Senior 3 Computer Studies Memory and Storage Senior 3 Computer Studies

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

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

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

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

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

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.

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.

How an optical disc operates

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

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

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.

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…

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.

Hard Disk Drive (HDD) parts

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.

Different sectors

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

References and Further reading http://computer.howstuffworks.com/hard-disk.htm https://en.wikipedia.org/wiki/Hard_disk_drive http://www.easeus.com/resource/file-allocation-table-FAT.htm https://support.microsoft.com/en-us/kb/140365