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Computing Revision (Spread Sheets a document that you can arrange all your…
Computing Revision
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Binary
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What is binary ?
Binary is a language that computers use for their operations. It uses only uses 2 digits - 1 and 0. That is why the computer's base is 2. We use base 10 (digits 0-9) for our daily life. This is called denary/decimal (for exam purposes it's known as decimal).
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What is an overflow?
Computers all have a predefined range of values that they can store/represent. Therefore, while executing a programme, a computer may reach a number out of its range and it will experience errors and will not able to store the correct answer or calculation.
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Overflow errors
Adding 11 and 01 in binary results in an overflow answer, 100.
The effects of an overflow error can vary.
It might make the program crash or it might just ignore the extra digit on the left and produce an unexpected result (in this case, 2 + 3 = 0!).
Operating Systems
Functions
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Manages Memory-Transfers programs into and out of memory, allocates free space between programs, and keeps track of memory usage
Manage Peripherals-Opens, closes and writes to peripheral devices such as storage attached to the computer
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Examples of Operating Systems
- Mac OS X
- Linux
- Windows
- Android (based on Linux)
- iOS
- Solaris (Not the one in Mont Kiara or from Warframe)
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User Interface
The OS provides a user interface (UI), an environment for the user to interact with the machine. The UI is either graphical or text-based.
Graphical user interface (GUI)
The OS on most computers and smartphones provides an environment with tiles, icons and/or menus. This type of interface is called the graphical user interface (GUI) because the user interacts with images through a mouse, keyboard or touchscreen.
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More information:
Some games, such as Minecraft, also make use of a command line tool which allows the user to bypass the main interface and alter the game’s mechanics or environment.
Managing the CPU
The OS is used to run programs by clicking on an icon, selecting the program from a menu, or typing in an instruction at the command line
When the OS runs a piece of software it has to find the program files on the storage drive, load them into main memory and instruct the CPU to start executing the program from the beginning.
In each case, the OS performs the same sequence of steps:
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4.The CPU program counter is set to the memory location of the first instruction in the program, and execution begins
Managing Memory
The OS manages how main memory is used. It decides:
- how memory is shared between processes
- what happens when there is not enough main memory to get the job done
Multitasking
The OS makes it possible to run several programs at once. Several programs can be stored in RAM at the same time, however only one program at a time is processed by the CPU. Programs can be in one of three states:
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Only one process can be running at any one time. CPUs are extremely fast, so if a program is processed for even a short time it can do quite a lot. The OS decides the best way to swap between running, runnable and waiting processes. It controls which process is being executed by the CPU at any point in time, and shares access to the CPU between processes. The job of working out when to swap processes is known as scheduling.
Scratch
IF Statement:
A programming conditional statement that, if proved true, performs a function or displays information.
Nested IF Statement:
A nested IF statement is an IF statement that is the target of another if statement. Nested if statements means an if statement inside another if statement.
How a piece of code works:
Writing code tells the computer what to do, but it's not quite that simple.
A computer can only understand two distinct types of data: on and off. In fact, a computer is really just a collection of on/off switches (transistors). Anything that a computer can do is nothing more than a unique combination of some transistors turned on and some transistors turned off. Binary is an example of code, the on is one and the off is zero
Loops:
Loops can make a specific set of actions repeat, as long as they are in the loop