2.  Bits & Bytes Bits & Bytes  Units of data Units of data  Storage devices Storage devices  Storage Types Storage Types  Secondary Storage Secondary Storage

3. Bits & Bytes  Data consists of bits and bytes.  A bit is represented by a 0 or 1. (The 1 actually represents a small flow of current, and the 0 represents the absence of current).  A byte is eight bits stuck together in a chunk, one after the other, e.g.  A bit is the smallest unit of data. The word bit comes from Binary Digit. 0 1 1 1 0 0 0 1is a byte  Numbers that consist of just ‘0’s and ‘1’s are called binary numbers.

4. Bits & Bytes  As computers can only understand numbers, letters are stored and transmitted as numbers.  Each letter is stored and transmitted as a single unique byte, called its ASCII code.  ASCII stands for American Standard Code for Information Interchange  The ASCII code for the letter A is 65, but this is stored as a single byte of binary numbers…  When you press the ‘A’ key on a keyboard, it is this series of ‘0’s and ‘1’s that is sent to the computer. The computer recognises the series of ‘0’s and ‘1’s and displays the letter ‘A’.

5. Units of Data A byte is eight bits A kilobyte is a thousand bytes (1000) A megabyte is a million bytes (1000,000) A gigabyte is a billion bytes (1,000,000,000) A terabyte is a trillion bytes (1,000,000,000,000)  Units of data increase by a factor of a thousand. (Actually 1024, but 1000 is used for simplicity) A bit is a 0 or 1

6. The device which stores the data in computer Also known as memory. It is of two types 1. Primary memory 2. Secondary memory

7.  Primary storage RAM ROM  Secondary storage Floppy disk CD DVD Hard disk

8.  RAM stands for random access memory.  It is volatile in nature,it’s content are erased when power is turned off.  We can read as well as write through this memory.  ROM stands for read only memory.  It is non-volatile in nature,it’s content are not erased when power is turned off.  We can only read through this memory

9. The storage capacity of primary storage is not sufficient to store large volume of data hence additional memory is used, knowm as secondary memory. There are two methods of accessing data:  SEQUENTIAL ACCESS: Data is reterived in same sequence in which it is stored.  DIRECT ACCESS:Data can be access directly.  The storage capacity of primary storage is not sufficient to store large volume of data hence additional memory is used, known as secondary memory. There are two methods of accessing data:  SEQUENTIAL ACCESS: Data is retrieved in same sequence in which it is stored.  DIRECT ACCESS: Data can be access directly.

10. Secondary Storage devices  Backing storage is the permanent store of data on an internal hard drive, external hard drive, CD or DVD, memory stick, Zip disc, floppy disc, etc. Zip Disc Floppy Disc USB Memory Stick Hard Drive CD, DVD

11. Hard Disks are the main internal backing store usually found inside computers. The main benefit of hard drives is that they have a large storage capacity – 20 gigabytes or more. (1 Gb = 1024 Mb). Floppy disks are a common external backing store, however only store up to 1.44 Mb of data. CD-ROM (Compact Disk Read Only Memory) disks are optical disks that use the same technology as musical compact disks. They store up to 700 Mb of data and a laser beam is used to read the data off the disk. Secondary storage Device

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