Software and Data

Software and Data

1. Software

   • Operating System
     • User interface - Needed as an environment for the user to interact with
     • Memory management - transfers programs into and out of memory, allocates free space between programs, and keeps track of memory usage
     • Peripheral management - opens, closes and writes to peripheral devices such as storage attached to the computer
     • Multi-tasking - allows multiple applications to run at the same time
     • Security - provides security through user accounts and passwords
   • Utility programs
     • Security
       • Anti-virus - detects and stops viruses
       • Firewall - can be used to filter between trusted and untrusted networks and prevent programs from communicating through the use of ports.
       • Spyware protection - prevents and detect unwanted spyware program installations and to remove those programs
     • Disk organisation
       • File Transfer - piece of software that connects two computers and allows files to pass from to the other
       • Formatting - Storage drives need to be formatted to be compatible with an OS - so the OS formats it to be compatible
       • Defragmentation - Reorganises files so that individual files and all the free space is put together
     • System maintenance
       • System information and diagnosis - shows overview of system and information about hardware
       • System cleanup tools - tools that clean unwanted data such as unwanted cache
       • Automatic updating - automatically updates apps
   • Types of software
     • Off the shelf software - software that is already available - bugs already discovered etc
     • Custom written software - Specially made for a client - made to meet requirements - testing is an issue -
     • Proprietary software - owned by a company - source code is kept secret so cannot be modified or improved -
     • Open source software - Developed by a community - publicly available - made to do good - quick to spot errors - people dont want to make money - source code can be changed - no copyright claim

2. Units

   • Data needs to be converted to binary format in order for a computer to understand it
   • 1 Byte = 8 bits
   • 1 Kilobyte = 1024 bytes
   • 1 Megabyte = 1024 Kilobytes
   • 1 Gigabyte = 1024 Megabytes
   • 1 Terabyte = 1024 Gigabytes

3. Numbers

   • To convert numbers from denary to binary and vice versa we use a table
   • To add 8 bit binary numbers you use the diagram ->
   • An overflow error occurs when you carry on a 1 after the bit limit. eg the sum is 9 bit not 8 bit
   • Hexadecimal
     • 4 bit number can range from 1 - 15
     • Base 10 (denary) has 10 symbols 0-9
     • In hex numbers after 10 are letters
       • (10 = A) - (11= B) (15 = F)
     • 1. To convert to hexadecimal you first need to convert the number into binary
     • 2. Then you split the table into 2 and replace 128, 64, 32 and 16 with 8, 4, 2 and 1
     • 3. You then add the numbers for each table
     • 4. If one of the numbers is above 10 convert it to a letter
     • 5. Then you put the number in the format eg 5D or A5
   • Hex to denary
     • 1. Make nibble tables (8 4 2 1) for the 2 digits and make a binary number that makes those digits
     • 2. Put the 2 binary nibbles together and convert it to denary
   • Hex is used because large binary numbers are hard to work with and hard to remember

4. Characters

   • Characters are represented by a binary number
   • A character set is a set of codes used to represent characters
   • ASCII
     • Bare minimum of characters
     • It is 7 bits and can't have that many characters
   • Unicode
     • 32 Bits and has a lot more character possibilities

5. Images

   • An image is just a lot of pixels that are programmed by binary
   • Metadata is information about the image that allows the computer to recreate the image from the binary code
   • Colour depth is the number of bits used for each pixel. The more bits the more colours it could be
   • Resolution is the number of pixels per unit (pixel density) - ppi tells us the amount of pixels per inch

6. Sound

   • Sound is analogue
   • Computer needs it in digital form to read it
   • To do this we sample the sound wave at set intervals and record the values
   • The sample rate affects the quality of the sound - A high sample rate = better quality sound
   • The bit rate is the space available for each sample measured in KB/s
   • A high bit rate will increase the quality of the sound

7. Instructions

   • Instructions and data are stored in the same place in binary
   • Each instruction is represented by a different bit pattern that the CPU recognises as an instruction
   • A CPU cannot tell the difference between data and instructions and finds what it expects to find based on the program its running
   • Opcode - mnemonic - Assembly code instruction
   • Operand is the data it is storing or processing
   • Different patterns of opcode mean it is data or an instruction

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