Primary Storage
- Main memory inside a computer / directly accessed by CPU
- eg. RAM + ROM
RAM
- Stores OS when running / data currently in use / instructions currently in use
- Volatile memory (contents removed when device powered down)
- RAM is temporary
What is stored on RAM?
- Currently running data
- Currently running software
- Currently running instructions
- Currently running utility software
SRAM vs DRAM
- DRAM: consists of many transistors and capacitors; needs to be refreshed constantly; less expensive than SRAM; consumes less power than SRAM
- SRAM: uses flip flops to hold each bit of memory; faster data access compared to DRAM; CPU cache makes use of SRAM
ROM
- Stores boot instructions / BIOS
- Instructions stored on ROM cannot be edited
- Is non-volatile memory
ROM vs RAM
- ROM: permanent memory; is non-volatile memory; data on ROM cannot be edited
- RAM: temporary memory; volatile memory; can be read from or written to; holds part of the OS/applications currently in use
Secondary Storage
- Internal memory device not directly accessed by CPU
- Non-volatile devices
- Used for long term storage of files
- eg. HDD/SSD
Solid State (SSD) — Operation/Description
- Uses flash memory
- Data is flashed on chips
- Uses NAND/NOR technology
- Writes (and reads) sequentially
- Uses transistors/control gates/floating gates…
- …to control the flow of electrons
- It is a type of EEPROM technology
- When data is stored the transistor is converted from 1 to 0 / 0 to 1
Magnetic Storage (HDD) — Operation/Description
- It has platters
- Platters/Disk divided into tracks
- Platter/Disk is spun (disks spin when in operation)
- Has read/write head that moves across storage media
- Read/Writes data using electromagnets
- Uses magnetic fields to control magnetic dots of data
- Magnetic field determines binary value
- Data is read and written using electromagnets
HDD vs SSD
- SSD: Faster transfer speeds; quieter operation; more reliable due to no moving parts; less power required for operation; longevity is questionable due to set read/write cycles
- HDD: Cheaper per unit of measurement; more capable read and write operations; not reliable, susceptible to damage if moved during operation
When to use HDD or SSD
- SSD: when transfer rates/speed is a priority
- HDD: when capacity/storage requirements are high
- HDD: typically used in large servers
Optical Storage (CD/DVD) — Operation/Description
- (Red) laser is used
- (Laser beams) shine onto surface of the disk
- It is rotated (at a constant speed) to be read
- Data is represented on the surface using pits and lands
- Surface is covered in a track (that spirals from the centre)
- Pits and lands represent binary values
- Pits reflect light back differently (to the area in between/land)
- Optical device can determine the binary value from the light reflection
Virtual Memory
How is virtual memory created and used?
- The hard drive is partitioned to create virtual memory
- When RAM is full
- …pages of data that are not required
- …are transferred from RAM to virtual memory
- When the data is required again the pages are transferred back to RAM
Explain why virtual memory is needed?
- To extend the RAM capacity
- …to stop software from freezing/crashing when the physical RAM is full
- To allow the computer to process the large amount of data required for eg. 3D modelling.
Drawbacks of virtual memory
- Disk thrashing
- …can lead to premature failure
- Operations in virtual memory run slower (as data on an HDD cannot be accessed as fast as RAM)
Cloud Storage
- Storage consisting of servers
- …that are often in a remote location
- …that are often maintained/backed up by a third-party company
- Storage that is normally accessed using a network (often the internet)
- Physical servers and storage are needed to store data in cloud storage
Public cloud:
- Storage environments where client and cloud storage provider are separate companies/organisations
Private cloud:
- Storage provided by a dedicated environment behind a company firewall; client and cloud storage provider are integrated and act as a single entity
Hybrid cloud:
- A combination of public and private; some sensitive data stored on a private cloud whereas other data can be stored on a public cloud
Advantages of using cloud storage
- Cloud storage can be free (for small quantities)
- No need for separate (high capacity) storage devices // saves storage on existing devices
- Can access data from any computer with internet access
- Most cloud data services will have in-built backup/disaster recovery
- Security could be better
- Can easily increase capacity
- Data can be easily shared
Disadvantages of using cloud storage
- May be less secure // cloud server host may have a data breach
- May lose access to data stored on a cloud server if internet connection is not available
- Relies on third party maintaining the hardware
- Could incur an extra cost