Chapter 03 – Storage Devices and Media A storage device is something that has the ability to read and write information to and from storage media (e.g. CD/DVD writer or tape drive). The components that store the information, such as CDs and DVDs, hard disks and memory cards are the storage media.
Backing up data
What is backing up of data?
How often should it be done? Backing up on a regular basis is considered good computing practice and it is wise to set up a system that backs up files automatically. At school we back up every two hours, whilst at home it would be sensible to back up daily.
Where should a backup be stored? In a business, the backup is stored away from the main storage device, usually in a different building altogether. This is in case of fire, etc. in the main location which could destroy the original and the backup.
Why backup data?
Backups and viruses It is possible that a virus could unintentionally be added to the backup files. When the original machine is cleaned of viruses and the backup files re-loaded, the virus would also be re-loaded. This means that it is essential that virus protection on the original files is up-to-date and running.
Backup Models The following are popular models for backing up information 1. Manually choosing a selection of files to be saved onto a disk. This is useful for backing up a small selection of essential files. It is known as an ‘unstructured backup’
2. Taking a complete image of a computer and storing it in the event of a system crash. There are software tools that can do this, but it does take time, which means it is suitable for regular use. This is referred to as a ‘full system backup’
3. After a full system backup, backups are made at regular intervals of whatever has changed since the initial and following backups. This means that only small amounts of information are regularly saved, and users can look back at a system at a specified date in the past. This is known as an ‘incremental backup’
4. If a fire burns down an office of computers and the backup drive is permanently plugged in, then it too will be lost. Using an off-site backup minimises the risk of losing data by making sure that the drive or disks used are kept elsewhere, ideally in a secure location. This is called an ‘off-site backup’
Backup Solutions Depending on the needs of the user, there is a number of solutions available ranging from practical to commercial options: 1. Manually copying files – simplest solution involves copying files to a USB hard disk 2. Software Backup – Using a software programme to automatically backup files at a scheduled time such as late at night 3. Mirroring (often called RAID) – Two or more hard disks are linked in such a way that data is written to both at the same time, creating clones of each other. If one drive fails, the other is still accessible 4. Online or remote backup – using 3rd party software, files are backed up via the internet to an online server (charged by the hosting company). This is a key element of cloud computing.
Task 1: Create a table with the following headings: Type
Information to back up
What would happen if lost
School Graphic designer Designing pages of a popular newspaper Hospital
For each, write a list of all the information you think would be important to back up, and describe what would happen if it were lost.
Task 2: Ask a family member to find out what type of back up model / solution they have in place at their place of work. Type up a paragraph to explain these using examples.
Types of access
The way data is accessed on different storage devices can vary significantly. Below are the two main methods of accessing data.
(serial or sequential access) Primarily used on magnetic tape systems and used when:
Direct access Used with magnetic disks and optical media:
Updating Serial access
Updating Direct access
When a magnetic tape needs updating, an additional tape is required so that the old information can be merged with the new data (often on another tape itself, although this doesn’t have to be the case).
When updating media that uses direct access, the new data is written to the next available location and its position is calculated using the built in algorithm.
Old data stored on magnetic tape New tape with merged data New data to be merged with old data
Main or Internal Memory
Introduction Memory used by a computer system when processing or storing information. RAM can be read and written to while using programmes; the more RAM a system has, the faster it will run. ROM holds permanent data that cannot be changed; it contains the essential program drivers needed to start your computer
Backing storage media
Introduction Backing storage devices ensure that data is stored permanently (unlike RAM) and can then be used again at a later date. The devices can be internal or external and will fall into one of three categories:
Magnetic Media Fixed hard disk (uses direct access) Available on all computers and are the main method used for data storage; it stores the OS and applications software. These need the Hard Disk to allow them to quickly retrieve and save data.
Uses: •
Store operating system and working data
•
Storing applications software that need fast retrieval and storage of data
•
Real time systems (e.g. robots, control of a chemical plant) use fixed hard drives
•
Online systems (e.g. booking airline tickets, automatic stock control (EPOS)) use fixed hard drives
•
Used in file servers on computer networks
Advantages
Disadvantages
Magnetic Media - continued
Portable hard disk (uses direct access) Similar to fixed hard disks but are usually connected to the computer via a USB (Universal Serial Bus) port.
Uses: •
Can be used as backup systems to prevent loss of data
•
Can be used to transfer data, files and software between computers
Advantages
Disadvantages
Magnetic Media - continued
Floppy disks Now rarely used
Uses: •
Where small files need to be transferred / stored (e.g. text documents)
•
Some older computer systems might still have a floppy drive
Advantages
Disadvantages
Magnetic Media - continued
Magnetic Tapes (serial or sequential access) Uses: •
Batch processing applications (clearing bank cheques; utility billing (gas, electricity, water) and producing pay slips. In these applications, there is no need for any specific processing order and speed of access is not important.
•
They are used as large scale backup media.
Advantages
Disadvantages
Optical Storage Media
CD-ROM and DVD-ROM Read only memory so can be read from and not written over.
Uses: •
CD-ROMS are used by manufacturers to store music files and software, computer games and reference software (such as an encyclopaedia)
•
DVD-ROMS have a much larger storage capacity than CD-ROMS and are used to store films. They are increasingly used to store more sophisticated computer games and data.
Advantages
Disadvantages
Optical Storage Media - continued CD-R and DVD-R ‘R’ stands for recordable and means that the disk can be written over once.
Uses: •
CD-R used for home recording of music
•
DVD-R use for home recording of films
•
To store data to kept for later use or to be transferred to another computer
•
Used in applications where there is a need to prevent the deletion or over-writing of data
Advantages
Disadvantages
Optical Storage Media - continued
CD-RW and DVD-RW ‘RW’ stands for Rewritable and can be written over several times. Unlike CD-R / DVD-R they don’t become ROMs. The system allows data to be written, erased and re-written many times.
Uses: •
Used to record radio and television programmes, but can be recorded over time and time again.
•
Used in CCTV (Closed circuit television) systems.
Advantages
Disadvantages
Optical Storage Media - continued
DVD-RAM Unlike other optical media DVD-RAM allows reading and writing to the disk at the same time. This makes it possible to watch already recorded television at the same time as another programme is being recorded.
Uses: •
In recording devices such as satellite receivers to allow simultaneous recording and playback.
•
Used in camcorders to store films
Advantages
Disadvantages
Optical Storage Media - continued
Blu-Ray Disks Largest capacity of all the optical media and can be as much as 100Gb.
Uses: •
Home entertainment systems
•
Storing and playing back films (1 x 2hr HD film = 25Gb)
•
Can be used as data storage or for backing up HDD
Advantages
Disadvantages
Solid State Media (Flash Memory)
Solid state Disks They are beginning to replace traditional magnetic hard disks, especially in laptops as they are thin, have very fast access times and are very robust. As they have no moving parts, they consume much less power.
Uses:
Advantages
Disadvantages
Solid State Media (Flash Memory) - continued
Memory sticks / pen drives Can store many Gb of data and are usually connected to the computer using a USB port with the power to operate them being provided by the host computer.
Uses: Can be used as a “dongle� for additional security as software requests a validation key from it. This means that for software to be pirated the key on the stick would have to be cracked first Another form of security is to actually have a part of the software stored on the dongle in encrypted format Transporting files between computers or as a backup store
Advantages
Disadvantages
Solid State Media (Flash Memory) - continued
Flash Memory Cards These are a form of EEPROM (electrically erasable programmable read only memory) and are another example of a solid state memory.
Uses: Store photos on digital cameras. Mobile phones use them as memory cards In MP3 players to store music files As a backup store in hand held computer devices
Advantages
Disadvantages
Storage size summary
Storage device or media
Typical capacities
CD
700 Mb
DVD
4.7 Gb
DVD RAM
4.7 Gb
BLU-RAY
25 Gb
PEN DRIVE
2 – 32 Gb
FLASH MEMORY CARDS
2 – 32 Gb
PORTABLE DISK DRIVE
320 Gb – 1.5 Tb
SOLID STATE DRIVE
100 – 500Gb
HARD DISK DRIVE
1 – 4 Tb
MAGNETIC TAPE
500 Gb – 5 Tb
File size summary
8 bits
1 byte
1024 bytes
1 kilobyte (kb)
1024 kilobytes
1 megabyte (Mb)
1024 megabytes
1 gigabyte (Gb)
1024 gigabytes
1 Terabyte (Tb)
Word processed document
100 kb
eBook
500 kb
MP3 Track
5 Mb
Digital Photo
3 Mb
Film
1.2 Gb
Past Paper Questions 11/J/10
11/N/10
11/N/11
11/J/12