46 terms

Computer Science

11101110 ----> 238
Converting From Binary To Denary
107 ----> 01101011
Converting From Denary To Binary
1 Kilobyte
Number Of Bits: 2¹⁰
Denary Value: 1 024 bytes
1 Megabyte
Number Of Bits: 2²⁰
Denary Value: 1 048 576 bytes
1 Gigabyte
Number Of Bits: 2³⁰
Denary Value: 1 073 741 824
1 Terabyte
Number Of Bits: 2⁴⁰
Denary Value: 1 099 511 627 776
1 Petabyte
Number Of Bits: 2⁵⁰
Denary Value: 1 125 899 906 842 624
101111100001 ---> 1011 1110 001
B E 1
1000011111101 --> Add 2 0's = 0010 0001 1111 1101
2 1 F D
Converting From Binary To Hexadecimal
4 5 A ---> 0100 0101 1010 --> 010001011010
Converting From Hexadecimal To Binary
Use Of Hexadecimal System
- Memory dumps
- HTML (HyperText Mark-Up Language)
- MAC (Media Access Control)
Memory Dumps
Often used when developing new software or when trying to trace errors in programs. The contents of part of the computer memory can hold the key to help solve many problems.
HyperText Mark-up Language (HTML)
Used when writing and developing web pages. HTML isn't a program language but is simply a mark-up language. A mark-up language is used in the processing, definition and presentation of text.
Media Access Control (MAC)
Refers to a number which uniquely identifies a device on the internet. The MAC address refers to the network interface card which is part of the device.
Universally Administrated MAC Address (UAA)
Most common type of MAC address, set by the manufacturer at the factory. It is rare for a user to want to change this MAC address
Web Addresses
Each character on a keyboard has what is know as a ASCII code (American Standard Code For Information Exchange)
Data Transmission
Data transmission can be either over long or short distances, three factors need to be considered when transmitting data.
- Direction of transmission (One or both directions)
- Method of transmission (How many bits sent at the same time)
- Method of synchronisation between two devices
Simplex Data Transmission
- One direction only
- From sender to receiver (Computer to printer)
Half Duplex Data Transmission
- Both directions but not at the same time
- A -> B or B -> A along same line (Phone conversation)
Full Duplex Data Transmission
- Both directions simultaneously at the same time
- A -> B or B -> along same line (Broadband connection on phone line)
Serial Data Transmission
When data is sent (One bit at a time, over a single wire or channel. (Bits are send one after another in a single stream)
- Works well over long distances
- Data transmitted at slow rate -> compare to serial transmission
- No problem of data arriving at its destination out of synchronisation
Parallel Data Transmission
Several bits of data (Usually 1 byte) sent down several wires or channels at the same time, one wire or channel is used to transmit each bit
- Works well over short distances
- Bits can become 'skewed' no longer synchronised
- Faster than serial
Asynchronous Data Transmission
Data being transmitted in a agreed bit pattern. Data bits (1s & 0s) are grouped together and sent with control bits:
Start - 1 0 1 1 1 1 0 0 1 1 1 0 1 0 1 0 Stop
- Means receiver knows when data starts and ends
- Prevents data from being mixed up
- Without control bits it would be impossible to separate groups of data
Synchronous Data Transmission
Continuous stream of data. The data is joined with timing signals generated by an internal clock, this makes sure the receiver is synchronised with each other.
- Timing must be very accurate
- Faster data transmission method than asynchronous and is used when there is an important issue
Universal Serial Bus (USB)
Is an asynchronous serial data transmission method, has quickly become the standard method for transferring data between a computer and a number of devices.
Benefits & Drawbacks Of A USB
- Devices are automatically detected when plugged in (1)
- Connectors can only fit one way (2)
- Several different data transmission rates are supported (4)
- Max cable length is about 5 metres (2)
- Present transmission rate is limited to less than 500 megabits per second
Parity Checking
Method used to check whether data has been changed or corrupted following transmission from one device or medium to another device or medium.
*Make this odd parity
_ 1 1 0 1 1 0 0 --> *1 1 1 0 1 1 0 0
Automatic Repeat Request (ARQ)
Uses an ACKNOWLEDGEMENT (message sent by receiver indicating the data has been sent correctly) and TIMEOUT (time elapse before an acknowledgement is received). If an acknowledgement isn't sent back to the sender before timeout occurs, the message is automatically resent.
Check to see if data has been changed or corrupted. Data is send in blocks and additional value, also sent at the end of the block data.
Echo Check
When data is sent to another device, the data is sent back again to the sender. The sender compares the two sets of data to check if any errors occurred during the transmission, isn't very reliable if the two sets of data are different.
Internet Service Provider (ISP)
Companies that provide the user with access to the internet. A monthly fee is usually charged for this service. The ISP will set up a user account which will contain a username and a password, most ISP's also give the user an email address.
Internet Protocol (IP) Address
Each device given a unique address know as the IP Address, this is a 32 bit number written in the form:
A home computer is given an IP Address when it connects to the internet. The only IP Addresses that remains fairly unchanged are web servers.
Hypertext Transfer Protocol (HTTP)
Set of rules that must be obeyed when transferring files across the internet. When some form of security is used this is then changed to https.
The letter 's' refers to security, it's slower than http but is usually adopted where sensitive or private data is being transferred across the internet.
Web Browsers
Software which allows a user to display a web page on their screen, browsers interpret or translate the HTML code from websites and show the result of the translation.
- They have a HOME page
- Store user's favourite websites
- Keep a history of the websites visited by the user
NOT Gate
The output, X is 1 if: the input, A, is 0
AND Gate
The output, X is 1 if: both inputs, A and B, are 1
OR Gate
The output, X, is 1 if: either input, A or B, is 1
The output, X, is 1 if: input A AND input B are NOT both 1
The output, X, is 1 if: neither input A nor input B is 1
XOR Gate
The output, X, is 1 if: (input A is 1 AND input B is 0) OR (input A is 0 AND input B is 1)
Operating Systems
Software running in the background of a computer system functions include:
- Human computer interface (HCI)
- Multitasking
- Batch processing
- Error handling
- Memory management
- Input and output control
- Security
- Real-time processing
A signal sent from a device or from software to the processor. This will cause the processor to temporarily stop what it is doing and service the interrupt. Interrupts can occur when:
- Disk drive is ready to receive more data
- Error has occurred, such as a paper jam in a printer
Used in computers as a temporary memory area. Essential in modern day computers since hardware devices operate at much slower speeds than the processor. They are used when streaming videos from the internet, this ensures that the video playback doesn't keep on stopping.
Address Bus
Carries signals relating to addresses between the processor and the memory
*Unidirectional (Signal travels in one direction only)
Data Bus
Sends data between the processor the memory unit and the input/output devices
*Bio-directional (Data can't travel in both directions)
Control Bus
Carries signals relating to the control and coordination of all activities within the computer
*This is regarded as unidirectional and bio-directional due to the internal connections within the computer architecture
von Neumann architecture