Storage Devices

Storage devices, such as hard disk drives and USB flash drives, are used to store application and user data. This storage is persistent, it doesn’t forget the data it is storing even when the computer is turned off.

As well as the store our files and application on our device so we can use them, storage is also important for backup and recovery, should our data be harmed. There are a number of technologies that are particularly useful for this.

In this lesson, we’ll learn about:

  1. Types of storage devices and their features that affect performance.
  2. Data storage and recovery systems.
Media Attachments: Presentation

1. Types of Storage Devices

Storage Devices

As mentioned in the lesson introduction, storage devices are used to store application and user data. These can be internal which will be used to hold data for the running of the computer, or external which are useful for transferring files to other devices, as well as for backup.

Some example storage devices include:

Hard Disk Drives

These are commonly used as the primary storage devices in a computer system, particularly servers and desktop computers. It can be used as an external portable storage device too, but it isn’t as ideal for this as other options.

HDDs (Hard Disk Drives) are a form of magnetic storage. They consist of a number of disks made of magnetic material that we call platters. The hard disk drive magnetises and demagnetises billions of tiny individual areas on the platter.

Because computers store all data in 1’s or 0’s (known as binary), we can store our data this way as a magnetised area represents a 1 and a demagnetised area represents a 0.

Advantages

  • HDDs offer a big storage capacity at a relatively low cost. You can get a terabyte HDD for less than £50.
  • They are considered a reliable storage method as they have a long life span and tend not to fail outright.

Disadvantages

  • HDDs have a relatively slow read/write speed, particularly when compared to their main alternative, the Solid State Drive.
  • They have a number of moving parts, which means knocks can easily damage the device. This makes it generally a risky option as a portable storage device.
  • They’re larger than alternatives like SSD’s. This makes them inappropriate for many smaller devices like laptops & tablets.

Solid State Drives

These are used often as a portable storage device with a large capacity. However, they are also commonly used as the primary storage device in laptops and recently in desktop computers.

SSDs (Solid State Drives) are a form of flash memory storage. They store data using semiconductor chips. These chips can be switched to either an “on” or “off” state. The “on” state representing a 1 and the “off” state representing a 0.

Advantages

  • SSDs have very fast read/write speeds, especially compared to hard disk drives. This makes it faster to turn on your computer, load programs and save files.
  • They also consume less power than HDDs. This makes them very useful for devices that often run off of battery power, such as laptops.
  • Because they have no moving parts, they are less likely to be damaged by knocks and bumps, which makes them useful as portable storage devices.

Disadvantages

  • SSDs are quite a bit more expensive than HDDs. A 1 terabyte SSD will cost you over £200 (compared to under £50 for an HDD).
  • Because of this heightened cost, this means that generally, SSDs will have a lower storage capacity than HDDs.
  • SSDs have a finite number of writes before they no longer work. This makes them less useful for devices that require regular writing to the disk (like many servers).

SD Cards and USB flash drives are additional forms of flash memory storage. These are specially designed as external portable storage devices though as they are very small and light-weight.

As they are so much smaller than SSDs they will not offer as much storage/will be more expensive for similar levels of storage.

Optical Disk Drives

CDs, DVDs and Blu-Ray disks, are all examples of optical disks. They’re most commonly used for storing music, films, tv & software, for distribution by suppliers (i.e. game publishers distribute games on disk to retail stores to sell).

All of these different types of disk are a form of optical storage. This works by using a laser to mark the disks in a pattern. A light is then bounced off the disk and is read back differently depending on whether the light bounces off a marked or non-marked area. Marked areas are known as “pits” and represent 0’s in binary, non-marked areas are known as “lands” and represent 1’s in binary.

Advantages

  • Optical disks are extremely cheap to produce and buy. You could buy 50 Blu-Ray Disks for less than £35, which would be even cheaper for large businesses wanting to distribute their software/films.
  • They’re a small storage media, which makes them highly portable. This is another reason why they’re used for distributing things like software and films.

Disadvantages

  • An individual optical disk has quite a small storage capacity. A Blu-Ray can store up to 50GB of data.
  • Optical disks are also easy to damage. They’re quite flimsy, and also are easy to scratch which can damage the data it is storing.
  • Optical disks only work for a finite number of writes. CDRW disks, for example, can be written to around 1000 times.

Further Thought

We mention SD cards and USB flash drives are forms of flash storage. When would you use these storage devices instead of an SSD?

2. Data Storage & Recovery Systems

Data Storage & Recovery Systems

There are a number of technologies used with data storage to help protect data from harm and help us to recover damaged data. Two of these technologies we’ll look at now.

RAID

Redundant Array of Independent Disks is a technology used to store data in multiple locations across separate disks. These disks will appear as a single logical disk in your OS. This will be able to provide data redundancy to protect data as well as to provide performance improvements.

There are different RAID levels that provide different benefits. For the most part, these different levels use two main techniques, disk striping & disk mirroring.

  • Disk Striping – dividing data into multiple blocks and sharing these blocks across multiple disks. This helps performance as you can read & write concurrently as each disk can perform a separate operation.
  • Disk Mirroring – duplicating data across multiple disks, so that if something happens to one disk, you have a redundant copy of the data so nothing is lost.

NAS

Network Attached Storage is a device that we can connect to a network that allows us to access our files from a central location. So we can store our data on the NAS device instead of/as well as on our computer system. It is essentially a very simple file server.

NAS devices are very useful for sharing files between multiple users so we can work collaboratively on these files. It also allows us to work on different devices on the network and still have access to our data.

NAS is also popular for backup and recovery purposes. We can automate backups of our data to the NAS device so that if something happens to our computer or the data on it, we can recover from the backup.

Further Thought

We mentioned above that there are different levels of RAID. Research about these levels and the differences between them.

Lesson Summary

So to summarise what we’ve learnt in this lesson:

  • Hard disk drives are a form of magnetic storage commonly used as the primary storage devices in a computer system.
    • They have a large storage capacity & are reliable.
    • However they’re slow & large compared to SSD and can be easily damaged by knocks.
  • Solid state drives are a form of flash storage often used as a portable storage device and as primary storage in laptops & recently desktops.
    • They have fast speeds compared to HDDs, consume less power than HDDs and are not easily damaged by knocks.
    • However, they are comparatively expensive compared to HDDs and have a lower storage capacity. They also have a limited number of writes.
  • Optical disks, like CDs, DVDs & Blu-Ray, are a form of optical storage commonly used for storing music, films, tv & software, for distribution by suppliers.
    • They are very cheap and are highly portable.
    • However, their storage capacity is relatively small and they can be easily damaged.
  • RAID is a technology used to store data in multiple locations across separate disks. This provides data redundancy and improved performance.
  • NAS is a device that we can connect to a network that allows us to access our files from a central location for backup and sharing files.