3.3 Data Storage
Primary Storage
This is directly accessible by the CPU (includes , Cache, & )
RAM
Purpose is to store data, instructions, and software currently in use
Also called main memory
Faster write & read speeds than secondary storage
It's volatile (temporary memory) and all data is lost when the computer is switched off
Larger memory = better performance
Cache
Store frequently or recently used instructions and data
Faster write & read speeds
There are two levels of cache; level 1 is situated within the CPU, levels 2 & 3 are situated on the motherboard
More cache = better performance *
It's volatile and all data is lost when the computer is switched off
If you have too much cache, this will slow the computer down and it will take longer to find the data that you need.
ROM
Store the boot-up sequence (load the OS from secondary storage to RAM)
Non-volatile
Read-only
Secondary Storage
Not directly accessed by the CPU
Used for permanent storage
Non-volatile
Can be written to and read from
Data access speeds typically slower than primary storage
Have large capacity
Magnetic Storage
Hard drives are the main type of storage. It is made up of different metal disks coated with a magnetic material (called platters). Iron particles on each platter are magnetised to represent binary. Each platter is divided by concentric circles creating several tracks and wedge shaped sectors.
The hard drive spins the metal disks at high speed using a motor. A read & write arm (controlled by an actuator) moves the head over the surface of the disc to the location of the data. Data is written using electromagnets.
Solid State Storage
Solid state drives are made of transistors that are arranged in a grid layout. It uses NAND and NOR gates to persistently control the flow of electrons. Current flowing represents 1 and the opposite applies.
Optical Storage
These include (from the largest capacity to the lowest capacity):
Blu-rays
DVD-RW
CD-RW
CD-R (cannot save data onto them)
All of these work by shining a laser at the disk and processing the reflection. An arm moves the laser across the surface of the disk.
In CR-Rs, a laser burns the data onto the disk creating pits and lands. The laser is also used to read the data. When the light is reflected back or not is captured by a sensor and can be interpreted as a change in the binary.
In CD-RWs, the chemical composition of the disk is changed to represent binary (but it can be overwritten).
Virtual Memory
This is secondary storage but acts as RAM when RAM is full. This prevents a computer from crashing. Data that needs to be accessed by the CPU is switched by the OS from VM into RAM and vice versa. This is called page switching.
Sample answer:
When RAM is full Secondary storage (HDD / SSD) can be partitioned to make virtual memory The data that is not needed can be sent to the virtual memory Once some data has been used or is no longer needed, then the data from the virtual memory can be transferred back to RAM
Cloud Storage
This is the concept of storing data on remote servers that can be accessed via the internet. The physical place where the data is stored is managed by a hosting company. This company is in charge of keeping your data safe and backing it up. The data can be accessed at any time and place. There is potentially limitless storage (although it comes with a cost).
Having online storage makes it easier to share files and collaborate with others but if you're without an internet connection, access to your data is not possible.
Once cloud storage centre is more environmentally friendly that millions of individual servers. However, data being sent over the internet has the potential to be intercepted by hackers.
Exam Questions
Last updated