1. STORAGE DEVICES
Towards the end of this unit you will be able to identify the type of storage devices and their storage capacity

2. WHAT IS STORING ?

3. STORAGE CAPACITY
Storage capacities and file sizes are measured from lowest to highest in:
bits
bytes
kilobytes
megabytes
gigabytes
Terabytes

4. Relationship between measurement
8 bits byte
1024 bytes kilobyte
1024 kilobytes megabyte
1024 megabytes gigabyte
1024 gigabytes terabyte
1000 Terabyte Petabyte
1000 Terabyte Petabyte

5. ACTIVITY
PLACE THE FOLLOWING MEASURING UNIT IN TERMS OF THEIR STORAGE CAPACITY FROM SMALLEST TO LARGEST
bits
Kilobytes
Gigabytes
Terabytes
Megabytes
Bytes

6. STORAGE DEVICES USED IN A COMPUTER
A computer uses two types of storage.
A main store consisting of ROM and RAM, and
backing stores which can be internal, eg hard disk, or external, eg a CD or USB flash drive.

7. HOME WORK DRAW THE MEASUREMENT RELATIONSHIP TABLE 8 bits……….. 1 byte.
………………………….
………………….. 1 terabyte

8. MAIN STORE (COMPUTER MEMORY)
Main store (or computer memory) is divided into Read Only Memory (ROM) and Random Access Memory (RAM).
ROM (NON VOLATILE MEMORY)
ROM is memory that cannot be changed by a program or user. ROM retains its memory even after the computer is turned off. For example, ROM stores the instructions for the computer to start up when it is turned on again.

9. RAM RAM (VOLATILE MEMORY)
In the case of RAM, it is volatile (this means that when power is switched off all of the data in the memory disappears). Main memory is used to store data whilst it is being processed by the CPU. Data can be put into memory, and read back from it, very quickly.

10. ROM AND RAM

11. INTERNAL BACKING STORE-HARD DISK
The main internal backing store is a computer's hard disk.
A hard disk stores:
the operating system
software applications or programs
the majority of your data files
Note: Hard disks store large amounts of data - 200GB to 1TB is common in desktop computers. The data stored on a hard disk is retained until deleted, but it needs to be loaded into main store RAM before it can be used.

12. HARD DISK

13. ACTIVITY
1.Which of the following retains its data even after the computer is switched off? ROM RAM REM 2. What does RAM stand for? random accessible memory random access memory random allowable memory 3. What is a computer's main internal backing store? CD-ROM ROM hard disk 4. How best is the size of a hard disk measured? kilobytes megabytes gigabytes

14. ANSWERS
1.Which of the following retains its data even after the computer is switched off?
ROM RAM REM
2. What does RAM stand for?
random accessible memory random access memory random allowable memory
3. What is a computer's main internal backing store?
CD-ROM ROM hard disk
4. How best is the size of a hard disk measured?
kilobytes megabytes gigabytes

15. MAGNETIC STORAGE MEDIUM-Floppy disks
Floppy disks hold very small amounts of data, just 1.44MB and a computer needs a floppy drive to read them.
They are used to:
transfer small files of data from
one machine to another
backup important small files that are stored on your hard disk
store restricted files that you don't want other users of your computer seeing

16. MAGNETIC STORAGE MEDIUM-ZIP DISK
Zip disks are like large floppy disks but can store 250MB or more of data. To read them a computer needs a zip drive. Their use is similar to that of floppy disks.

17. MAGNETIC STORAGE MEDIUM- HARD DRIVES
Hard Drives- There are two types of Hard Drives. One is Internal that we studied earlier. The other is an Portable Hard Drive.
A portable hard-drive is one that is placed into a small case along with some electronics that allow the hard-drive to be accessed using a USB or similar connection. Portable hard-drives allow very large amounts of data to be transported from computer to computer.
HARD DRIVES ARE RANDOM ACCESS DEVICES

18. MAGNETIC STORAGE DEVICES- MAGNETIC TAPE
Magnetic tape are serial access devices and are used only where batch processing is used.
Advantages: (i) Tape is light and compact and easy to carry and yet it stores far more data than floppy discs.