Systems architecture + Memory and storage

computer

electronic device which takes input

CPU

processes data

whats speed of CPU measured in

Hertz

what factors affect CPU speed

clock speed

cache size

number of cores

how CPU and RAM work together

CPU transfers data and instructions between CPU and memory

CPU retrieves instructions and data from RAM , storing them temporarily in its registers and cache for faster access during processing

CPU performs calculations, executes instructions, and manipulates data stored in RAM

RAM

main memory

ALU

Arithmetic and Logic Unit

does arithmetic calculations and makes all logical decisions

CU

control unit

controls flow of data

Fetch

fetches instruction from RAM

Decode

decodes the instruction

Execute

carries out instruction

FDE

works in a cycle

CPU gets instruction from main memory, using Program Counter (PC) to determine memory address

MAR holds address

CPU interprets fetched instruction's to determine operation to be performed

CPU carries out operation specified by the decoded instruction

memory access register (MAR)

Holds address of where data is to be fetched or stored

Memory Data Register (MDR)

contains data being fetched or stored

Program Counter (PC)

holds address of next instruction

Accumulator

Stores results of calculations

dual-core processor

single chip that contains two processors

cache

fast memory

temporarily holds instructions processor is likely to reuse

why is cache needed

temporarily holds instructions processor is likely to reuse

faster processing as processor does not have to wait for data to be fetched from RAM

see notes for cache speed

why is cache usually small

more cache, faster computer runs

cache is more expensive to build than RAM

level 1 cache

extremely fast transfer rates

very small

holds most frequently used instructions and data

level 2 cache

slower

bigger in capacity

hold data and instructions that are needed less frequently

stored-program

instruction and program data stored in same memory

embedded systems

computer system with dedicated function in larger system

primary storage

ram, rom, registers + cache
holds data and instructions needed by cpu
cpu gets data quicker here than secondary

RAM compared to ROM

bigger
read and write
volatile
holds programs and data in use by cpu

ROM compared to RAM

smaller
read only
non-volatile
holds start up instructions for computer

virtual memory

needed when there is not enough physical RAM to store open programs

where is virtual memory held?

hard disk

when are programs transferred out of RAM?

not being executed

when are programs transferred back to RAM?

when needed

why is secondary storage needed?

ROM is read only and RAM is volatile

what is secondary storage needed for?

storing programs + data when power turned off

semi-permanent storage of data that can change

backup + archive of data files

optical storage

low storage capacity

slow to access data

thin/lightweight/portable

examples of optical storage

CD-R/RW

DVD-R/RW

Blu-Ray

solid state storage

medium storage capacity

very quick to access data

no moving parts (reliable)

no noise

low power

no need to fragment

limited number of read/write cycles

expensive

examples of solid state storage

SSD

Memory sticks

Flash memory cards

magnetic storage

high storage capacity

quick to access data

has moving parts, which eventually fail

examples of magnetic storage

hard disk drive

tape