Central Processing Unit Part I

1. Central Processing UnitPart I Bayram Güzer

2. Central Processing Unit • Central processing unit is a control center that converts data input to information output. • It includes complex set of electronic circuit components. • It executes stored program instructions • Central processing unit consist of two main parts; • Control unit • Arithmetic logic unit

3. Central Processing Unit • CPU interacts closely with memory (primary storage). • Memory often regarded in the context of the central processing unit however it is not part of the CPU, it is a seperate piece of unit.

4. Central Processing Unit • Memory holds the data temporarily at the time the computer is executing a program. • Secondary storage holds permanent or semipermanent data on some external medium until it is needed for processing.

5. Control Unit • The control unit contains circuit components that uses electrical signals to direct the entire computer system to execute stored program instructions. • Like the orchestra leader • It doesn’t execute program instructions but it directs other parts of the system to do so. • It communicates with both arithmetic/logic unit (ALU) and memory.

6. Arithmetic/Logic Unit (ALU) • The ALU contains the electronic circuit components that executes all arithmetic and logical operations. • ALU performs four kinds of arithmetic operations; • Addition • Subtraction • Multiplication • Division

7. Arithmetic/Logic Unit (ALU) • Logical operation is usually a comparison. The unit can compare; • Numbers • Letters • Special characters • Logical operations can test three conditions • Equal to, less than and greater than condition.

8. Arithmetic/Logic Unit (ALU) • Equal-to condition • Compares two values to determine if they are equal • Less-than condition • Compares two values to determine if one is less than another • Greater-than condition • Compares two values to determine if one is greater than another.

9. Arithmetic/Logic Unit (ALU) • Combined conditions • Less-than or equal to • Checks to find if one value is less than or equal to the other value. • Greater-than or equal to • Checks to find if one value is greater than or equal to the other value • Not equal to (literally sometimes referred as greater than or less than) • Checks to find if one value is not equal to the other value

10. Arithmetic/Logic Unit (ALU) • Relational operators are the symbols which lets you define the type of comparison you want the computer to perform

11. Registers • Registers are special-purpose, high-speed, temporary storage areas for instructions of data. • Not part of memory • Special additional storage locations • High-speed access is available • Registers work under the direction of the control unit • To accept, hold, and transfer instructions or data • To Keep track of where the next instruction to be executed or needed data is stored

12. Registers • Some of the register types are; • Address register: keep track of where a given instruction or piece of data is stored in memory. • Storage register: temporary holds data taken from or about to be sent to memory. • Accumulator: collects the results of computations. • There are other types of registers which is used for several functions as well.

13. Memory • It is also known as primary storage and main memory • Often expressed as random-access memory (RAM) • Not part of the CPU • Memory stores program instructions or data as long as it is in the operation and has not been terminated. • The CPU cannot process data from an input device or disk directly, therefore the data must first be available in memory. • Control unit is responsible from; • Receiving the items from memory • Sending the items from memory • Transferring the items from memory to secondary storage.

14. Memory • It is also known as primary storage and main memory • Often expressed as random-access memory (RAM) • Not part of the CPU • Memory stores program instructions or data as long as it is in the operation and has not been terminated. • The CPU cannot process data from an input device or disk directly, therefore the data must first be available in memory.

15. How the CPU Executes Instructions • Before an instruction can be executed, program instructions and data must be placed into memory from an input device or a secondary storage. Control Unit ALU 3 2 Decode Execute 1 Fetch 4 I-Time E-Time Store Memory

16. How the CPU Executes Instructions • Instruction has been executed in 4 different steps; • Fetch • Decode • Execute • Store Control Unit ALU 3 2 Decode Execute 1 Fetch 4 I-Time E-Time Store Memory

17. How the CPU Executes Instructions • Fetch: The control unit gets the instruction from the memory • Decode: The control unit decodes the instruction and directs the necessary data to be moved from memory to the ALU. • The first two steps are together are called as instruction time (I-time) Control Unit ALU 3 2 Decode Execute 1 Fetch 4 I-Time E-Time Store Memory

18. How the CPU Executes Instructions • Execute: The arithmetic logic unit executes the arithmetic or logical instructions by performing the actual operations on real data. • Store: The arithmetic logic unit stores the result of this operation in memory or in a register. • Step 3 and 4 together are called as execution time (E-time). • The combination of I-time and E-time is called as machine cycle. Control Unit ALU 3 2 Decode Execute 1 Fetch 4 I-Time E-Time Store Memory

19. How the CPU Executes Instructions • Each central processing unit has an internal clock that produces pulses at a fixed rate to synchronize all computer operations. • Pulses are electronic signals like heart beat, clock beat, or school ring. Control Unit ALU 3 2 Decode Execute 1 Fetch 4 I-Time E-Time Store Memory

20. How the CPU Executes Instructions • Clock pulse has two stage; • high voltage (like a tick sound) - ON • Low voltage (like a tock sound) - OFF • Clock tells circuits when to start sending data on wires and when not to sent data on wires. Control Unit ALU 3 2 Decode Execute 1 Fetch 4 I-Time E-Time Store Memory

21. How the CPU Executes Instructions • Instruction set is a specific group of instructions which each type of CPU is designed to understand. Control Unit ALU 3 2 Decode Execute 1 Fetch 4 I-Time E-Time Store Memory

22. How the CPU Executes Instructions • SET TOTAL TO 0 • ADD NEXT NUMBER TO TOTAL DATA:88 • ADD NEXT NUMBER TO TOTAL DATA: 76

23. How the CPU Executes Instructions • Fetch: fetch the instruction from the memory • Decode: control unit determines that addition must take place and gives instructions for the next number • Execute: ALU does the addition, increasing the total to 164 • Store: ALU stores the new total in the register and removes old value in the register.

24. How Control Unit Finds Instructions and Data • Each memory location has identified by an address • A unique number, much like a mailbox • Each memory location may contain only one instruction or piece of data • When data is written back to memory, previous contents of that address are destroyed • Each address is referred to by number but • Programming languages use a symbolic (named) address, such as Hours or Salary

25. References • Capron, H. L. (2000). Computers Tools for an Information Age.(6th ed.). New Jersey, USA: Prentice Hall. • http://homepage.cs.uri.edu/faculty/wolfe/book/Readings/Reading04.htm • http://en.wikipedia.org/wiki/Pulse_%28signal_processing%29 • http://www.yale.edu/pclt/PCHW/clockidea.htm • http://www.camiresearch.com/Data_Com_Basics/data_com_tutorial.html • http://en.wikipedia.org/w/index.php?title=Relational_operator