computer science for MEN

Data Representation

Number Systems

• Humans use base 10 (denary) number system with digits 0-9.
• Programmers use base 2 (binary) number system with values 0 and 1 because computers use switches with on/off positions.
• Binary is the building block of all computer systems.
• Each binary digit is called a bit.

Binary Number System

• Binary uses 1s and 0s with corresponding weights: 128, 64, 32, 16, 8, 4, 2, 1, equivalent to powers of 2 from 2^7 to 2^0.
• To convert binary to denary, add the column values where a 1 appears.

Binary Addition and Subtraction

• One's complement involves inverting each digit in a binary number (1s become 0s and vice versa).
• Two's complement involves inverting each digit and adding 1 to the rightmost bit.
• Two's complement simplifies binary addition and subtraction.
• When using negative numbers with an 8-bit representation, the weightings are -128, 64, 32, 16, 8, 4, 2, 1, with anything above 127 being a negative number, easily created through the two's complement.

Computer Memory

• Memory is measured in bytes.
• Kilobyte (KB) is 1,000 bytes.
• Megabyte (MB) is 1,000,000 bytes.
• Gigabyte (GB) is 1,000,000,000 bytes.
• Terabyte (TB) is 1,000,000,000,000 bytes.
• Petabyte (PB) is 1,000,000,000,000,000 bytes.
• This system is based on powers of 10 which some devices use due to simplicity.
• Actual memory is measured by powers of 2.
• Kibibyte (KiB) is 2^10 bytes (1,024).
• Mebibyte (MiB) is 2^20 bytes (1,048,576).
• Gibibyte (GiB) is 2^30 bytes (1,073,741,824).
• Tebibyte (TiB) is 2^40 bytes (1,099,511,627,776).
• Pebibyte (PiB) is 2^50 bytes (1,125,899,906,842,624).
• The IEC created this system based on the binary system.
• The base 2 system is more accurate and ideal for usage with internal memories.

Hexadecimal Number System

• Hexadecimal (hex) is base 16.
• Weightings are 1048576 (16^5), 65536 (16^4), 4096 (16^3), 256 (16^2), 16 (16^1), 1 (16^0).
• Uses digits 0-9 and letters A-F (A=10, B=11, C=12, D=13, E=14, F=15).
• Each hexadecimal digit represents 4 binary digits (16 = 2^4).

Binary-Coded Decimal (BCD) System

• Uses a 4-bit code to represent each denary digit.
• 0000 = 0, 0001 = 1, 0010 = 2, 0011 = 3, 0100 = 4, 0101 = 5, 0110 = 6, 0111 = 7, 1000 = 8, 1001 = 9.
• 4-bit codes can be stored as a half-byte or two 4-bit codes can form one byte.

ASCII Codes and Unicode

• ASCII (American Standard Code for Information Interchange) was established in 1963 and updated in 1986 and is for use in communication and computer systems.
• Standard ASCII consists of 7-bit codes (0-127 denary or 0-7F hexadecimal).
• Represents letters, numbers, and standard keyboard characters, plus 32 control codes.

Multimedia

Bit-Map Images

• Bit-map images consist of pixels in a 2D matrix.
• At least 8 bits (1 byte) per pixel are needed for a colored image (256 possible colors).
• True color requires 3 bytes per pixel (24 bits), resulting in over a million colors.
• The number of bits used to represent a pixel is called the color depth.
• Bit depth determines the color depth of a pixel; increasing bit depth increases the number of possible colors.
• Scaling images impacts density of pixels.
• Increasing image resolution increases the sharpness of an image
• Higher resolution images result in larger file sizes.
• File size = (width * height * bit depth) in bits, divide by 8 for bytes.

Vector Graphics

• Vector graphics use 2D points to describe lines, curves, and geometric shapes.
• Vector graphics are ideal for logos.

Comparison Between Vector Graphics and Bit-Map Images

• Vector graphics are made of geometric shapes while bit-map images are made of pixels with different colors..
• Modification of vectors require changing the properties of the geometric shapes while bit-maps are altered by modifying pixels to alter the image
• Vector graphics do not require large file sizes while Bit-map images are generally very large
• Vector graphics lack realism due to limited shapes while bit-map images are very realistic due to number of pixels.
• Vector graphic file formats usually are extension .svg,.cgm,.odg while bit-map file formats are usually .jpeg,.bmp,.png.. Images that need to be resized should ideally be done through vectors while realistic imaging should be completed by bit-maps.

Sound Files

• Sound requires a medium to travel through oscillations in particles.
• Human ears detect these changes in air pressure as sound.
• Sound waves are converted from analogue to digital using an ADC (analogue to digital converter.
• The computer filters out quiet noises of frequencies outside hearing range.
• Sound waves are sampled at a given time rate.
• Approximate amplitude values are stored.
• Sampling resolution is the number of bits stored per sound sample.
• Sampling rate is the number of sound samples taken per second.
• The higher the rate or sampling resolution, the higher the quality of sound.

Video

• Videos are made of individual picture frames.
• More frames per second mean better video quality.
• Frame rate refers to the number of frames recorded per second.

File Compression

Lossless File Compression

• Allows the original file to be fully recovered without any data loss.
• Important for files where data loss is unacceptable.
• The original data is not degraded.

Lossy File Compression

• Uses an algorithm to remove unnecessary data.
• Results in some loss of detail.
• Original file is usually impossible to reconstruct.

File Compression Applications

MPEG-3 (MP3)

• Uses audio compression to reduce file sizes by roughly 90%.
• Uses perceptual music shaping to remove frequencies outside human range and softer sounds masked by louder ones.
• Employs a lossy format.
• Quality depends on the bit rate (bits per second used when creating the file).

MPEG-4 (MP4)

• Stores multimedia files (music, videos, photos, animations).
• Can be streamed over the internet without significant quality loss.

Photographic (Bit-Map) Images

• Compression reduces both file size and image quality.
• JPEG uses lossy file compression, reducing raw bit-map image size by a factor of 5 to 15.

Vector Graphics

• Scalable Vector Graphics (.svg) are XML text files, allowing them to be compressed.

RLE (Run-Length Encoding)

• Can compress many file formats.
• It is a lossless compression that reduces the size of strings of identical data.

General Methods of Compressing Files

• There are general methods of compression that are not specialized

Networking

Networking Devices

• ARPAnet (Advanced Research Projects Agency Network) was an early packet-switching WAN (1970s).
• Expanded from the Department of Defense to universities, leading to the internet.
• LANs (Local Area Networks) began appearing as personal devices became more common.
• LANs confined to one building or small area while WANs usually consist of multiple LANs
• MANs (Metropolitan Area Networks) are more common than WANs and include multiple LAN's usually restricted to the size of a city
• WANs can be used by international corporations connecting MANs or LANs across the world

Benefits of Networking

• Sharing of devices (e.g., printers) reduces costs.
• Software licenses are cheaper for networks than stand-alone computers.
• Users can share files and data.
• Access to reliable data from a central source.
• Centralized data and file backups.
• User communication via email and instant messaging.
• Network managers can oversee the network, apply access rights, and restrict network access.

Drawbacks of Networking

• Cabling and servers are expensive initial outlay.
• Managing large networks is complex.
• File server breakdowns affect the whole network.
• Malware can affect entire networks.
• Networks can be characterized as Private or Public

Networked Computers

• LAN cards
• Routers
• Switches
• Wireless Routers
• Cabling
• Software
• Operation and Management of the Network
• Operation of firewalls
• Security Applications Utilities
• Services
• DSL
• Satellite Communication Channels
• Wireless Protocols
• IP Addressing

Private Networks

• Private networks are owned by organizations and usually LANs that have restricted access, the organization is responsible for buying.

Public Networks

• Public networks are publicly owned and let others use them.

WANs and LANs

• LANs are in one building or area.
• LANs consist of computers and devices connected to hubs or switches.
• One hub or switch connects to a router and/or modem.

Wireless LAN

• Wireless LAN's dont use wired connections and connect through infared or wireless methods.
• Devices use WAPs (wireless access points) to access networks from further away.
• WAPs transmit data between the WLAN and wired network structure.
• Users access WLANs through wireless LAN adapters.

Wide Area Networks (WANs)

• WANs connect computers or networks over long distances.
• Multiple LANs can form a WAN through modems.
• WANs use (ATMs) networks as common examples.
• WANs use public communication networks, dedicated or leased lines.
• A typical WAN consists of end systems and intermediate systems.

Network Size Guide

• WAN: 100 km to over 1000 km.
• MAN: 1km to 100km
• LAN 10m to 1000m

Client-Server Networking Models

• Client-server model uses dedicated servers and specific client workstations.
• Client computers connect to server computers.
• Users can access files stored on dedicated servers.
• The server dictates which users can access which files.