Not all the new MacBook Airs are created equal. TLDToday discovered that Apple is yet again using two different manufacturers for the Air's SSD drives. Some MacBook Airs are shipping with Samsung SSDs, while others are shipping with SSDs made by Toshiba. The issue that arises with this is that the Samsung SSDs are faster than the Toshiba ones.
TLDToday found that the MacBook Air with a 128 GB Samsung SSD produced speeds of up to 246 MB/s write and 264 MB/s read. On paper that's a lot faster than the 156 MB/s write and 208 MB/s read speeds that the 128 GB Toshiba SSD-equipped MacBook Air achieved.
To find out which SSD your newest MacBook Air has go to the Apple menu and select About This Mac. Click the More Info button, then click System Report. Select Serial-ATA from the Hardware header in the source list. Look for where it says "Apple SSD." If the letters after that are "SM" you have the Samsung SSD. If the letters are "TS" you have the Toshiba SSD.
Unfortunately there's no way to check which SSD drive you have before buying the Air, unless the Apple store lets you open the box and power it on before you buy it. However, even if you have the Toshiba SSD, you aren't likely to see a real-world difference in the speed of your Air. Normal everyday tasks will run just as fast on the ultra-slim laptops no matter which SSD you have.