OCR Computing Paper 1

• A network allows devices to communicate and share resources.
• Nodes are devices connected on a network.
• The factors that affect the performance of a network are: bandwidth, latency, error rate, transmission media used, number of people on a network.
• Bandwidth is the limit in how much data can be moved across in a given time.
• Latency is the technical term for ‘delay’.
• [Local Area Network] Network that covers a small geographical area.
• [Wide Area Network] Combination of networks that cover a wide geographical area.
• [MAR - Memory address register] holds the memory address of the current instruction and then the data that it uses ,[ MDR - Memory data register] Holds the actual instruction, and then the data that has been fetched from memory, [PC - Program counter] Holds the address of the next instruction to be executed, [ AC - Accumulator] Holds the result of an instruction before it is transferred to memory.
• Encryption protects a network by securing data so it cannot be accessed without the encryption key.
• Devices and computers can also have their storage and hard disk data encrypted.
• Encryption of transmitted data: Websites using HTTPS encrypt the connection to the server.
• Encryption of individual files: Files can be encrypted individually on a computer using a password that then can only be viewed by people who have the password.
• Encryption of drives: Ordinary computer drives can be encrypted so that a password is needed to access information.
• Passwords stored by websites are almost always stored in an encrypted form, if a hacker obtains the data in the password database, they won’t be able to easily read the passwords.
• Compression is the name given to algorithms which reduce file sizes
• Decompression is the process where compressed data is restored to its original format.
• Two types of compression: Lossy Compression [JPG, GIF, MP3] - Permanently loses some data. Lossless Compression [PNG, TIFF] - will not lose any of the original data, when data is uncompressed it is restored exactly as it was in the original.
• Compression is often used for files and data that are sent via the internet.
• Dictionary compression finds patterns in the original text, encodes each pattern in a dictionary.
• Cache is a small amount of very fast, expensive memory in the CPU - it can be accessed faster than RAM.