As you have asked about the difference between GMAT and GRE, it is hard to tell any but I am giving you some points to consider it

GRE:
Why Take It: The test is essential for admission to most graduate schools and a growing number of business schools.
Test Structure: The GRE consists of a 60-minute Analytical Writing section - with two essays at 30 minutes each. There is a Verbal Reasoning section, also with two 30-minute parts.

There are two 35-minute Quantitative Reasoning sections. There's also a 30-35 minute experimental section that can be either math or verbal.
Test Format: Offered as a computer adaptive by section exam
How It's Scored: Verbal and Quantitative scores from 130 to 170 in 1-point increments
Cost: $195
Testing Time: 3.5 hours using paper or 3.75 hours using computer
Scores Validity: 5 years

GMAT:
Why Take It: The test is essential for admission to most business schools.
Test Structure: The GMAT consists of a 30-minute Analytic section with one essay, a 30-minute Integrated Reasoning section, a 75-minute Quantitative section and a 75- minute Verbal section.
Test Format: The GMAT is a computer-adaptive test.
How It's Scored: The overall, or composite, GMAT score ranges from 200 to 800 in 10-point increments.
Cost: $250
Testing Time: 3.5 hours
Scores Validity: 5 years