Data Storage

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