If you are preparing for CAT, then you would cover almost all the major topics that will be in any other kind of MBA exam whether it be XAT, CMAT, MAT or ATMA.
There might, however, be additions of certain sections in few exams. For instance, XAT also tests its candidates on decision making and conducts an essay writing in the end of the exam.
CMAT similarly, tests general awareness of the participating students.
Moreover, looking into the difficulty level, exams like CMAT, MAT and ATMA are considered to be comparatively easy than CAT as an aptitude exam in all its sections.
Exams like SNAP and NMAT are specifically conducted for Symbiosis Institutes and Narsee Monjee Institute of Management respectively and will hence,  consider the scores of their respective exams only.
To speak specifically about the exams that you asked :
*MAT: It's a 150 minute exam conducted both online as well as offline. It comprises of 5 sections :
1. Language Comprehension
2. Intelligence and Critical Reading
3. Data analysis and Sufficiency
4. Mathematical Skills
5. Indian and Global Environment
1 mark will be awarded for each right answer and each wrong answer brings a penalty of 0.25 mark.
Each section has 40 questions.

*XAT: The total duration of XAT exam is 3 hours 30 minutes. It comprises of two parts. Part 1 is of 170 minutes and part is of 30 minutes. XAT 2018 was conducted online.
Part 1 has three sections:
1. Decision making
2. Verbal and Logical ability
3. Quantitative ability and Data Interpretation
Part 2 has two sections:
1. General Knowledge
2. Essay writing
This exam follows +1,-.025 marking system. +1 for each correct answer and - 0.25 for each wrong answer.
Total part 1 had 74 MCQs, however it had been 72 at times too.
Part 2 has 25 GK questions and one essay writing topic.
These are few additional things that you need to prepare for.
All the best!!

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