3.3 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

ROM

  • stores boot instructions / BIOS
  • instructions stored on rom cannot be edited
  • is non-volatile memory

What is stored on RAM?

  • Start up instructions/bootstrap instructions
  • Firmware

ROM VS RAM

Static RAM VS Dynamic 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
  • 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

Differences between primary and secondary storage

  • Primary storage is directly accessible by the CPU
  • …whereas secondary storage is not directly accessible by the CPU
  • -Primary storage stores the data that is currently in use
  • …whereas secondary storage stores user’s files/data
  • Primary storage normally has a small capacity
  • …wherease secondary storage normally has a larger capacity
  • Some parts of primary storage are volatile
  • …whereas secondary storage is non volatile
  • some parts of primary storage the data cannot be changed
  • …whereas data in secondary storage can be changed
  • primary storage has faster access speeds to data
  • …whereas secondary storage has slower access speeds to data

Secondary Storage

Purpose of Secondary Storage

  • For non-volatile/permanent storage of files and data
  • To store data that is not currently required by the CPU
  • To store data to transfer it to another computer

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)

  • Flashes data onto chips
  • Uses transistors
  • Uses NAND/NOR technology
  • Uses control gates
  • Uses flow gates
  • controls the flow of electrons

Magnetic storage (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
  • Magnetic field determines binary value
  • Data is read and written using electromagnets

HDD vs SSD

  • SSD
  • SSD: Faster transfer speeds
  • SSD: Quieter operation
  • SSD: More reliable due to no moving parts
  • SSD: Less power required for operation
  • longevity is questionable due to set read/write cycles
  • HDD
  • HDD: cheaper per unit of measurement
  • HDD: More reliable, capable of more 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) shines 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

Difference between Optical and Solid State

  • Solid state has no moving parts
  • …otpical does have moving parts
  • Solid state is faster to access data
  • …optical is slower to access data
  • Solid state uses less power to operate
  • … optical uses more power to operate
  • solid state runs quietly
  • …optical makes more noise
  • solid state is more durable
  • …optical is less durable
  • solid state storage has a large storage capacity
  • …optical has a much smaller limit to its storage capacity
  • solid state is more expensive per GB of data
  • …optical is cheaper per GB of data
  • solid state stores data onto chips/transistors
  • …optical stores data by using lasers burning pits and lands onto a disk

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)

Sample question: A computer has pages A,B and C that are stored in RAM. Page D needs to be sent to the RAM but the RAM is full. Page B is not needed immediately. Explain how Virtual memory is used in this scenario

  • The secondary storage/hard drive can be partitioned to create virtual memory
  • …and page B is sent to the virtual memory…
  • …which makes space for page D in RAM
  • …Once page A/C/D is not required/has been processed
  • …page B can be sent from the virtual memory back to RAM when it is required

Cloud Storage

  • A collection of servers
  • …that store data in a remote location
  • …that are accessed using an internet connection

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