2.2.3 Data storage
When referring to storage space, we use the term bytes (B). A single byte is a combination of 8 bits. Other measurements include:
- kilobytes (KB) − approximately one thousand (10^3) bytes
- megabytes (MB) − approximately one million (10^6) bytes
- gigabytes (GB) − approximately one billion (10^9) bytes
- terabytes (TB) − approximately one trillion (10^12) bytes
- petabytes (PB) − approximately one quadrillion (10^15) bytes
- exabytes (EB) − approximately one quintillion (10^18) bytes.
If you have never seen this symbol before ^ it is a common shorthand for a mathematical power. A power is a number that is multiplied by itself a number of times. For example 10 to the power of 2 (10^2) is 10*10 which is 100, again 10 to the power of 4 (10^4) is 10*10*10*10 or 10,000.
Over the years, the amount of available storage space has increased exponentially. For example, not long ago the storage space of hard drives was typically measured in megabytes. Today, terabyte hard drives are common.
There are three primary types of data storage:
- Local data refers to data that is accessed directly, by local devices. Hard disks, USB flash drives, and CDs/DVDs are examples of local data storage. See Table 3 for more information.
Table 3 Types of local data storage
| Optical drives | USB flash drives | Hard drives | External hard drives |
| An optical drive is used to write data onto a CD or DVD. These portable storage devices are inexpensive and easy to label and store. | USB flash drives are removable and rewritable. These portable storage devices can hold gigabytes of data. | Hard drives come pre-installed on most desktop or laptop computers. These devices store data on magnetic platters. They can store large amounts of data, 1 terabyte or more. | External hard drives that are enclosed in a case and are usually attached to your computer via a USB or Firewire port. |
- Centralised data is stored and shared from a single centralised server. This information can be accessed remotely by multiple devices over the network or the internet. Using a centralised data server can result in bottlenecks and inefficiencies, and can become a single point of failure.
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Distributed data is managed by a central database management system (DBMS). Distributed data is data that is replicated and stored in multiple locations. This allows for easy and efficient sharing of data. Distributed data is accessed through the use of local and global applications. With a distributed system, there is no single source of failure. Should one site lose power, users are still able to access data from the other sites. See Figure 9.
Figure 9 Distributed data
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