What is the difference between assembly and machine language?

Answer 1

Machine language is pure binary, just opcodes and operands.

Assembly language use the 3 or 4-letter Mnemonics and operands.

Answer 2

Machine code is the 8/16 bit binary code actually processed by the CPU. Assembler is a higher level "short hand" which needs compiled or interpreted to become operational machine code so

mov AX, 4C00 ; move 4C00 into the AX register
int 21 ; execute software interrupt 21

in assembler becomes

B8 00 4C CD 21

in machine code. You can try this yourself using the command debug from the command prompt.

Answer 3

Yes pretty much as above.

You can aslo think of langauges in terms of 'generations'

Machine code is 1GL (generation language) where you code in machine binary. Assembly was then a 2GL (2nd generation language) where its slightly more 'english' to program but still pretty low level.

A language such as c is 3GL and is more readable to the human eye but still requires a fairly low level knowledge.

Languages such as the database language sql is a 4GL as its pretty much in english (select 'columns' from 'table')