Computer Architecture

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Introduction to computer architecture : 

Introduction to computer architecture By Clodagh Brennan 20046596, Lorcan O Concubhair 20046053and Emma Fitzpatrick 20046421

The Central processing Unit : 

The Central processing Unit Foundations of Computing

The CPU : 

The CPU The Central Processing Unit is the “brain” of the computer without this there is no computer. CPUs are so small that sometimes they are referred to as microprocessors. The CPU is composed of a control unit, an arithmetic and logic unit, registers, a clock and wires which connect everything together..

Arithmetic-logic Unit : 

Arithmetic-logic Unit The arithmetic-logic unit performs all the arithmetic operations such as addition and subtraction and logic operations such as AND. Logic operations test different conditions in a process and allow for different actions to be taken according to the result. The Arithmetic Logic Unit has three sections the registry, the ALU circuitry and the pathways between.

Control Unit : 

Control Unit The control unit is the circuitry that controls the flow of information entering and leaving the computer. It maintains order throughout the system and directs the flow of the operations. The control unit fetches from memory the next program to be run, then it decodes what needs to be done and then it issues the command to the ALU, memory and I/O controllers so the job will be done. The control unit controls what happens inside the processer.

Clock : 

Clock The clock is a circuit in the processor which generates a sequence of electronic pulses which synchronise the operations of the processors components. The execution times of instructions are measured by number of clock cycles rather than seconds.

Registers : 

Registers Registers are temporary storage units within the CPU. Different registers store different things and some registers like storage, interpretation and execution of instructions and the intermediate results are for exclusive use for the CPU.

Von Neumann Architecture : 

Von Neumann Architecture Foundations of Computing

The Architecture : 

The Architecture A von Neumann Architecture computer has five parts:  an arithmetic-logic unit, a control unit, a memory, some form of input/output and a bus that provides a data path between these parts. Virtually every electronic computer ever built has ties to this architecture.

Northbridge Southbridge chipset : 

Northbridge Southbridge chipset The function of a chipset is to communicate between the components of a modern computer. Chipsets are made up of a number of integrated circuits designed to perform one or more related functions. Each part of the chipset (Northbridge or Southbridge) has its own tasks and specific functions.

Northbridge Chipset : 

Northbridge Chipset The Northbridge coordinates high bandwidth pathways. Northbridge determines the amount, type and CPU speed that can be attached to the motherboard. The Northbridge interacts with the computer processor and memory.

Northbridge Chipset : 

Northbridge Chipset The Northbridge is the high speed part of chipset architecture in a computer. The Northbridge connects the CPU to: RAM AGB Bus PCI Express Built-in display adapter

Southbridge Chipset : 

Southbridge Chipset Southbridge is a chipset that manages the basic forms of input/output. Slower I/O traffic is handled by the Southbridge.

Southbridge chipset : 

Southbridge chipset The Southbridge connects the CPU to: ATA (IDE) Drives USB bus FireWire bus Serial port Parallel port Built-in audio ISA bus (earlier PCs)

The Fetch and execute Cycle : 

The Fetch and execute Cycle Foundations of Computing

Fetch-Execute Cycle : 

Fetch-Execute Cycle First proposed by John von Neumann. (1998-06-25)

The fetch : 

The fetch The operation of the fetch is when information is obtained from the main memory. The registers are a sequence of steps that happens when the CPU (Central Processing Unit) fetches an instruction from the memory. It involves several registers inside the CPU - specifically, the Program Counter. When the next instruction is to be fetched, this register is incremented by the appropriate number of bytes.

THE Execution : 

THE Execution When a computer obeys the instructions in a computer program it is executing the program. Before a computer can execute a computer program the program must be resident in memory. The program must occupy a set of consecutive bytes in memory and must be written in the internal machine language for the computer. .

connection : 

connection At the beginning of each cycle the CPU presents the value of the program counter on the address bus. The CPU then fetches the instruction from main memory via the data bus into the instruction register. From the instruction register, the data forming the instruction is decoded and passed to the control unit which sends a sequence of control signals to the relevant function units of the CPU to perform the actions required by the instruction such as reading values from registers, passing them to the ALU to add them together and writing the result back to a register. The program counter is then incremented to address the next instruction and the cycle is repeated.

Slide 21: 

The instruction LDA #7 in the 6502 assembly language means "Load the accumulator with the value 7." The sequence of instructions is now as follows: The CPU fetches the instruction "LDA with the following value" The CPU is programmed so that when it received this instruction, it fetches the next byte from memory. This is done by increasing the memory address register by 1 (the next byte on from the instruction) - or using the program counter if the CPU doesn't have a memory address register - and fetching the next byte as per normal. The value read in (7 in this case) is placed into the accumulator (A), thus replacing any value that was already in there. The status flags are changed accordingly. Because the value was not 0, the zero flag is cleared.

Thank you : 

Thank you By Emma Fitzpatrick 20046421, Lorcan O Concubhair 20046053 and Clodagh Brennan 20046596

References : 

References Norton Riley H. (1987). The von Neumann Architecture of Computer Systems. Available at: (Accessed: 14/12/10) Velocity Guide. John von Neumann (1903-1957). Available at: (Accessed: 14/12/10) Risley D. (2001) Von Neumann Architecture. Available at: (Accessed at: 14/12/10) Information Technician. Arithmetic-Logic Unit. Available at: (Accessed at: 14/12/10) Nbridge –Sbridge.JPG. Available at: (Accessed at: 14/12/10)

References : 

References Webopedia. What is Chipset? Available at: (Accessed at: 14/12/10) PC Mag. Northbridge Definition. Available at:,2542,t=Northbridge&i=48076,00.asp (Accessed at 14/12/10) Basic Science Blog. Basic Computer Science: Computer Chipsets. Available at: (Accessed at 14/12/10) Whatis. Southbridge. Available at: ht tp://,,sid9_gci750982,00.html (Accessed at 14/12/10)

references : 

references InetDaemon. Central Processing Unit. Available at: (Accessed at 14/12/10)

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