INTRODUCTION TO COMPUTING

Data Storage

PART IWhat is Computer ?What is Hardware ?What is Software ?What are the Input/ Output Devices ?Von Neumann ArchitectureCPU Introduction to Memory

What is a Computer?

Hardware vs. Software

Common Desktop Hardware

von Neumann Architecture Although specific components may vary, virtually all

modern computers have the same underlying structure known as the von Neumann architecture named after computer pioneer, John von Neumann,

who popularized the design in the early 1950's

The von Neumann architecture identifies 3 essential components1. Input/Output Devices (I/O) allow the user to interact

with the computer2. Memory stores information to be processed as well as

programs (instructions specifying the steps necessary to complete specific tasks)

3. Central Processing Unit (CPU) carries out the instructions to process information

Central Processing Unit (CPU)the CPU is the "brains" of the computer, responsible for controlling its inner workings

made of circuitry – electronic components wired together to control the flow of electrical signals

the circuitry is embedded in a small silicon chip, 1-2 inches square

despite its small size, the CPU is the most complex part of a computer (CPU circuitry can have 100's of millions of individual

components)

commercial examples: Intel Core 2 Duo, AMD Athlon, Motorola PowerPC G4, ARM,

CPU (cont.)the CPU works by repeatedly fetching a

program instruction from memory and executing that instructionindividual instructions are very simple (e.g.,

add two numbers, or copy this data)complex behavior results from incredible

speeda 2.53 GHz Celeron D processor can execute 2.53

billion instructions per seconda 2.93 GHz Core 2 Duo processor can execute

2.93 billion instructions per second

Memorymemory is the part of the computer that stores

data and programs

modern computers are digital devices, meaning they store and process information as binary digits (bits)bits are commonly represented as either 0 or 1bits are the building block of digital memory

by grouping bits together, large ranges of values can be represented

Memory (cont.)modern computers use a combination of memory types, each with its own performance and cost characteristics

main memory (or primary memory) is fast and expensive data is stored as electric signals in circuitry, used to store active data memory is volatile – data is lost when the computer is turned off examples: Random Access Memory (RAM), cache

secondary memory is slower but cheaper use different technologies (magnetic signals on hard disk, reflective spots on CD) memory is permanent – useful for storing long-term data examples: hard disk, floppy disk, compact disk (CD), flash drive

Memory (cont.)higher-end computers tend to have

more main memory to allow for quick access to more data and programs more secondary memory to allow for storing more long-term data

Input/Output (I/O) input devices allow the computer to receive data and instructions from external sources examples: keyboard, mouse, track pad, microphone, scanner

output devices allow the computer to display or broadcast its results examples: monitor, speaker, printer

Software recall: hardware refers to the physical components of computers software refers to the programs that execute on the hardware

a software program is a sequence of instructions for the computer (more specifically, for the CPU) to carry out in order to complete some task e.g., word processing (Microsoft Word, Corel WordPerfect) e.g., image processing (Adobe Photoshop, Macromedia Flash) e.g., Web browsing (Internet Explorer, Mozilla Firefox)

QuestioQuestions ???ns ???

PART IIWhat are bits and Bytes?Boolean OperationsFlip Flop GatesOrganization of Main MemoryHexadecimal NotationMagnetic Disks and TapesRepresentation of Data, Sound , Text ,

Images

Bits and Bit PatternsBit: Binary Digit (0 or 1)Bit Patterns are used to represent

information.NumbersText charactersImagesSoundAnd others

Boolean OperationsBoolean Operation: An operation that

manipulates one or more true/false valuesSpecific operations

ANDORXOR (exclusive or)NOT

Figure 1.1 The Boolean operations AND, OR, and XOR (exclusive or)

GatesGate: A device that computes a Boolean

operationOften implemented as (small) electronic

circuitsProvide the building blocks from which

computers are constructedVLSI (Very Large Scale Integration)

Figure 1.2 A pictorial representation of AND, OR, XOR, and NOT gates as well as their input and output values

Flip-flopsFlip-flop: A circuit built from gates that can

store one bit.One input line is used to set its stored value to 1One input line is used to set its stored value to 0While both input lines are 0, the most recently

stored value is preserved

Figure 1.3 A simple flip-flop circuit

Figure 1.4 Setting the output of a flip-flop to 1

Figure 1.5 Another way of constructing a flip-flop

Hexadecimal NotationHexadecimal notation: A shorthand

notation for long bit patternsDivides a pattern into groups of four bits eachRepresents each group by a single symbol

Example: 10100011 becomes A3

Figure 1.6 The hexadecimal coding system

Main Memory CellsCell: A unit of main memory (typically 8

bits which is one byte)Most significant bit: the bit at the left (high-

order) end of the conceptual row of bits in a memory cell

Least significant bit: the bit at the right (low-order) end of the conceptual row of bits in a memory cell

Figure 1.7 The organization of a byte-size memory cell

Main Memory AddressesAddress: A “name” that uniquely

identifies one cell in the computer’s main memoryThe names are actually numbers.These numbers are assigned consecutively

starting at zero.Numbering the cells in this manner associates

an order with the memory cells.

Figure 1.8 Memory cells arranged by address

Memory TerminologyRandom Access Memory (RAM): Memory

in which individual cells can be easily accessed in any order

Dynamic Memory (DRAM): RAM composed of volatile memory

Measuring Memory CapacityKilobyte: 210 bytes = 1024 bytes

Example: 3 KB = 3 times1024 bytesSometimes “kibi” rather than “kilo”

Megabyte: 220 bytes = 1,048,576 bytesExample: 3 MB = 3 times 1,048,576 bytesSometimes “megi” rather than “mega”

Gigabyte: 230 bytes = 1,073,741,824 bytesExample: 3 GB = 3 times 1,073,741,824 bytesSometimes “gigi” rather than “giga”

Mass StorageOn-line versus off-lineTypically larger than main memoryTypically less volatile than main memoryTypically slower than main memory

Mass Storage SystemsMagnetic Systems

DiskTape

Optical SystemsCDDVD

Flash Drives

Figure 1.9 A magnetic disk storage system

Figure 1.10 Magnetic tape storage

Figure 1.11 CD storage

FilesFile: A unit of data stored in mass storage

systemFields and keyfields

Physical record versus Logical recordBuffer: A memory area used for the

temporary storage of data (usually as a step in transferring the data)

Figure 1.12 Logical records versus physical records on a disk

Representing TextEach character (letter, punctuation,

etc.) is assigned a unique bit pattern.ASCII: Uses patterns of 7-bits to represent

most symbols used in written English textUnicode: Uses patterns of 16-bits to represent

the major symbols used in languages world side

ISO standard: Uses patterns of 32-bits to represent most symbols used in languages world wide

Figure 1.13 The message “Hello.” in ASCII

Representing Numeric ValuesBinary notation: Uses bits to represent a

number in base twoLimitations of computer representations of

numeric valuesOverflow – occurs when a value is too big to be

representedTruncation – occurs when a value cannot be

represented accurately

Representing ImagesBit map techniques

Pixel: short for “picture element”RGBLuminance and chrominance

Vector techniquesScalableTrueType and PostScript

Representing SoundSampling techniques

Used for high quality recordingsRecords actual audio

MIDIUsed in music synthesizersRecords “musical score”

Figure 1.14 The sound wave represented by the sequence 0, 1.5, 2.0, 1.5, 2.0, 3.0, 4.0, 3.0, 0

QuestioQuestions ???ns ???