Understanding Digital Data Representation and Computer Systems - Prof. Willis Boughton, Study notes of Computer Science

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In order to be understood by a computer, data and programs need to be represented appropriately

Coding systems (or coding schemes): represent data and programs

Digital computers: devices that can only understand two states, off and on, represented by the digits 0 and 1 (bits, from binary digits)

Digital data representation: process of representing data in digital form so it can be used by a computer

Computers represent programs and data through binary-based coding schemes

Decimal number system: uses 10 symbols (0, 1, 2, 3, 4, 5, 6, 7, 8, and 9)

Referred to as base 10 since it has 10 digits

Computers use the binary number system, which represents all numbers using just two symbols ( and 1)

Referred to as base 2 since it has 2 digits

Decimal Binary 0 0 1 1 2 10 3 11 4 100 5 101 6 110 7 111 8 1000 9 1001 10 1010 11 1011 12 1100 13 1101 14 1110 15 1111 16 10000

Convert letters into binary numbers and vice versa

ASCII and EBCDIC (pp 58)

ASCII (American Standard Code for Information Interchange): coding system used with PCs EBCDIC (Extended Binary-Coded Decimal Interchange Code): developed by IBM, primarily for mainframe use

Unicode: newer code (32 bits per character is common); universal coding standard that represents text data written in any language

Graphics data: still images usually stored as bitmap, a grid of thousands of dots, called pixels (pp 59)

Each pixel is a binary number

Audio data: digitized samples of analog sounds, with many, many samples taken every second

Each instantaneous sound value is a binary number Data usually compressed without losing quality (MP3)

Video data: a collection of frames, each an individual graphic, with many frames displayed each second

Each graphic pixel is a binary number Data can be very large and usually is compressed

Is the main case of a computer

Houses the processing hardware for that computer, as well as disk drives, memory, the power supply, cooling fans, etc.

For a desktop PC often looks like a rectangular box

For a notebook is the notebook case itself

Central processing unit (CPU): circuitry and components together on a motherboard chip

CPU does almost all the processing for a computer

Also called the microprocessor or just the processor

Can have multiple cores (dual-core)

Multiple CPUs on one chip

Most CPUs are made by Intel and AMD (pp 65)

Intel and AMD processers are pretty much equivalent Have same machine language

Servers typically use different CPUs than desktop

Processing speed: CPU clock speed is measured in megahertz (MHz) or gigahertz (GHz)

1 Hz = 1 clock tick per second CPU executes 1 machine language instruction per tick, approximately Higher CPU clock speed = more instructions processed per second

Other factors (CPU architecture, memory, bus speed, etc.) also affect the processing speed

Word size: the amount of data that a CPU can manipulate at one clock tick; typically 32 or 64 bits

The larger the word size the faster the CPU

RAM (random access memory): the main, working memory of the computer

Where data and instructions are put temporarily while being used Random means every byte can be accessed directly Can be read and written by CPU

Consists of chips on a module plugged into the motherboard

Is volatile; contents are lost when computer is shut off

Registers: highest-speed memory built into the CPU and used by the CPU for processing

ROM (read-only memory): nonvolatile memory that stores data and programs permanently

CPU can only read, not write to Set up by computer's manufacturer Contains Basic Input/Output System (BIOS), the instructions the CPU executes during system boot

Flash memory: nonvolatile for data and programs

CPU can read and write - contents not permanent Some is on motherboard; also on memory sticks, etc. Significantly slower than RAM

Heat in the system unit is a major problem, since CPU especially runs very hot

Cooling techniques:

Fans, usually one on CPU and one on power supply Heat sinks (small components typically made out of aluminum with fins that help to dissipate heat)

Server CPUs may be cooled by water

Expansion slot: a location on the motherboard into which expansion cards are inserted

The more slots available, the more devices you can add to your computer

Expansion card: a circuit board inserted into an expansion slot on a PC s motherboard to add additional functionality or to attach a peripheral device

Also called add-in boards, interface cards, and adapter boards