The more memory your computer has, the more programs you can run simultaneously, and the better performance you'll get from your computer. Increasing the amount of memory in your MacBook Air is an easy way to improve performance.
MacBook Air uses one of the fastest memory technologies available today - 1600MHz, Low-Power Double Data Rate 3 (LPDDR3), synchronous, dynamic, random-access memory (SDRAM) - ensuring that the Intel dual-core i5 or i7 processor is constantly fed with data without wasting clock cycles.
Every MacBook Air comes with 4GB of memory built into the system. If you feel you may need 8GB in the future, it is important to upgrade at the time of purchase, as RAM is not upgradeable in this model.