Unit 3

(Hardware)

VON NEUMANN ARCHITECTURE [2018, 2019]

1. Von Neumann architecture was first published by John von Neumann in 1945.
2. His computer architecture design consists of a Control Unit, Arithmetic and Logic Unit (ALU), Memory Unit, Registers and Inputs/Outputs.
3. Von Neumann architecture is based on the stored-program computer concept, where instruction data and program data are stored in the same memory.
4. This design is still used in most computers produced today.

Explain what is meant by the stored program concept? [2019/2021]

Programs/Instructions and data stored in the same/main memory
Instructions fetched and executed in order / one after another / in sequence

Central Processing Unit (CPU)

1. The Central Processing Unit (CPU) is the electronic circuit responsible for executing the instructions of a computer program.
2. It is sometimes referred to as the microprocessor or processor.
3. The CPU contains the ALU, CU, and a variety of registers.

Registers [Name three Registers (2020)]

Registers are high-speed storage areas in the CPU. All data must be stored in a register before it can be processed.

1. MAR (Memory Address Register)- Holds the memory location of data that needs to be accessed [2019]
2. MDR (Memory Data Register)-Holds data that is being transferred to or from memory
3. AC (Accumulator)- Where intermediate arithmetic and logic results are stored, this register is built into the arithmetic logic unit (ALU).
4. PC (Program Counter)- Contains the address of the next instruction to be executed [2019]
5. CIR (Current Instruction Register)- Contains the current instruction during processing
6. Immediate access store (IAS)- Holds data and instructions when they are loaded from main memory and are waiting to be processed.

Arithmetic and Logic Unit (ALU) [2019]

The ALU allows arithmetic (add, subtract, etc) and logic (AND, OR, NOT etc) operations to be carried out.

Control Unit (CU)

The control unit controls the operation of the computer’s ALU, memory and input/output devices, telling them how to respond to the program instructions it has just read and interpreted from the memory unit.
The control unit also provides the timing and control signals required by other computer components.
Responsible for decoding instructions. [2020]

Buses [2017, 2020]

Buses are the means by which data is transmitted from one part of a computer to another, connecting all major internal components to the CPU and memory.

A standard CPU system bus is comprised of a control bus, data bus and address bus.

Address Bus (Unidirectional) Carries the addresses of data (but not the data) between the processor and memory
Data Bus (Bi-directional) Carries data between the processor, the memory unit and the input/output devices
Control Bus (Unidirectional/Bi-directional) Carries control signals/commands from the CPU (and status signals from other devices) in order to control and coordinate all the activities within the computer

Memory Unit

The memory unit consists of RAM, sometimes referred to as primary or main memory. Unlike a hard drive (secondary memory), this memory is fast and also directly accessible by the CPU.
RAM is split into partitions. Each partition consists of an address and its contents (both in binary form).
The address will uniquely identify every location in the memory.
Loading data from permanent memory (hard drive), into the faster and directly accessible temporary memory (RAM), allows the CPU to operate much quicker.

Identify some components that are part of the CPU. [2020]

− MAR

− MDR

− PC

− ALU

− CU

− ACC

− CIR

− Buses

− Registers

FETCH-DECODE-EXECUTE CYCLE

The PC (Program counter) contains the address of the memory location of the next instruction which has to be fetched
This address is then copied from the PC to the MAR (Memory address Register)
The contents (instruction) at the memory location (address) contained in MAR are then copied temporarily into the MDR (Memory Data Register)
The contents (instruction) of the MDR are then copied and placed into the CIR (Current Instruction Register)
The value in the PC is then incremented by 1 so that it now points to the next instruction which has to be fetched
The instruction is finally decoded and then executed by sending out signals (via the control bus) to the various components of the computer system

The CPU is responsible for processing instructions which are: FETCH, DECODE and EXECUTE [2020]

VIDEO LESSONS (Source: Youtube)

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