Fetch, execution and IO

•  The heart of the computer is the CPU which is also known as the Processor. It includes the arithmetic and logic and control in the system bus.
• Data is stored in bits. One byte is equivalent to eight bits.
• Computers interpret our intentions and process information by the representation of those instructions as bit.

Process of storing data

• User types a character.
• Keyboard converts the character into binary code.
• All the processing and storing are done in binary form.
• Transmission to the printer is in binary form.
• Printer converts binary code to characters before printing.

Functional units

• It is organized into words of typically 32 bits which contains 8-bit bytes.
• A personal computer memory might have 4 gigabytes or more.

Cache memory: It is an adjunct to the main memory which is smaller and faster. It holds the sections of data and program currently/frequently bring executed.

(Functional units) Processor:

• Logic circuits: for performing arithmetic and logic operations on word-size data operands.
• Timing and control circuits: for fetching program instructions and data from the memory.
• Registers: which hold one word of operand data sections of the program and data currently/frequently being executed.

Processor 

• Arithmetic and logic unit: Most computer operators are executed in ALU of the processor which performs arithmetic and logic operation.
• Control unit: Memory, ALU and I/O units store and process information and perform input and output operations.

Computer operation:

• Computer accepts information in a form of program and stores it in the memory.
• Information stored is fetched under program control into an ALU to be processed.
• Processed information leaves the computer through an output unit.
• All activities in the computer are directed by the control unit.

Instruction cycle: Derives its power by being able to repeat the basic operations. It is also known as single cycle of operation or machine cycle.

Consists of fetch, decode, execute, memory access and white back phases.

Instruction cycle operations:

1. Fetch the instructions.
2. Decode the instructions.
3. Execute the instructions.
4. If the instructions involve a memory operand, store the instructions.
5. Write the result into the designated register.

Instructions and programs: An instruction specifies an operation and locations of the data operands. A sequence of instructions constitutes a program. Both program and its data are stored in the main memory.

Three basic instruction types:

1. Load: Read a data operand from the memory.
2. Store: Write a data operand from a processor to memory.
3. Operate: Perform ALU operation on data operands in processor register.

Processor components:

1. The program counter/ PC register: Holds the memory address of the instructions.
2. The instruction register (IR): Holds the current instructions.
3. General purpose register: Holds data and address.
4. ALU: Fetch and executes the instruction.

Fetching and executing instructions:

The processor control circuits do the following:

• Send address in PC to memory.
• Load instructions from memory to IR.
• Increment PC to point to next instructions.
• Send address LOC to memory.
• Load word from memory into register R2.

PC: Program counter:

• The program counter increases by 1 when instructions get fetched.
• After the instructions are fetched, the program counter points to the next instruction.
• When the program counter restarts, the program counter normally reverts to 0.

Handling I/O Devices

1. Read data from an input device.
2. Write data to an output display screen.
3. Sense the readiness of an input or output device to perform a transfer.

Performance: how quickly can a program be executed:

1. Speed of electronic circuits in the processor.
2. Access time to the cache and the main memory.
3. Design of the instruction set.
4. Number of operations that can be done at the same time.

Technology: Improvement in process technology mean more transistors can be placed on a chip leading to:

• More logic functionality.
• More memory storage capacity.

Parallelism:

Multicore processors: Multiple processing units can be fabricated on a single chip where core is used for each of these processors. Dual-core, quad-core and octo-core processors are used for chips.