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Computer technology The history of computer technology video clip The history of computer technology video clip The history of computer technology video clip The history of computer technology video clip

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Low Level Machine

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how a computer handles the smallest amounts of data in its processor. Low Level Machine how data is represented inside the computer.

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Low Level Machine INPUT PROCESS OUTPUT

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Low Level Machine INPUTthe entering of the data. PROCESSthe calculation is done OUTPUT Random Access Memory stores the data by the central processing unit and the answer is the

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Low Level Machine The CPU consists of three parts: Memoryto store small amounts of instructions Arithmetic Logic Unitto do the calculations Control Unitcontrolling the input and outputs of the CPU

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Low Level Machine The CPU Memory ALU Control Unit Input line from keyboard Watch a video clip

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Low Level Machine The CPU Memory Arithmetic and Logic Unit Control Unit RAMRAM

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Low Level Machine 01010110 101010b1 01010101 01011 1000 10101110 1001i111 110101010 00010101 11111000 1n110000 11010 0101 10010101 1011011a 001110101 01010101 011011101 010r0101 0111 0101 01011101 11000111 1y100010 b i n a r y

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Binary is also known as machine code, as its the code which instructs the machine Every 0 or 1 is called a binary digit or bit Eight bits represent a character for example, 0100 0001 represents the letter A Eight bits together are called a byte We use the byte to measure capacity of a computers for example, kilobyte, megabyte and gigabyte.

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Low Level Machine Eight bits= 1 byte 1 kilobyte= 1024 bytes and is written as 1kb 1 megabyte= 1024*1024 kilobytes or = 1 048 576 bytes written as 1mb 1 gigabyte= 1024 * 1024 * 1024 kilobytes = 1 073 741 824 bytes or 1gb

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Low Level Machine If the computer has to process data it must store it All data is stored in the computers memory The memory of the computer is measured in bytes Each memory location can hold one byte of data (or a multiple of bytes) Each memory location has an unique address This way of identifying each memory location is called addressability

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Low Level Machine 01010011 11011011 memory locations 11011011 Each memory location will have its own unique address 00000001 00000010 00000011 00000100 00000101 00000110 00000111 00001000 00001001 00001010 00001011 00001100 00001101 00001111 memory addresses One byte

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Low Level Machine Data travels from input devices to the processor, or between RAM and the processor or to and from the different parts of the processor in groups of bits This group is called a WORD Older computers had a WORD LENGTH of 2 bits this increased to 4 and then 8 now most modern PCs have a WORD LENGTH of 16, 32 or 64 bits This means that data is passed around much faster and tasks carried more quickly

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Low Level Machine A 2 bit machine would transfer the data 2 bits at a time This would mean time for a total of 16 transfers A 8 bit machine would need only time for 4 transfers A 16 bit machine would need only time for 2 transfers A 32 bit machine would need only time for 1 transfer The data to be processed01011100 10101100

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Low Level Machine Doing a simple calculation (and not accurately reflecting) The 2 bit machine is 16 times slower than the 32 bit machine The data being processed will take 4 minutes on the 2 bit machine and only 15 seconds on a 32 bit

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Low Level Machine Each character that appears on the keyboard has a special code to represent it consisting of 1s and 0s these are known as alphanumeric characters Each country and language has a special collection of characters and so a collection of characters is known as a character set Computer manufactures have had to standardise on the binary code that they have allocated to each character and the most popular one is the ASCII set

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Low Level Machine AAmerican SStandard CCode IInformation IInterchange ASCII allows different Computer systems to communicate with each other because text is represented by the same code

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Low Level Machine Control Characters control certain operations the computer carries out For example ctrl-p will tell the operating system to print the current screen Other codes may tell the computer to print condensed or take a new line – the return key Control Characters are also represented by ASCII ASCII uses 7 bits and therefore one character set can have up to 127 individual characters

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Low Level Machine Graphics on the screen are made up of tiny dots called pixels The more pixels on the screen the better the picture The more pixels – the higher the resolution and the more memory needed to store each pixel In a black and white picture all black pixels would be stored as a 1 and all white pixels as a 0 So high resolution screens and graphics need more memory than low resolution ones

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Low Level Machine If we increase the size of this graphic we will begin to see the pixels Click here to see the graphic at 1000%

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Low Level Machine 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 Black pixels are represented by a 1 and white pixels by a 0

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Low Level Machine Binary can represent any number whole and real The binary number system is a base 2 system Decimal is a base 10 system 1286432168421 00000101 =5 01011010 =90 11111111 =255 01011000 = 88

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Low Level Machine Using binary to represent non negative integers is very straightforward Of course numbers larger than 255 will require more than 1 byte to represent them 4 bytes can be used to represent a number this gives the binary number 2 32 or thirty two 1s 11111111 11111111 This is 4,294,967,295 although the top of the range is about half of this to allow for negative numbers

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Low Level Machine But what happens when the number is bigger than 2000 million? The computer uses Floating Point Representation also known as standard form or scientific notation FPR is also used to represent real numbers i.e. numbers that are not whole numbers e.g. 51.6784, very small and and very large numbers. In decimal 60 420 000 000 can be represented as 6.042*10 10

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Low Level Machine Sign (+ or -) positive numbers are not signed Decimal FPR has four components: Exponent (10) Mantissa (6.042) Base (10) 6.042*10 10

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Low Level Machine The sign indicates whether the number is positive or negative The exponent indicates how many places the point has been moved The base indicates the number system being used The mantissa indicates how many places the point has been floated

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Low Level Machine In binary the position of the point is always the same The number base is always two All that is needed to be stored is the mantissa and the exponent 28.5= 11100.0101=0.111000101 * 0101 Decimal Binary FPR 1110001010101 MantissaExponent

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Low Level Machine Return to picture at 100% The pixels are the small squares

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