Computing revision

Computing revision

1. Binary

   • 1 = On 0 = Off
   • Everything is represented by binary
   • A group of 8 bits is called a bite
   • Nibble - 4 bits (Half a byte)
   • Byte - 8 bits
   • Kilobyte - 1024 bytes
   • Megabyte - 1024 kilobytes
   • Gigabyte - 1024 megabytes
   • Terabyte - 1024 gigabytes
   • Most computers can handle millions of bits every second
   • Denary is 10 base
   • Binary is 2 base
   • 1+1 = 10 becomes 0 with the 1 carried over
   • If a bit has over 8 bit it becomes an overflow error

2. Hardware

   • CPU - executes the fetch decode execute cycle
   • Memory (RAM) - Stores programs, Operations and data while it is being excutes
   • Storage - (HHD, SSD) - Stores programs and long term files even when they are not in use
   • Bridges is how data is transferred between devices
   • ROM - Read only memory
   • RAM - Random access memory
   • RAM is volatile data
   • Virtual memory - It is a section of volatile memory that is created temporarily in the storage drive for when a computer is running slow
   • ROM contains things such as the BIOS
   • Inputs - mouse, keyboard, webcam, games controller
   • Outputs - screen, printer, speakers, headphones
   • Storage - hard drive
   • Keyboard - used to enter characters and data into computers.
   • Mouse - used to control a pointer on the screen of a computer.
   • Games controller - use a combination of buttons and mini thumb-controlled joysticks.

3. Networks

   • Advantages of networks - Communication, Roaming, Sharing information, Sharing resources, Sharing software
   • Disadvantages - Dependence, Hacking, Hardware, Viruses
   • Bus network - A network that has one main line and others going off to work stations. The main advantages is that it is cheap and easy to install. The disadvantages is that if the main wire goes the whole network does and there can be data collisions.
   • Data collisions - When two bits of data hit in the wires of the network.
   • Ring network - A network that is set up in a ring and all the data goes one way. The advantage is that data can move quickly as all the data runs one way. The disadvantage of this is if one of the wire is faulty the whole network will fail as it is all connected
   • Star network - This is where a switch is placed in the middle of all the computers and has wires coming off to each computer. The advantage of this is that it is very reliable and no data collisions can happen. The disadvantages is that it is very expensive and if the switch fails the whole thing does
   • Wired connection - When a computer is connected by a ethernet cable
   • Wireless connection - When a computer is connected to a router with wireless function and it is within range of the router

4. Databases

   • A persistent store of organised data
   • Most sets of data in a database will have a unique identifier
   • entities - each recorded item
   • attributes - details about the entity
   • field - columns used to capture attributes
   • record - one row of details about an entity
   • table - a set of fields and records
   • Types of data - Integers (Whole number), Floats (Real numbers), Characters (ABC,~@) ,Boolean (True or False)
   • Validation - To prove that what is entered is true/correct
   • Type check - checks the data is in the right format
   • Length check - Checks the data is an acceptable length
   • Presence check - Checks that data has been entered into a field
   • Range check - Checks that a value falls within the specified range
   • Spell check - Looks up words in a dictionary