Ondrej Holzman One of the biggest news at WWDC introduced MacBook Air was the presence of a new wireless connection standard – Wi-Fi 802.11ac. It uses the 2,4GHz and 5GHz bands at the same time, but it was found that the current OS X Mountain Lion does not allow to reach the highest possible speeds.
In his testing of the latest 13-inch MacBook Air to this finding matured Anand Lai Shimpi of AnandTech. A software problem in OS X Mountain Lion prevents the highest file transfer speeds on the 802.11ac protocol.
In the iPerf test tool, the speed reached up to 533 Mbit/s, but in real use Shimpi hit a maximum speed of 21,2 MB/s or 169,6 Mbit/s. Switching routers around, turning off all wireless devices in range, trying different ethernet cables and other Macs or PCs didn't help either.
Ultimately, Shimpi narrowed the problem down to two network communication protocols—Apple Filling Protocol (AFP) and Microsoft's Server Message Block (SMB). Further research then showed that OS X does not divide the stream of bytes into correctly sized segments, and therefore the performance of the new 802.11ac protocol is limited.
"The bad news is that the new MacBook Air is capable of amazing transfer speeds via 802.11ac, but you won't get them when transferring files between a Mac and a PC," writes Shimpi. “The good news is that this problem is purely software. I've already passed on my findings to Apple, and I'm guessing there should be a software update to fix this issue.”
The server also explored the capabilities of the new MacBook Air Ars Technicawhich he claims, that this 802.11ac machine running Windows 8 in Boot Camp achieves significantly higher transfer speeds than Apple's operating system. That Microsoft has slightly faster transfer speeds would not be such a surprise given the focus on the corporate sphere, but the differences are far too large to be explained by network optimization alone. Windows are roughly 10 percent faster over Gigabit Ethernet, 44 percent faster over 802.11na, and even 118 percent faster over 802.11ac.
However, this is the first Apple product with the new wireless protocol, so we can expect a fix. In addition, the problem also appeared in the Developer Preview of the new OS X Mavericks, which means that the speed limitation in OS X Mountain Lion is not intentional.
