computer science notes

Overflow error

Type of error that occurs when a number that is too large and impossible to store is generated. Add 1 to left handside for overflow error.

logical binary shifts

Shift one number to the left or right.

Mac address

a unique address that is given to a computer at the manufacturing stage that can be used to identify the computer.
Address is written in hexadecimal

Analogue Data

A continuous stream of data processed by humans. (TV, Videotape, Photocopier)

Digital data

Discrete data that uses only values 1 and 0 (digital clock, computer, servers)

Registers

a smal component in a computer svstem that is used to temporarily store data.

Pixels

a very small dot of colour that is
displayed with many others to create an image

Resolutions

Dimensions of image

sample resolution

Number of bits used to record each sample.

Calculating size of a file

IMAGE FILE: Width of image x height of image x colour depth of image x number of images in a file (divide by 8 to turn into byte then so on)

SOUND FILE: sample rate x sample resolution x length of soundtrack

Compression

Method that uses an algorithm to reduce the size of a file.

Lossy compression:he data in a file is removed and not restored to its original form after decompression. Specifically, data is permanently removed, which is why this method is also known as irreversible compression. (decreasing resolution)

Lossless compression: method that temporarily alters data to make a smaller file. (instead of storing characters individually, save it once along with its position in text)

Conversion

Negative Binary Numbers

Convert the positive number to binary
Invert the number (change 0 -> 1 & 1->0)
Add 1 to the whole binary number (1010 + 1) Remember rules of binary addition

Binary

A Base 2 number system that uses the values 1 and 0, system on computers uses combinations of 0s and 1s.

DENARY

A Base 10 number system that uses the values 0-9

Hexadecimal

A base 16 number system that uses the values 0-9 and characters A-F.

Converting Denary to Binary

Converting binary to denary

Adding Binary digits

0+0 = 0
1 + 0 = 1
1 + 1 = 0
1 + 1 + 1 = 1

Packets

Data is too large to be transmit from one device to another, therefore data is broken into very small files called packets for it to be transmitted.

3 sections of a packet

Packet switching

The process of transmitting this data is called packet switching. Each data packet is sent individually from one device to another.

Networks

Networks are computer and devices that are joined together using cables or wireless technology.

Router

A router is the device that controls which path will be used to transmit each packet of data.

Data Transmission

Data transmission is the transfer of data from one digital device to another.

Serial data transmission

Parallel Data transmission

Simplex data transmission

Duplex data transmission

Universal Serial Bus (USB)

A Universal Serial Bus (USB) is a common interface that enables communication between devices and a host controller such as a personal computer (PC) or smartphone. It connects peripheral devices such as digital cameras, mice, keyboards, printers, scanners, media devices, external hard drives and flash drives.

USB devices

DETECTING ERRORS IN DATA TRANSMISSION

Data transmission from one device to another is often not a perfect process, data can be lost, changed or added.

Parity check

a method for detecting errors by counting the number of ones or zeros per byte, including a special check bit (parity bit), to see if the value is even or odd.

Parity bit: A Parity bit's purpose is to enforce the selected protocol (if even parity and odd numbers, the parity will make the number even) it is usually the first or larger digit.

Even Parity: even number of 0s and 1s (4,4)
Odd parity: odd number of 0s and 1s ( 5,3)

Check sum

A method that performs a calculate on the data to create a checksum value. The value is then compared to the original value to see if they match.

Both the SENDER and RECEIVER agree on a calculation and a number to divide the SUM of these numbers by. (add then divide by a agreeable number then get a remainder which should be the same in both receiver and sender)

Echo

Sends a copy of transmitted data back to the sender to be compared with the original data sent.

Automatic Repeat Request

A form of error detection using acknowledgements and timeouts.

When an error has been detected after the data is transmitted, it is likely that the data will need to be retransmitted. Either
the sending device will need to ask the receiving device if it received the data correctly, or the receiving device will need to tell the sending device it did or did not receive the data correctly. This will allow the data to be retransmitted if necessary.

Check digit

a type of error detection method that is used for
data entry. A calculation is performed on the data
entered to create a value. Check digit values are
compared to see if the data entered is correct.

Encryption

a method of securing data for storage or transmission that scrambles it and makes it meaningless.

Symmetric Encryption

Assymetric Encryption

more secure than symmetric encryption

Encryption KEY

A type of algorithm that is used to encrypt data to make is meaningless.

Cipher text

Name given to the data after it is scrambled and becomes meaningless.

CPU( Central proccesing UNIT)

A component in the computer system that process data instructions

Microprocessor

An integrated circuit that is able to perform many of the functions of a cpu. A microporccessor will process limited instruction and is built into a system that is designed to perform a very specific task(embedded system)

Embedded System

A computer system that performs a very dedicated function.

(examples: digital alarm clock, traffic light, washing machine)

Fetch-decode-execute cycle

The cycle through which data is processed.

FETCH:This is the stage where instruction is fetched into the CPU.

DECODE: Stage where the instruction is decoded within the CPU

EXECUTE: Stage where the instruction is executed by the CPU

The fetch stage

In order for the data and instructions to be processed, they need to be brought from the RAM into the CPU. This is what happens at the fetch stage of the cycle.

Input Devies

Device that allows data to be entered through a computer system.
(mouse, keyboard, scanner, microphone

- RAM (Random access memory) :

component of a computer that stores programs currently being executed, or data needed for immediate use.

Hard drive

A Storage device that permanently stores data.

Address

A memory location in the RAM

PC (Program counter)

A component of the CPU that stores the address of the next instructions to be processed.

Memory address register (MAR)

A component of the CPU that holds the address of the data or instruction to be located in RAM.

Address Bus

Wires used for the transmission of addresses within the components of a computer.

Memory Data Register (MDR)

Holds the data or instruction that is fetched from the RAM.

Data Bus

Wires used for the transmission of data within the components of a computer.

Current Instruction Register (CIR)

a register that is built into the CU
that holds the current instruction
that is being processed in the CPU.

Control Unit

Component in the CPU that controls all the operations. It decodes the instruction in the Decode stage

Decode Stage

Instruction is received by the CU

Instruction set

A set of commands that can be processed by a certain CPU.

Execute Stage

Actions that are required for the instruction are carried out.

Arithmetic Logic

the component in the CPU that
performs all the mathematical and
logical operations required when
processing data and instructions.

Accumulator (ACC)

a register that is built into the ALU
that stores the result of any interim
calculations.

Control Bus

Wires used for the transmission of control signalswithin the components of a computer.

Arithmetic Logic Unit

3 factors that effect the performance of a CPU

Cores: contains all the components that are used to perform the fetch decode-execute style. (2 cores- 2 cycles)

Clock speed:Number of fetch-decode-execute cycles that can be performed in a second( speed; hertz, one instruction per second is in one second)

Cache: a type of storage that is built into
the CPU, to store the most frequently used data and instructions. (Larger the cache the more storage space to store the insutrction and data it uses most, it can store more of them and will need less time going to the RAM)

Types of devices

Sensor (input device)

Captures data from it’s immediate environment

Acoustic Sensor: measures the level of sound in an environment.

Accelerometer: This type of sensor measures acceleration forces.

Flow: Measures the amount of liquid, gas or steam.

Gas: Measures the presence and concentration of gas within the immediate atmosphere.

Automated System

System designed to work without any human intervention.

Primary storage

Type of storage that is directly accessed by the CPU

Secondary storage

Type of storage that stores data permanently until deleted by the user.It is not directly accessed by the CPU.

Magnetic storage: relies on the properties of magnetism to store data (hard disk)

Optical storage: Uses lasers to read and write data to and from a circular disk(CD,DVD, Blue-ray)

Solid State Storage/Flash memory: Uses transistors, which are wired together without any moving parts.

Semi-conductor chips

an electronic circuit, where
transistors are set on a
semiconductor material, such as
silicon.

Transistors

A device that acts as a gate or signal for electronic signals.

Gates

Control Gate: Controls flow of electric current

Floating Gate: Can store electric charge.

Virtual memory

Another type of storage, it isn’t a component that can be seen or touched, it is an extension of RAM. RAM can crash when it becomes full and will not be able to transfer pager of data to virtual memory, therefore unable to complete ther task it is working on.

cloud storage

Data storage that is owned by a third party and accessed by the user, using internet.

servers

a component that acts as a central resource for the storage of data and applications or providing a service

network

computer devices that are joined together using cables or wireless technology

hardware needed to create a network

Network Interface card (NIC): The component in the computer that is used to connect it to a network.

Media Access Control (MAC) Address: Unique address given to a NIC by the manufacturer. Usually has 6 pairs of numbers separated with a colon or dash and is in hexadecimal.

Router: a network component that examines a data packet to obtain its destination address and then forwards the packet to this address.

Transmission Media: Cables that are used to transfer data in a network

IP Address

Unique address that identifies a device on the internet or a local network

Static IP address: An IP address that doesn't change every time you connect to the network. (DNS Server)

Dynamic IP address: An IP address that can change every time you connect to the network. ( Pc, smartphones, tablet)

software

series of instructions written in a programming languague that perform a function.

System software

manages software and hardware in a computer by allowing communication between these components.

operating system (OS): manages the computer, allows the user to communicate with the computer and lets software run.

utility programs: system software that performs housekeeping activities.

Application software

software that allows the user to perform a useful task

word processor: create written docs
spreadsheet: performs data calculations
database: store and search a set of data
web browser: view and navigate websites

operating system

firmware: instructions that are stored in the ROM and are loaded when the computer starts

bootstrap: first commands loaded when a computer starts, it checks hardware and loads firmware.

Interface

A method by which a user communicates with it's device.

Graphical user interface: has windows, icons,menus.

Command line interface: requires user to enter text as commands.

Natural language interface: allows user to enter text or speak commands.

Interrupts

a signal sent to the processor to tell it that it's attention is required.

Interrupt handler: a program that organizes interrupts based on its priorities

(ISR) Interrupt service routine: program that retrieves and interrupts and performs the task

peripherals and drivers

peripheral: a hardware device, used to input,
store or output data from a computer, that is not directly part of the computer itself.

driver: program that controls a device(keyboard/printer)

High level language

a type of programming that uses human language style words. they are considered portable, they can be written on one computer and run on another.

Low level language

programming that uses a language closer to machine language, could use binary. This is non-portable

Assembly language: code written in mnemonics that
allows direct manipulation of the hardware. It must be converted into binary code to run.

Machine code: uses binary code

interpreter & compiler

interpreter: a translator that converts a high-
level language into a low-level language. It checks one line of code and then executes it before checking the next.

compiler: a translator that converts a high-
level language into a low-level language. It checks all code before running the program.

integrated development environment(IDE)

a program that allows a user to test, run and write a program. it allows provides debugging services, such as (breakpoints, variable watch windows, stepping)

auto-completion: start typing and it suggests options for you to select the correct one.

auto-correction: if you spell a command incorrectly it changes to the right version.

prettyprint: changes the colors of words to spot key terms.

block minimizing: you can make sections of code, minimised so there is less code to read through.

3 types of translators

compiler, assembles, interpreter

Some parts of a computer's memory are marked 'read only', which means their contents cannot be changed or deleted. The contents of ROM are safe when a computer loses power