1. Registers Special high-speed memory cells local to the CPU

2. Arithmetic Logic Unit (ALU)

Performs computations

3. Control unit (CU)

Controls operation of the system

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Computer Hardware: Central Processing Unit (CPU) (2)

Operation based on von Neumannarchitecture

1. Computer composed of following systems

(a) Memory(b) CPU

(c) IO system

2. Programs are stored in memory

3. Program statements are executed sequentially

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Computer Hardware: CPU - Registers

Storage local to CPU

High-speed memory directly accessible to CPU components

Examples:1. General purpose registers to hold operands and results of computations

2. Accumulator - Specially designated register for operands and results

3. 0

4. +1

5. -1

6. Memory Address Register (MAR)

Stores address of memory location to be accessed

Must be large enough to store largest address in memory address space

E.g., 4GB= 230 memory requires 31 bits

7. Memory Data Register (MDR)

Stores data to be retrieved from or saved to memory

One or more bytes in width

8. Instruction Register (IR)

Holds instruction being executed Must be large enough to hold largest instruction

E.g., 4, 8, 16 bytes

9. Program Counter (PC)

Holds address (in memory) of next instruction to be executed

Must be large enough to store largest address of memory reserved for holdingprograms

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Computer Hardware: CPU - ALU

Types of operations performed:

Arithmetic

Addition

Subtraction

Logic

AND

1 0

1 1 00 0 0

OR1 0

1 1 10 1 0

NOT

1 00 1

EXCLUSIVE OR

1 0

1 1 00 0 1

Shifts

Shift left

11001010

10010100Shift right

11001010 01100101

Rotate left11001010 10010101

Rotate right11001010 01100101

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Computer Hardware: CPU - ALU (2)

Operands can be loaded from registers, or from elsewhere

Results can be stored into a register, or elsewhere

The control line selects the operation to be performedCan be designed to perform more complex operations

But requires more circuitry

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Computer Hardware: CPU - CU

Manages operation of computer

Operates using following cycle

1. Retrieve instruction from memory(a) This step referred to as a fetch

(b) A copyof the instruction is loaded into the IR

(c) Increment the PC

It now holds the address of the next instruction to be executed

2. Decode the instruction

Each instruction is in binary format

Instructions of form opcode operands

There is one opcode for each specific operation the CPU can perform

Operands may take the form of actual values (e.g., 105, c) or addresses (wherevalues are stored)

Instructions may have from 0 to 3 operands

For example:

10100101 01100000

11010101 00000110

10000101 01100001

8 bit opcode, 8 bit operand

Performsx= y + 6

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Computer Hardware: CPU - CU (2)

The instruction decoder circuitreads the opcode of the instruction

The circuitry of this decoder converts the opcode into signals that carry outthe execution of the instruction; e.g.

To add the contents of 2 registers and store the results into another register To load the value at a particular memory address into the MDR

The signals enable various bus lines and devices needed for the task

3. Execute instruction

The circuitry carries out the task

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Computer Hardware: CPU - Memory Access

Execution may require transfer of data between memory and CU

Fetch (read)

1. Load address into MAR

2. Copycontents of address into MDR

3. A fetch is non-destructive- contents of address are unaffected

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Computer Hardware: CPU - Memory Access (2)

Store (write)

1. Load address into MAR

2. Load value into MDR

3. Copy contents of MDR into address4. A write is destructive- original contents of address are lost

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Computer Hardware: CPU - Cache Memory

To speed up processing, CPU may have cache memory

This is high-speed memory local to CPU

Access time about 10 nsGenerally a few KB in size

Operation based on Principle of Locality:

What has been recently accessed is likely to be accessed again in near future

Used as follows:When CPU needs something from memory

Search cache for itemif not found in cacheretrieve from main memorystore in cache

To see how it improves speed:

Assume memory fetch requires 50 ns

Assume memory fetch requires 10 ns Assume data will be found in cache 60% of the time

Average time to fetch a piece of data:(0.60 10) + (0.4 (10 + 50)) = 6 + 24 = 30 ns on average

Why not use cache for RAM if so fast?

Expensive

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Computer Hardware: CPU - Processing Speed

Speed measured in

Hertz(mega, giga)

This refers to how fast the system clock ticks

MIPS (Millions ofInstructionsPer Second)

May require more than one clock tick per instruction

FLOPS (FLOatingPoint operations per Second)

Considered a more realistic measurement of speed

The system clock controls the speed at which instructions are executed

In general, each major step in CPU takes one clock cycle:

FetchDecode

Execute

Fetch data from memory

Write result to memory

Bus width affects transfer speeds

If bus width is 16 bits, but data is 32 bits, requires 2 memory fetches

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