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An introduction to the representation of data and programs in digital form for use by computers. Topics include the role of coding systems, digital computers, binary number systems, and data compression. It also covers various types of data such as graphics, audio, and video, and the use of machine language and various memory types.
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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