We also divide the Instruction Set into four parts namely
- Arithmetic Instructions
- Logical Instructions
- Data Transfer Instructions
- Branch Instructions and I/O, Stack, Machine Control Group Imstructions
A - represents the accumulator.
B,C,D,E,F,H,L - represents the general purpose registers.
[A] - represents the contents of the registers A.
Similarly , [B] represents the contents of register B . i.e the square brackets represents the contents of the particular register.
[M] - represents the contents of memory location specified by the address M = xxxx ( 16 bit address ).
Double square brackets : e.g: [[B]]
If  = 12 , [B] = 4200 , then [[B]] =  =12.