01101010 = 0110 1010 = 6A

Zeros On the Left

Octal Names
nibble	pattern name	nibble	pattern name
000	0	100	4
001	1	101	5
010	2	110	6
011	3	111	7

Sometimes documentation describes bit patterns in groups of three. Three-bit groups are named using the first eight pattern names of hexadecimal. This method is called octal notation . A bit pattern can be named using hexadecimal names, octal names, or many other notations.

01101010 = 01 101 010 =  152 (octal)
01101010 = 0110 1010  = 0x6A (hex)

Octal is awkward to use with 8-bit bytes. Bytes don't evenly split into octal pattern names. But you should know about it. Historically, some computer documentation used octal pattern names. Also, in several programming languages (C and Java among them) octal notation is signaled by a leading zero:

0152    (octal)    = 001 101 010 
0x152   (hex)      = 0001 0101 0010 
152     (decimal)  = 1001 1000 

I have lost an unfortunate number of hours in total despair over disfunctional programs that could not possibly be wrong, only to discover a constant buried deep in the code that started with a "0" when it should not have.

Adding zeros to the left of a pattern creates a new pattern. The new pattern has its own name. 0x0 = 0000 is a different pattern than 0x00 = 0000 0000. Sadly, people are not consistent about this, and depending on context, both patterns might be called "0x0".

When the number of bits is not a multiple of four it is conventional to add zero bits to the left, and then to name the pattern as usual.

10 1101 0101