1.1

systems architecture

comprises of hardware and the way all different components connect together

hardware

the physical component of a computer system both internal and external

the 4 components of a computer system

the necessity of 4 components

All computer systems have:

• CPU

• a minimum of one input device that gathers data

• memory(primary storage) for program currently in use

• a store/to store data in secondary storage

CPU(Central Processing Unit)

A small piece of hardware that performs all the calculation/processing in a computer

• its main function is fetch-decode-execute

Transistors

Tiny switches that convert data into binary

• billions of them make up a CPU

• 0 = off, 1 = on

RAM(Random Access Memory)

Where currently running programs/data/operating systems are stored.

• All instructions need to be performed by the CPU are stored here

Stored Program Concept

Where program instructions/data are stored in the same memory(RAM)

• this means the memory doesn’t need to be repeatedly entered

• definition of Von Neumann Architecture

data vs program

• programs- instruction/algorithm CPU executes

• data- needs to be decoded in the CPU

Components of CPU

Internal Memory:

• General Purpose Registers(Including program counter)

The ALU(Arithmetic Logic Unit)

• arithmetic operations(+,-,*)

• logic operations(<,>,=)

• shift operations(moving data , sort of alignment?)

The CU(Control Unit)

• controls flow of data moving inside the CPU

• times signals to other units

• controls signals to direct operations within the CPU

Registers

a small amount of fast temporary memory within the processor where the ALU/CU can store & change values needed to execute instructions

Process in a register

program runs » stores value/calculations inside registers » small blocks of memory

• works like a variable

Program Counter

a special purpose register that holds the address(location number) of the next instruction to be executed.

• It’s located in the CU!

• incremented(goes up by 1) after fetching an instruction.

Accumulator(ACC)

Stores the results of arithmetic/logic operations

• speeds up process as data doesn’t have to be moved a further distance from main memory to CPU

MAR(memory address register)

holds the address of the current instruction being executed

MDR(memory data register)

stores:

• data fetched from memory

• data to be stored in memory

• data from MAR addresses

(ASF)

cache

memory built into CPU storing recently used instructions

• shortens distance when retrieving data instead of going to RAM to boost efficiency

relative distance of different cache memory

• L1- located on CPU(low capacity, same speed as cpu)

• L2- part of CPU module( a bit larger and runs at relatively same speed)

• L3- on mother board, slower than L1-26

factors affecting CPU

• clock speed(Hz)

• number of processor cores

• cache size + type

clock speed

number of instructions in a single processor core carried out per second

• aka clock cycles, measured in hertz(Hz)

overclocking

increasing CPU speed in basic input/output system(BIOS) excessively

• causes CPU to work too hard, leading to overheating

• some instructions are not executed in time, which leads to corrupt data

core

processing unit which receives instructions & performs calculations

dual cores

2 CPUS working

• each may have their own L2/3 cache, performing FDE at the same time & performing instructions

• without a software that supports it, only 1 core can be used.

parallel processing

allows different instructions from the same program to be ran at the same time

• dual core doesn’t mean twice the speed, as some tasks need to execute in order(sequential)