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Data Storage

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Bits and Bit Patterns

Bit: Binary Digit (0 or 1)

Bit Patterns are used to represent

information. Numbers

Text characters

Images Sound

And others

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Boolean Operations

Boolean Operation:An operation thatmanipulates one or more true/false

values

Specific operations

AND

OR XOR (exclusive or)

NOT

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The Boolean operations AND, OR, andXOR (exclusive or)

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Gates

Gate:A device that computes aBoolean operation

Often implemented as (small) electroniccircuits

Provide the building blocks from which

computers are constructedVLSI (Very Large Scale Integration)

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A pictorial representation of AND, OR, XOR, andNOT gates as well as their input and output values

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Hexadecimal Notation

Hexadecimal notation:A shorthandnotation for long bit patterns

Divides a pattern into groups of four bitseach

Represents each group by a single symbol

Example: 10100011 becomes A3

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The hexadecimal coding system

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Main Memory Cells

Cell:A unit of main memory (typically 8 bitswhich is one byte)

Most significant bit: the bit at the left(high-order) end of the conceptual row ofbits in a memory cell

Least significant bit: the bit at the right

(low-order) end of the conceptual row ofbits in a memory cell

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The organization of a byte-sizememory cell

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Main Memory Addresses

Address:A name that uniquely identifiesone cell in the computers main memory

The names are actually numbers. These numbers are assigned consecutively

starting atzero.

Numbering the cells in this mannerassociates an order with the memory cells.

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Memory cells arranged by address

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Memory Terminology

Random Access Memory (RAM):Memory in which individual cells can be

easily accessed in any order Dynamic Memory (DRAM): RAM

composed of volatile memory

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Measuring Memory Capacity

Kilobyte: 210 bytes = 1024 bytes Example: 3 KB = 3 times1024 bytes

Sometimes kibi rather than kilo Megabyte: 220 bytes = 1,048,576 bytes Example: 3 MB = 3 times 1,048,576 bytes Sometimes megi rather than mega

G

igabyte:230

bytes = 1,073,741,8

24bytes Example: 3 GB = 3 times 1,073,741,824

bytes Sometimes gigi rather than giga

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Mass Storage

On-line versus off-line

Typically larger than main memory

Typically less volatile than mainmemory

Typically slower than main memory

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Mass Storage Systems

Magnetic Systems Disk

Tape Optical Systems

CD

DVD

Flash Drives

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A magnetic disk storage system

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Magnetic tape storage

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CD storage

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Files

File:A unit of data stored in massstorage system

Fields and keyfields

Physical record versus Logical record

Buffer:A memory area used for the

temporary storage of data (usually as astep in transferring the data)

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Logical records versus physicalrecords on a disk

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Representing Text

Each character (letter, punctuation, etc.) isassigned a unique bit pattern.

ASCII: Uses patterns of 7-bits to represent mostsymbols used in written English text

Unicode: Uses patterns of 16-bits to represent themajor symbols used in languages world side

ISO standard: Uses patterns of 32-bits to

represent most symbols used in languages worldwide

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The message Hello. in ASCII

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Representing Numeric Values

Binary notation: Uses bits to representa number in base two

Limitations of computer representationsof numeric values Overflow occurs when a value is too big

to be represented

Truncation occurs when a value cannotbe represented accurately

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Representing Images

Bit map techniques Pixel: short for picture element

RGB Luminance and chrominance

Vector techniques Scalable

TrueType and PostScript

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Representing Sound

Sampling techniques

Used for high quality recordings

Records actual audio

MIDI

Used in music synthesizers

Records musical score

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The Binary System

The traditional decimal system is based

on powers of ten.

The Binary system is based on powers

of two.

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The base ten and binary systems

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Decoding the binaryrepresentation 100101

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The binary addition facts

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Compressing Images

GIF: Good for cartoons

JPEG: Good for photographs

TIFF: Good for image archiving

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Compressing Audio and Video

MPEG

High definition television broadcast

Video conferencing

MP3

Temporal masking

Frequency masking