Hello Johal, 

The good reference books are:

• THEORY OF COMPUTAION (TOC) - ULLMAN

COMPILER DESIGN - DRAGON , RAVI SETHI OR ULLMAN

DIGITAL AND ANALOG - R.P JAIN , MARRIS MANO

COMPUTER NETWORK - FOROUZAM , tanenbaum

OPERATING SYSTEM - GALVIN , TANELA

DBMS - NAVATHE (old edition )

ALGORITHM - CORMEN

DS AND PROGRAMMING - DENNIS RITCHIE

Study topics as per gate syllabus (or your interest) ,no need to read every page of each book.

Discrete Maths - kenneth rosen. (Group theory topic is missing in this)

Algorithms - CLRS

Data structure- Google topics with you are not good at. AVL ,Heap etc are important. Refer CLRS for them or many online links are available.

OS - Galvin

DCS - Morris mano or any other book will also do. K-map and gates are impotant.

DBMS - Korth for Transaction and concurrency control. Navathe for Functional Dependency and Normalization.

CN - Forouzan and refer sample video lectures on YouTube by Ranvindra babu ravula sir for problem solving

TOC - Peter linz. Regular language and DFA part is most important.

CC - the Dragon book, if you really have that much time and courage to read it. Else search for sample video lectures on YouTube by Ranvindra babu ravula sir for parsing.

CO-carl hamacher.

Madeeasy notes are available online download these if your mode of preparation is self study so that you can cross check from these that you have completed all the topics from each subject.

Hope it helped you!!

Thank you

You can follow the McGraw Hills series.