Pope Paul VI College Information and Communication Technology

Transcription

1 Pope Paul VI College Information and Communication Technology CPU - Central processing unit (CPU) is the brain of a computer which and instructions of a computer program. - It executes computer instructions such as addition, subtraction, multiplication, division and between two numbers. - It controls overall operations of every part of the computer - It contains a small amount of fast storages, called as, which hold the instructions and data during data processing - IT consists of two major components: and. Main Memory - Main is the cells accessible to the CPU. Each of these cells has its own unique and information. The information stored in the cell can be or. - There are two types of : and - All information from input devices or secondary storage device (for example, hard disk) has to be stored in first before being executed by the CPU Secondary Storage Device Secondary Storage Device is a type of storage There are a few types of secondary storage devices: hard disk, optical disc, card, solid-state disk (SSD) Data flow between CPU, Main Memory and Secondary Storage Device To perform data processing, there are several data flow of transfer:. Data are copied from to. Data are stored in temporarily. CPU fetches the data in for execution and interpretation. gets the resulting data for data storage 5. The resulting data are copied from to

2 Performance of CPU The performance depends on the following factors:. System Clock Rate - System clock is a small chip that synchronizes or controls the timing of all computer operations. - It generates regular ticks that set the operating pace of the hardware in the system unit. - CPU requires several clock cycles to execute each instruction. - Its unit is Hertz (Hz) and it is usually measured in GHz nowadays. - A higher clock rate means the CPU can process more instructions per second.. Word Length (Word Size) - Word Length is the number of bits that the CPU can manipulate at one time. - A CPU with a higher word size can handle more data with each operation and therefore has higher performance.. Cache Memory - Cache is a fast type of Random Access () that CPU can access more quickly than usual Main Memory. - CPU searches the required data in the cache before fetching from the main - It is used to store frequently used data Register Both and the contains registers, which are fast storage locations that temporarily hold data and instructions during processing. Their capacities are usually very low (around a few bytes). Comparing the transfer speed, Register > cache > main > secondary storage device Comparing the storage capacity, Register < cache < main < secondary storage device The functions of some common registers are introduced in the following: Accumulator (AX) - Store the addition result or temporary result in the Status register (SR) - Assists calculation by storing the state of the program execution Instruction register - Store the instruction in use for execution Program counter() - Stores the of the instruction to be executed Memory register () - Stores the of the contents to be fetched or stored Memory data register () - The content in is sent to/from the through the data buses

3 Instruction and machine cycle An instruction contains two parts, operation code and operand Operation code = to be done Operand = to be executed by the op code Instruction: Op code Operand Example: Load Memory 00 to register AX ADD Add Memory to register AX When a computer executes an instruction, it will process a single cycle called machine cycle. Machine cycle of a CPU with different sub-cycle Sub-cycle Description Example. Fetch Obtaining a program instruction from LOAD the instruction 98. Decode Translating the instruction (by fetching the 98 data) into commands the computer understand. Execute Carry out the commands 98 =08. Store Writing the result of 08 System bus System bus is a physical wiring connecting different parts within a computer system. Three main types of wires or lines contained in a bus: Data bus: carry data signals. Address bus: carry signals to specify the to be processed. Control bus: carry signals that control the start and end of the data transfer. More to learn Bus speed also affects a computer s performance. Bus flow of various units of a computer It is defined by the number of data packers send or received per second and the unit is Megahertz (MHz)

4 Using the instruction and ADD as an example. Step Fetching Instruction Instruction decoder ACMULATOR (AX) Load the content of 00 into register AX 6 5 Which of the above numbers belongs to the fetch sub-cycle? Which of the above numbers belongs to the decode sub-cycle? Step Fetching data from ACMULATOR (AX) What kind of sub-cycle does number belongs to? (Fetch / Decode )

5 SR Step Fetching Instruction ADD Instruction decoder 000 ACMULATOR (AX) 6 ADD 5 Step Fetching data from and execute the instruction 000 ACMULATOR (AX) ADD Complete all the missing information above.