# Unit 2: Computer Science

Mind Map by AdamHDGaming, updated more than 1 year ago
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Mind Map on Unit 2: Computer Science, created by AdamHDGaming on 11/07/2014.

## Resource summary

Unit 2: Computer Science
1 Binary
1.1 Binary describes a numbering scheme in which there are only two possible values for each digit: 0 and 1. The term also refers to any digital encoding/decoding system in which there are exactly two possible states.In digital data memory, storage, processing, and communications, the 0 and 1 values are sometimes called "low" and "high," respectively.
1.2 A hexadecimal number use the base 16 and therefore there are 16 digits instead of 10 which we are most used to. The 16 digits are 1 2 3 4 5 6 7 8 9 a b c d e f 0. If you want to turn a decimal number into a hexadecimal one, you should be aware that 10 in hexadecimal means 16 in decimal. 100 in hexadecimal means 16 * 16 in decimal. Other examples are: 1-9 hex is 1-9 dec a hex is 10 dec b hex is 11 dec c hex is 12 dec d hex is 13 dec e hex is 14 dec f hex is 15 dec 10 hex is 16 dec 11 hex is 17 dec and so on This is the same for binary digits but instead of using the base 16 as in hexadecimal or 10 as in decimal, it use the base 2, and there are only two digits, 0 and 1. so: 1 bin is 1 dec 10 bin is 2 dec 11 bin is 3 dec 100 bin is 4 dec 101 bin is 5 dec 110 bin is 6 dec 111 bin is 7 dec 1000 bin is 8 dec Comparing all three systems, Dec: 10 is 10 pow 1 => 10 100 is 10 pow 2 => 100 1000 is 10 pow 3 => 1000 Hex 10 is 16 pow 1 => 16 100 is 16 pow 2 => 16*16 (I
2 Memory
2.1 Ram
2.1.1 Rom
2.1.1.1 Rom is non volitile which means if store something on it and switch the machine off it stays on there
2.1.2 Ram Is volatile memory which means that once the machine is switched off it delete everything on it
2.2 Cache
2.2.1 Cache memory, also called CPU memory, is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM.
2.3 Flash
2.3.1 Flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. Introduced by Toshiba in 1984, flash memory was developed from EEPROM (electrically erasable programmable read-only memory)
2.4 The Need For Virtual Memory
2.4.1 Virtual memory is a component of most operating systems, such as MAC OS, Windows and Linux. Virtual memory has a very important role in the operating system. It allows us to run more applications on the system than we have enough physical memory to support. Virtual memory is simulated memory that is written to a file on the hard drive. That file is often called page file or swap file. It's used by operating systems to simulate physical RAM by using hard disk space. To understand how virtual memory works we have to go back in time, before virtual memory even exited. In the days of Windows version 1 or 2, we actually couldn't run many applications if we didn't have enough physical RAM installed. As we know, the system itself is using a portion of RAM. If we run more applications, each application will also get its own portion of RAM. If we run too many applications, at one point we will run out of RAM. At that point we won't be able to open any additional application. Back in those days
3 Input And Output Devices
3.1 In computing, input/output or I/O (or informally, io or IO) is the communication between an information processing system (such as a computer) and the outside world, possibly a human or another information processing system. Inputs are the signals or data received by the system and outputs are the signals or data sent from it. The term can also be used as part of an action; to "perform I/O" is to perform an input or output operation. I/O devices are used by a human (or other system) to communicate with a computer. For instance, a keyboard or mouse is an input device for a computer, while monitors and printers are output devices. Devices for communication between computers, such as modems and network cards, typically perform both input and output operations.
4 The CPU
4.1 Fetch: Fetches a instruction from cpu
4.2 Decode: Decodes The Instruction
4.3 Execute:Executes the instruction
4.4 A computer's CPU is considered the "brain of the computer," being responsible for its major processes, like searching for information, sorting information, making calculations and advanced processes as well as decisions integral to the functioning of the computer. The acronym CPU actually stands for central processing unit and, as such, works behind virtually any task the user is doing on their computer, like writing essays, making photo albums or reading emails
4.5 CPU clock speed, or clock rate, is measured in Hertz — generally in gigahertz, or GHz. A CPU's clock speed rate is a measure of how many clock cycles a CPU can perform per second. For example, a CPU with a clock rate of 1.8 GHz can perform 1,800,000,000 clock cycles per second.
4.6 A CPU cache is a cache used by the central processing unit (CPU) of a computer to reduce the average time to access data from the main memory. The cache is a smaller, faster memory which stores copies of the data from frequently used main memory locations. Most CPUs have different independent caches, including instruction and data caches, where the data cache is usually organized as a hierarchy of more cache levels

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