Memory & Storage - 1.2.1
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What is RAM?
Random Access Memory Main memory in a computer where data, files and programs are stored while being used When a computer system boots up the OS is copied from the secondary storage to the RAM When software applications, documents and files are opened they are copied from the secondary storage to the RAM
Features of RAM (4):
Volatile memory - temporary, requires power to retain Reads & writes Easily upgradable Faster than secondary storage but slower than cache
What is ROM?
Read Only Memory Built into the motherboard, contains all the instructions for a computer to start up (BIOS) As soon as computer starts CPU reads instructions from ROM
Features of ROM (3):
Non-volatile memory Only read Can’t change the information on it
What is virtual memory?
Used when RAM is full so data is moved to a location secondary storage called virtual memory for more space. When data is needed again it needs to be moved back to RAM which is quite a slow process Risk of hard disk thrashing
What is primary storage?
Memory that the CPU can easily access, e.g. registers, cache, ROM, RAM Mostly volatile, fast at reading/writing
What is secondary storage?
Where all data is stored when not in use Non volatile, read/ write speeds are much slower Magnetic, optical & solid state
Why do we need secondary storage?
It is non-volatile and long-term so if the computer switches off nothing is lost unlike with RAM.
How does solid state roughly work?
By trapping electrons between two plates. Can be written and overwritten like RAM.
Benefits of solid state (4):
Non volatile - contents are retained if computer switches off No moving parts - so produces less heat and therefore components last longer Also is more portable without moving parts Faster than HDD
Drawbacks of solid state (2):
Expensive Short life span
Examples of solid state:
Flash drives SSD Laptops/computers
How do magnetic devices work (6 steps)?
Uses magnetic fields to magnetise tiny individual sections of a metal spinning disk. Each tiny section represents one bit. A magnetised section represents a binary ‘1’ and a demagnetised section represents a binary ‘0’. As the disk is spinning, a read/write head moves across its surface. To write data, the head magnetises or demagnetises a section of the disk that is spinning under it. To read data, the head makes a note of whether the section is magnetised or not.
Types of magnetic (2):
HDD Laptops/computers Tape
Benefits (2) & Drawbacks (2) of HDD laptops/desktops:
Cheap for amount of storage Large storage Shock damage Not good with magnets - strong magnetic field could erase the data
Benefits (1) & drawbacks (3) of tape:
Huge storage Very slow Sequential access - must read everything in the order of the file to get to wanted part Also not good with magnets
How do optical devices work?
Uses a laser to scan the surface of a spinning disc with tracks and lands which change how the light is reflected from the laser
Benefits (2) & drawbacks (2) of CD’s:
Cheap to mass produce Long life span as it’s plastic Slow Easily damaged
Which has the fastest and slowest read/write speed?
Fastest - SSD Slowest - optical disc
Which has the cheapest and most expensive cost per GB?
Cheapest - magnetic tape Priciest - SSD
Which has the lowest and highest capacity?
Lowest - optical disc Highest - tape