Lessons 4 · 1 lessons · D.T. Kamaltdinova, D.M. Sayfurov. Informatics and Information Technology, Grade 5 (general editor F.M. Zakirova). “Nashriyot uyi Tasvir”, Tashkent, 2020
4
Coding information. Units of information
Textbook: pp. 17–22
GoalTell coding, decoding and encryption apart and work out the size of information in bits and bytes.
New words
coding: turning information from one form into another with special signs · kodlashencryption: coding information to keep it secret · shifrlashthe smallest unit of information (0 or 1) · bitbyte: 8 bits, enough for one character · bayt
Explanation
A code is a system of agreed signs used to express information. Turning information from one form into another with special signs is coding, and restoring the meaning of coded information is decoding. Coding can be numeric, symbolic or graphic: road signs, musical notes and Morse code (dots and dashes) are all codes. Coding information to keep it secret is encryption and opening it again is decryption; the science that studies this is cryptography. A computer stores all information using only two signs, 0 and 1. One 0 or 1 is one bit, and 8 bits make 1 byte: one letter or digit usually takes 1 byte. Units: 1 KB = 1024 bytes, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB.
Worked examples
The word “KITOB” has 5 characters. Each character is 1 byte, so its size is 5 bytes, that is 5 × 8 = 40 bits.
An e-mail has 8 paragraphs with 128 characters in each. The number of characters is 8 × 128 = 1024, which is 1024 bytes = 1 KB.
Class activity
“Secret note”: in pairs, pupils encrypt a short word by replacing each letter with the next one in the alphabet (A→B, M→N...) and the partner decrypts it. Then they tap “SOS” in Morse code (three short, three long, three short).
Practice
1
How many bits is 3 bytes?
24
2
How many different combinations can a 4-bit code make (2 × 2 × 2 × 2)?
16
3
Code table: 1 = A, 2 = I, 3 = L, 4 = M, 5 = K. Which word is the code “2 3 4”?
ILM
4
Why are 3 bits not enough to code characters?
3 bits give only 8 different codes, but there are more letters, digits and signs than that; 8 bits give 256 codes.