Hello Ravi,
SAT exam is of two types namely SAT and SAT subject tests. SAT exam pattern has three sections.
1. Evidence-Based Reading and Writing
Reading Test
Writing and Language Test

2. Math

3. Essay (optional)
The acceptance of the SAT score depends on the college/University. SAT subject tests are opted by the candidates whose colleges ask for the SAT subject tests score.
Go through the link below for details-

https://studyabroad.careers360.com/articles/sat

Good Luck!

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