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Level 66

Von Neumann Architecture & the CPU


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Von Neuemann architecture
It is based on the idea that data and the program processing them should be stored in the same memory. Effectively the program itself is treated as data.
Turing Test
It's still used today to decide if a computer has fooled a person into thinking they are conversing with another person rather than a computer.
Essential features of the Von Neuemann architecture
ALU (Arithmetic Logic unit), CU (Control Unit), Memory, I/O (input/output), Bus.
Memory
a component on the motherboard that stores data electronically
Control Unit
It manages the process of moving data and program into and out of memory and also deal with carrying out (executing) program instructions - one at a time.
Input/output (I/O)
Controllers that are used by the CPU to communicate with peripherals e.g. mouse and keyboard. Whatever values that are passed to and forth are stored once again in some internal registers.
Arithmetic Logic Unit (ALU)
This part of the architecture is solely involved with carrying out calculations upon the data. It consists of two parts: the Arithmetic part which performs the calculations on the data (Add, Multiply, Divide and Subtra…
Buses
They are the "arrows" between components and thanks them information could flow between various parts of the computer.
data bus
it's a hardware path where data travel from main memory into the CPU.
address bus
a vital hardware path made by the CPU which places the address of the next item to be fetched on to the address bus.
register
It is a discrete memory location within the CPU designed to hold temporary data and instructions.
Program counter (PC)
it's a register that hold the address in memory of the next instruction.
Current Instruction Register (CIR)
It's holds the current instruction to be executed, having been fetched from memory.
Program Status Word (PSW)
It can contain the result of a comparison dona by ALU, it indicates IF statements and it also holds error flags.
IF statements
it allows execution to jump from one set of instructions to another.
Flag
It denotes a single binary bit within a register (PSW). They are often used to indicate a true or false condition.
Error flag
it indicates a number of problems that may have happened as a result of an instruction.
Memory Address Register (MAR)
It holds the location in memory (address) of the next piece of data or program to be fetched.
Memory Buffer Register or Memory Data Register
It temporarily holds the data or program instruction which is fetched from memory.
buffer
It is a commonly used computer term to describe memory designed to hold data that is on its way to somewhere else.
fetch-decode-exectue cyIcle
A standard process describes the steps needed for processing to take place. It uses registers to move data and instructions around the CPU.
Von Neumann bottleneck
It's a problem caused by the data bus which is a lot slower than the rate at which the CPU can carry out instructions. If nothing were done, the CPU would spend most of…
Cache
In web terms: A web browser or web server feature which stores copies of web pages on a computer's hard disk.
code optimisation
It's the activity of the software programmer to make easier for the CPU to store the most-often used part of the code in the 'cache'.
Problem connected with sharing memory space
It is quite easy for a poorly written or faulty piece of code to write data into an area holding other instructions, so trashing that program.
Problem connected with speed
The rate at which data needs to be fetched and the rate at which instructions need to be fetched are often very different. And yet they share the same bottlenecked data bus.
Harvard Architecture
The idea is to split the memory into two parts. One part for data and another part for programs. Each part is accessed with a different bus. This means the CPU can be fetching …
CPU
acronym for central processing unit, where all the PCs calculations take place
the purpose of the CPU
It's to process data. It is where all the searching, sorting, calculating and decision making takes place in the computer.
fetch, decode, execute
Step of the CPU
fetch
During which phase of the instruction execution cycle is the program counter incremented?
DECODE
The second step of the CPU is to make sense of the instruction it has just fetched. The CPU decodes the instruction and prepares various areas within the chip in readiness of the next step.
instruction set
a specific set of commands that CPU is designed to understand. Each make of CPU has a different instruction set.
Execute
Process of a computer carrying out the instructions in a program.
The Immediate Access Store
It holds the data and programs needed at that instant by the Control Unit.
IAS's memory
It's where the CPU temporarily stores the data and programs just read (kept on the banking storage).
clock
It's inside the CPU and it controls the amount of time that CPU has to process each piece of data. With every tick of the clock, the CPU is able to process one piec…
CPU clock Speed
It's measured in cycles per second. 1 cycle per second is also known as 1 Hertz. Naturally the speed of the clock determines the basic performance of the CPU - the faster it goes, the more powerful the computer.
Clock speed higher
faster performance but runs hotter and consumes more power.
Clock speed lower
lower performance, less costly, needs less power - so good for battery life in laptops.
Overclocking
Some people try to get the most extreme performance out of their existing CPU adjusting the clock to run faster than the CPU was really designed for.
Cpu cores
Extra CPU that you can add to improve the performance. A modern processing device may contain two or even four CPUs.
Volatile Memory
Memory that requires power to retain the stored information