Hardware

• holds all crucial hardware components 

• has many buses for transferring data

• measured in bus speed in MHz 

• holds computers settings e.g time and date 

• links CPU to memory and other hardware via buses

• receives and sends signals to hardware for the CPU 

• control unit:  fetch-decode-execute cycle 

• arithmetic logic unit (ALU): mathematical and logic operations on data 

• registers: fast, on-chip memory inside 

• internal clock: connects to system clock 

• internal buses: connects components

•  logic gates: controls flow of information 

Performance is affected by the number of cores, the clock speed and memory 

used by the CPU to carry out instructions

1) fetches instruction from main memory by using the addess bus to find data from the place it wants

 2) takes it to the current instruction register in the processor

3) decodes the bit pattern into the instruction to be carried out 

4) executed and results stored in memory 

The CPU cannot fetch data directly from the hard drive so a computer has cache. 

Cache - a small amount of memory in the CPU which temporarily holds instructions that the CPU is likely to reuse 

• a very high speed memory
• The CPU checks the cache before getting data from the RAM (which would be slower) 
• more cache = more data closer to CPU = faster 

Different Grades of Cache :

• L1: a CPU chip ,smallest, fastest
• L2+ L3: built between CPU and RAM, longer to access, bigger than L1 

Cache organisation:

• temporary locality- likely to need access to same source again
• spatial locality- likely to need access to simular data again 
• sequential locality- likely to need access to s+1 

Volatile memory- requires a power supply to store data 

RAM (Random Access Memory) is volatile 

Normal RAM is called DRAM (Dynamic RAM)

•  a transistor and a capacitor to store 1 bit of data (a very small space)
• needs to be freshed as it doesn't last very long. 

SRAM (Static RAM)

•  six transistors to store each bit of data rather than 1
•  doesn't need refreshing as often
•  takes up more space to store a bit
• more complex to build. 

Non-Volatile: retains memory after the power supply has stopped, permanent. 

ROM (Read Only Memory) is a non-volatile, flash memory chip 

PROM (Programmable ROM) can be programmed by the user but only once and it is very cheap.

EEPROM (Electrically Erasable Programmable ROM) can be easily updated and reprogrammed (contained in a smart phone) but is more expensive. 

A magnetic storage device uses moving read/write heads that contain electromagnets.

Examples: hard disk drive (HDD)

Advantages:

• very large storage capacity 
• faster than optical disk 
• data is not lost
• cheap per MB compared to other storage media 
• easily replaced and upgraded

Disadvantages:

• moving parts that don't like movement and can easily break
• crashes can damage surface of disk leading to lose of data
• uses a large amount of power 
• can be noisy 

An optical drive uses light/ lasers  to read data.

Examples: CD, DVD, CDR, DVDR, DRR

Advantages:

• easily to store 
• portable 
• read by a vast number of devices
• easy to use
• long lasting if taken care of 

Disadvantages:

• data written on CDR, DVDR and DRR are permanent and can't be changed 
• special drives to read them
• expensive per GB/TB compared to other methods
• easily scratched, broken or damaged by intense heat and/or  light

Solid State Storage uses special transistors that retain their state even when there is no power; they have no moving parts. 

Examples: SSD (Solid State Disk), USB Flash Drives, Micro SD cards 

Advantages:

• read faster than normal hard drives
• lightweight
• durable
• require less power
• portable
• silent

Disdvantages:

• expensive per MB than magnetic disks
• only erased and rewritten about 100,000 times 
• can be slower and have a limited storage capacity 

• can be programmed to control devices
• in a large number of everyday objects
• a small computer with a CPU, some RAM to store variables and some input and output devices.
• programmed by a basic stamp using the BASIC programming language to actual code. 

Contains:

• actuators- controls the output and converts energy to motion
• sensors- measures a physical quantity and converts it to a signal to make a decision from  the metal pins in it