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Computer Studies Computer Memory and Data Transfer.

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Presentation on theme: "Computer Studies Computer Memory and Data Transfer."— Presentation transcript:

1 Computer Studies Computer Memory and Data Transfer

2 Computer Studies Hardware A General Overview –What is a computer? A computer is a machine that processes data and produces information. –How does it function? Before it can do anything, programs must be installed to give the computer the instructions on how to process the information. This is done using an input device. –What happens then? When the computer is finished processing, it produces results. This is shown through an output device.

3 Computer Hardware Backing Storage CPU Central Memory INPUT OUTPUT

4 Computer Studies Hardware - The Basics

5 Computer Studies Organisation of Data The main memory of a computer is used to store programs and data. The memory size is measured in kilobytes, megabytes, or gigabytes. KILOBYTE1024 bytes MEGABYTE1024 x 1024 bytes GIGABYTES1024 x 1024 x 1024 bytes Different types of Memory ROMOnce programmed it cannot be erased EPROMCan be erased by exposure to UV light. EAPROMCan be partially programmed or flashed which changes the original coding.

6 Computer Studies Organisation of Data Data is organised in a number of different units of storage. BITthe smallest unit of storage can store a 0 or 1 BYTEa collection of 8 bits NIBBLEa group of 4 bits or half the length of a byte WORDa group of bits stored by the computer as a single unit – usually multiples of 8 bits. A 16 bit computer will work with words 16 bits long. Most modern computers will work with words 32 bits long or higher.

7 Computer Studies Hardware – data organisation Word Length –A group of bits that can be transferred and manipulated as a single unit by the CPU. –The amount of bits the CPU can send or receive at once. An 8 bit CPU will send or receive 8 bits of data. A 16 bit CPU will send or receive 16 bits of data. –A computer with an 800 mhtz which has a word length of 2 bytes (16 bit) is twice as fast as the same processor with 8 bit data transfer rate so it performs functions in half the time.

8 Computer Studies Hardware The Data and Address Bus - A series of copper strips that act as highways along which data travels between the CPU, Memory, and peripherals. Anything that requires the transfer of data is connected to the bus. It is the method by which information moves across the computer system: –Data Bus: –Its width determines the amount of information that can be transferred. –Address Bus: –Travels with the data along the bus.

9 Computer Studies Hardware – General Overview The Data and Address Bus act like a letter. The address part is the envelope, and the data section consists of the letter. The address bus helps the computer find the correct location – and deliver the information inside the envelope. They travel together.

10 Computer Studies The Basic Computer Central Memory - Made up of two main parts: –Random Access Memory –Read Only Memory RAM It is the working desk of the computer. Programs run in RAM. Used for temporary storage of Data and programs. It is volatile – information is lost when power is lost. Because of this backing storage is needed. WHAT DOES RAM DO?

11 Computer Studies The Basic Computer Central Memory - Made up of two main parts: –Random Access Memory –Read Only Memory ROM Stores data required permanently. Programs run in RAM. Instructions are normally encoded during the manufacture of the chip. The contents cannot be changed. Because of this backing the Rom normally contains the booting instructions needed to start the computer. WHAT DOES ROM DO?

12 Computer Studies The Basic Computer Storage Backing Storage Much higher Capacity than RAM or ROM. Stores data for a permanent period. Different forms such as: Hard Disks Magnetic Tape Floppy Disks CD Roms. WHAT DOES BACKING STORAGE DO?

13 Computer Studies Machine Code - –The CPU only understands machine code – binary digits – a series of 0s and 1s. –An instruction set is a group of instructions understood by the CPU. –Different generations of CPUs have their own instruction sets. Assembly Language –A separate programming language called assembly language was created which is easier to understand. –These are called low level languages. –Programmers need to learn these languages before they can program a computer. –Uses abbreviated words to give the computer commands - Mnemonics Hardware – The CPU

14 Computer Studies Hardware - The CPU CPU - Made up of two main parts: –Arithmetic Logic Unit –Control Unit ALU Performs mathematical calculations CU Manages and controls all movements to and from all peripherals to the CPU

15 Computer Studies Hardware - Speed The CPU Speed –Depends on the internal clock of the CPU? Sometimes referred to as clock speed Measured in MHz or MIPS (millions of instructions per second). –Hertzis one cycle per second –MHzis one million cycles per second (megahertz) –MIPsare millions of instructions per second –Todays computers operate at millions of cycles per second (e.g.. Pentium IV – 266) There are other factors that effect the computers speed.

16 Computer Studies Hardware - Speed The Cache –A type of very fast Memory It can be part of the CPU or it can be external – e.g.. Placed on the motherboard near the CPU. Used to carry out calculations and repetitive actions. These are then passed back to the CPU. Cache allows the CPU to perform other functions at the same time. Different sizes of cache: 128k, 256k, 512k.

17 Computer Studies Hardware - The CPU Control Unit - The manager of the computer. Its primary functions are: –Carry out the instructions stored in memory –Contains the –Instruction register –Stores a copy of the current instruction that is being processed. –Program counter –Stores the location of the next instruction to be executed.

18 Computer Studies Hardware Arithmetic Unit - Two main sections: –The Accumulator: –Stores the current results of a calculation –The Shift Register: –Moves its contents one or more positions to the right or left in order to carry out arithmetic operations.

19 Computer Studies Hardware – The CPU Arithmetic Unit - The calculator of the computer. Its primary functions are: –Carries out the instructions that require mathematical calculations –Carries out Mathematical Functions: –Addition, Subtraction, Multiplication and Division –Greater than>, Less than<, Equal to= –Greater than or equal to>=, Less than or equal to<=, –Not equal to<>, –The three logical Functions: –NOT –AND –OR

20 Hardware Block Diagram

21 Computer Studies Fetch Execute Cycle –A) Set the value of the program to the address of the 1 st instruction. –B) Fetch the instruction from the location specified by the program counter. –C) Store a copy of this instruction in the instruction register. –D) Increment the program counter by 1. –E) EXECUTE the instruction: –Fetch any data required by the instruction –Place it in storage locations within the ALU called Data Registers. –Activate the correct circuits for the instruction to be carried out. –Move any results from the data registers back to main memory. –F) Repeat process from step B.

22 Computer Studies The Fetch / Execute Cycle

23 Computer Studies Sample Machine / Assembly (Programming) Code 0000ENDStop the Execution of a program 0001ADDAdd the contents of the memory location to the accumulator. 0010SUBSubtract the contents of the memory location to the accumulator 0011MULTMultiply the contents of the ML to the accumulator 0100DIVDivide the contents of the ML into the accumulator 0101LDACopy the contents of the ML into the accumulator 0110STOCopy the contents of the Accumulator to the ML 0111INInput from Input Unit to the ML 1000OUTOutput Contents of the ML to the Output Unit 1001JMPTransfer control to the Instruction in a Named Location. 1010JNZJump (skip) if contents of the accumulator is not zero

24 Computer Studies A simple program to add two numbers input from the keyboard 100INAccept a number from the KB and store it in ML INAccept a number from the KB and store it in ML LDALoad the number stored in ML 100 in to the accumulator 101ADDAdd the number stored in ML 101 into the accumulator 102STOStore the value currently in the accumulator into ML OUTOutput the value stored in ML 102 into an output device

25 Computer Studies A simple program to add two numbers input from the keyboard 100INAccept a number from the KB and store it in ML INAccept a number from the KB and store it in ML LDALoad the number stored in ML 100 in to the accumulator 101ADDAdd the number stored in ML 101 into the accumulator 102STOStore the value currently in the accumulator into ML OUTOutput the value stored in ML 102 into an output device

26 Peripherals –Input and Output devices The computer receives instructions from the input peripherals. Displays results on the output peripherals. Holds information on secondary storage peripherals. Computer Studies

27 Peripherals –Input Devices Keyboard Mouse Light Pen Digital Camera Digitizing Tablet Bar Code Reader Computer Studies

28 Peripherals –Input Devices Speech Reader Magnetic Ink Character Reader Hand Held Terminal Touch Screen Optical Character Reader (OCR) Scanner Computer Studies

29 Output Peripherals Soft copy- Visual (monitor) or spoken (speakers) Hard copy – computer output on a tangible medium such as paper


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