Best simple Book - understanding low level aspects of programing

Any advice ?

Bits , Bytes , Hex , binary , memory etc.

Cheers

For low level programming (directly related to hardware) you probably need a book on Assembly.
This language depends heavily on the machine characteristics.
Or maybe a book on good old C? "The C Programming Language" Kerningham, Richie (maybe I mispelled the names) if I remember well...

One good (and free via the internet) source of info is Randall Hyde's Art of Assembly Language Programming.

Start with the 16 Bit Dos version, as it goes more in depth on memory and bits and bytes, and numbering systems, etc.

You can find the online version of these books here:
Art of Assembly Language Programming and HLA by Randall Hyde

I generally agree with the other comments. If you are looking for something really basic, then consider "Code" by Charles Petzold. It is somewhat long-winded, and experienced computer people may get bored with it. However, it may be good for beginners as it does not assume any prior knowledge of anything.