The cpu cycle

by Jeanne Ndatirwa

1. Reusable learning object on the CPU cycle BY Jeanne Ndatirwa March 24 th , 2013

2. Introduction The CPU which is often described as the “brain of the computer ”. Most CPUs are collections of digital circuits imprinted on silicon wafers, or chips, no bigger than the tip of a pencil eraser. The increased speed the current in a CPUS travels at, can be increased by reducing the distance between points which has resulted in ever smaller chips (see Moore’s Law). The CPU cycle is closely associated with primary storage also known as main memory.

3. Purpose of the CPU The job of the CPU is to execute programs A program is a list of unambiguous instructions designed to be followed mechanically by a computer . Once the CPU executes a program, it is stored in a computer’s main memory (RAM or random access memory). The CPU can also store information in memory by specifying the information to be stored and the address of the location where it is to be stored.

4. Hardware Components The CPU consists of three elements: The arithmetic/logic unit (ALU ): performs mathematical calculations and makes logical comparisons. The control unit : sequentially accesses program instructions, decodes them, and coordinates the flow of data in and out of the ALU. Registers (storage area ): are high-speed storage areas used to temporarily hold small units of program instructions and data immediately before, during, and after execution by the CPU.

5. Components in action Executing any machine-level instruction involves two phases: instruction and execution . The instruction phase consists of: Fetch instruction: the computer reads the next program instruction to be executed and any necessary data into the processor. Decode instruction: instruction is decoded and passed to the appropriate processor execution unit. The time it takes to perform the instruction phase is called the instruction time (I-time ).

6. Components in action The execution phase consists of Execute instruction: hardware element, freshly fed with an instruction and data, carries out the instruction. Store results: results are stored in registers The time it takes to complete the execution phase is called the execution time (E-time ).

7. Processing

8. Processing

9. Processing Various measures are used to gauge processing speed: Machine cycle time: measured by how many instructions are executed in one second, also measured in nanoseconds or picoseconds. Clock Speed: series of electronic pulses produced at a predetermined rate that affects machine cycle, measured in mega or gigahertz.

10. Processing Multiprocessing : involves the simultaneous execution of two or more instructions at the same time. Coprocessor: the part of the computer that speeds processing by executing specific types of instructions while the CPU works on another processing activity. Multicore Microprocessor: a processor that combines two or more independent processors into a single computer as they share the workload. Parallel Computing: simultaneous execution of the same task on multiple processors to obtain results faster. Grid Computing: use of a collection of computers , usually owned by multiple individuals or organizations to work in a coordinated manner to solve a common problem.

11. Memory characteristics and function Main memory provides the CPU with a working storage area for programs and data. Computer memory takes several forms: Random access memory (RAM): a form of memory in which instructions or data can be temporarily stored. Ready-only memory (ROM): a non-volatile form of memory. Cache memory: a type of high-speed memory that a processor can access more rapidly than main memory.

12. Knowledge Assessment

13. Credits http:// www.teach-ict.com/gcse_computing/ocr/212_computing_hardware/cpu/miniweb/pg2.htm http:// math.hws.edu/javanotes/c1/s1.html http:// www.teach-ict.com/gcse_computing/ocr/212_computing_hardware/cpu/quiz/penalty_cpu.htm Stair, R. & Reynolds, G “Principles of information systems”, 10 th ed., pp. 91-97.