Central Processing Unit Part I Bayram Güzer

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 2

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. 3

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. 4

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. 5

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 6

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. 7

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. 8

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 9

Arithmetic/Logic Unit (ALU) Relational operators are the symbols which lets you define the type of comparison you want the computer to perform ExplanationC-likeBASIC-like Equal to=== Not equal to!= Greater than>> Less than<< Greater than or equal to>= Less than or equal to<= C-like: C, C++, C#, Java, Perl, PHP, Javascript Basic-like: Basic, Pascal, SQL. 10

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 11

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. 12

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. 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. 14

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. Memory Control UnitALU Fetch DecodeExecute Store I-TimeE-Time 15

How the CPU Executes Instructions Instruction has been executed in 4 different steps; –Fetch –Decode –Execute –Store Memory Control UnitALU Fetch DecodeExecute Store I-TimeE-Time 16

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) Memory Control UnitALU Fetch DecodeExecute Store I-TimeE-Time 17

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. Memory Control UnitALU Fetch DecodeExecute Store I-TimeE-Time 18

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. Memory Control UnitALU Fetch DecodeExecute Store I-TimeE-Time 19

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. Memory Control UnitALU Fetch DecodeExecute Store I-TimeE-Time 20

How the CPU Executes Instructions Instruction set is a specific group of instructions which each type of CPU is designed to understand. Memory Control UnitALU Fetch DecodeExecute Store I-TimeE-Time 21

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

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. 23

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 24

References Capron, H. L. (2000). Computers Tools for an Information Age.(6th ed.). New Jersey, USA: Prentice Hall. ings/Reading04.htm ssing% ta_com_tutorial.html _operator 25