Some of the OS concepts
( memory, IO, Scheduling, process\Threads, multithreading )
[a good book "Modern Operating Systems, 2nd Edition, Andrew S. Tanenbaum"]
Basic knowledge of Computer networks
[a good book by Tanenbaum
OOPS concepts
Finite autometa
A programming language ( I learnt C first then C++)
Algorithms
( Time\space complexity, sort, search, trees, linked list, stack, queue )
[a good book Introduction to Algorithms]
