1. Senior 3 Computer Studies
Memory and Storage
Senior 3 Computer Studies

2. Primary and Secondary Storage
Primary Storage
CPU
Main Memory
Secondary Storage
Removable storage
HDD

3. Primary and Secondary Storage
Primary storage of a computer refers to all storage devices that are directly connected with the CPU.
An example of a primary storage device is the random access memory (RAM), which is the main memory of the computer.
Secondary storage refers to all storage devices that are not directly connected with the CPU.
The Hard disk of the computer and other external storage devices are examples of secondary storage.
Primary Storage
Secondary Storage

4. Primary and Secondary Storage
Primary storage devices are volatile, which means that data is temporarily stored while the computer is switched on.
Secondary storage devices are non-volatile, which means that data remains retained in the storage device even after the computer is switched off.
Primary Storage / Volatile
Secondary Storage / Non-volatile

5. Serial vs Direct Access
Serial access is when data is retrieved sequentially from the start point to the end, example: old magnetic tape such as old music cassettes and back tape cartridges.
Direct access is when data is retrieved directly from the point where it is written (stored), examples include all modern magnetic hard disks, RAM, SSD’s, and other external storage devices.
Serial Access
Direct Access

6. Optical Devices Examples of Optical Storage Devices: CD-ROM CD-R
DVD-ROM
DVD-R
DVD-RW
CD-RW
DVD-RAM
Blu-ray Disc

7. Optical Devices
Optical devices store data as digital data dots in 1’s and 0’s (lands and pits).
Data on optical devices is written (stored) using light, usually a laser beam.

8. Disc Parts An optical disc drive is made up of the following parts:
A mount to place the disc on to.
A laser beam to read /write data.
A motor to spin the disc.

9. How an optical disc operates

10. Review Terms learnt and used in this lesson:
Primary and Secondary storage
Volatile and Non-Volatile
Optical devices – how data is stored
CD burners / re-writable data
Data dots – lands and pits
Different types of optical storage media

11. Different Storage Speeds
Fastest to lowest:
Solid State Drive
Hard Drive
Back- up tape
USB stick (pen drive)
DVD drive
Jaz drive (like external hard disc for storage)
CD-ROM
Compression disc drive
Floppy disc

12. Files are allocated in directories
Files are allocated in directories. Directories are special folders holding particular type of files. A directory is uniquely identified by its name. ex: Program Files directory contains only software programs.

13. The Hierarchical File Structure
A Hierarchical File Structure is a model by which all files in a system are organized using a top file directory to bottom approach.
For example if we had to organize a hierarchy of the School, who would be on top of the school hierarchy?
Now let us consider the Windows operating system…

14. Windows OS Hierarchical File Structure
Do you think it is correct?
This C:\ hard disk drive is actually the top directory of the hierarchy, but in Windows OS interface it is seen after the desktop.

15. Hard Disk Drive (HDD) parts

16. File Allocation Table (FAT)
FAT is a table that is used by the operating system to store data in the hard disk.
Data in a hard disk is saved in logical storage into Sectors.
Sectors are grouped together into Clusters.
A typical cluster size is either 2048, 4096, or 8192 bytes.
Every time a file is saved in the hard disk, the operating system creates a new FAT entry.
A file can be stored in more than one cluster.

17. Different sectors

18. How data is stored in HDD
An HDD stores data using magnetic fields (North-South poles) to store and read data on a platter disk.
N-S = 1
S-N = 0

19. References and Further reading