GCSE    Basic Electronics    Questions 0 to 35   -->  View All  

Binary is the base 2 number system counting 0, 1, 10, 11, 100, 101, 110, 111, 1000, etc.

    Thanks xkcd

Decimal and Binary - Everyone

Decimal Numbers

These are used in everyday life and are so familiar that many important features get forgotten.

• There are ten symbols. These are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
• 9 + 1 = 10.
• 10 + 1 = 11.
• Counting from 0 to 9 is very familiar.
• For numbers greater than 9, a second column is needed.
• For numbers greater than 99, a third column is needed.
• The right hand column is the least significant. The numbers count in ones.
• The left hand column is the most significant. With three columns, the left hand column counts in hundreds.
• The Columns: 10000 - 1000 - 100 - 10 - 1 in decimal numbers.

Binary Numbers

• There are two symbols. These are 0 and 1.
• 1 + 1 = 10.
• 10 + 1 = 11.
• There are 10 kinds of people. Those who understand binary and those who don't.
• Counting in binary: 0, 1, 10, 11, 100, 101, 110, 111, 1000 etc. Since there are only two symbols, you need to add a new column often.
• For numbers greater than 1, a second column is needed.
• For numbers greater than 11, a third column is needed.
• For numbers greater than 111, yet another column is needed.
• The right hand column is the least significant. The numbers count in ones.
• The left hand column is the most significant. With three columns, the left hand column counts in fours (in decimal numbers).
• The Columns: 128 - 64 - 32 - 16 - 8 - 4 - 2 - 1 in decimal numbers.

Binary Bit

One binary digit. A zero or a one.

Byte

A group of eight bits. Computer data is usually stored and processed in bytes or pairs of bytes or even groups of four or eight bytes.

Nybble

This is half a byte or four bits. The word was originally a joke but the term proved useful.

In an eight bit byte such as 11100111, the HIGH nybble is 1110 and the LOW nybble is 0111.
They are called low and high because the low nybble is worth 0 to 15 in decimal numbers and the high nybble allows numbers up to 255.

Nybble is often spelled nibble. Internet flame wars rage over this!

Word

Grouped bytes are called words. 64 bit computers common in 2015 work with 8 byte groups. 8 x 8 = 64 bits in the word.

LSB and MSB

In this number: 11100111 the

• left most bit is worth 128 and is called the Most Significant Bit (MSB)
• right most bit is worth 1 and is called the Least Significant Bit (LSB)
• In a four bit number, the MSB is worth eight.

Getting bits back to front causes serious errors so it's important to pay attention to this.
This mistake crops up frequently when designing binary counters to reset on specific numbers like ten.

Decimal Binary Conversion

• The columns from left to right are worth 8, 4, 2 and 1.
• Column 8 is the MSB or most significant bit. Column 1 if the LSB or least significant bit.
• The binary counts from 0 to 15 and the zeros and ones indicate the presence or absence of the 8, 4, 2 or 1 depending on which column they are in.
• For example 0101 means No 8, yes 4, no 2 and yes 1.
• Add them up and you get 4 + 1 = five.

Converting Larger Numbers

• Jot down a table like this with the column values. Write the binary number below the column headings.
• Add up the numbers wherever there is a binary one to get the total.
• To do a decimal to binary conversion, work from left to right and ask if you need each number. If you do, write a one. If not, write a zero.

Little and Big Endian

A 64 bit computer could put the most significant byte at the left or right end of the group of eight bytes. Different computer manufacturers use both schemes. This makes it more difficult to store and transfer data between incompatible systems. Data munging is needed to reverse the byte order. Internet flame wars rage over this topic.