representation of data in computer systems notes

Units

• basic unit is 0 or 1- this is a binary digit or bit
• 4 bits - nibble
• 8 bits- byte
• 1024 bytes- kilobyte
• 1024 kilobytes- megabyte
• 1024 megabytes- gigabyte
• 1024 gigabytes- terabyte

Numbers

binary to denary- write out into a table and then add up the headings with totals of 1

denary to binary- divide by 2 repeatedly noting the remainder until the answer is 0. the answer is the remainder column starting at the last value

adding binary numbers- use column method. you can carry 1's. number that comes out with more than 8 bits is called an overflow and it is an error

hexadecimal numbers- base 16 system. uses values 0-9 and then a-f.

hexadecimal to denary- split into separate values and times by the heading. then add these values together

denary to hexadecimal- divide by 16 repeatedly and record the remainders until the answer is 0.

Characters

• it is important that systems agree on the codes being used for characters if the data is to make sense
• in 1960 the American Standards Association agreed on a set of codes to represent the main character set used in telegraph systems
• ASCII- American Standard Code for Information Interchange. was agreed to deal with basic textual messages and included codes for all the main alphabetic characters, upper and lower case; all the numeric symbols, 0-9; 32 punctuation and other symbols…