Apple has just issued OS X version 10.8.5, the fifth major update that Mountain Lion has received since it was released last July. It's no Mavericks, but as usual the update includes a lengthy list of fixes and security updates that you'll want to apply to any Mac running 10.8. You can grab the Combo updater from Apple's support page here or download the update automatically through the App Store's software update page.

One of the fixes included in the update is meant to remedy a problem we had with the 2013 MacBook Air. It was one of the first high-end laptops to ship with support for the faster 802.11ac Wi-Fi standard, but our testing found that the improvements over the 802.11n adapter in the 2012 model just weren't as large as they should have been. Additional testing in Windows 8 confirmed that there was no problem with the hardware—for whatever reason, file transfers under OS X were less than one-third of the speed they were in Windows 8. 10.8.5 allegedly fixes this issue, so I broke out my 2013 MacBook Air to see what kind of improvements we can actually expect.

Our network configuration remains the same as it was in our original testing: we're copying a single large file from a 2012 Mac mini to a 2013 MacBook Air using the AFP and SMB protocols. The Mac mini is connected directly to our 802.11ac AirPort Extreme Base Station via gigabit Ethernet, while the Air is connected to the AirPort via 802.11ac. The laptop is about ten feet from the router, and there is a clear line of sight between the two. We tested under 10.8.4 and 10.8.5 using both the AFP and SMB protocols (AFP is said to be fixed in the 10.8.5 release notes; SMB is not mentioned).

That's more like it! When transferring files over the AFP protocol, it looks like OS X now performs more-or-less identically to Windows 8. Performance is well over double where it was in 10.8.4, which bodes well not just for the 2013 MacBook Air but for any other 802.11ac Macs that come out in the future. Transfer speeds over SMB haven't changed, unfortunately, but we wouldn't read too much into that—Apple is due to replace the Mountain Lion SMB implementation with a new SMB2-based protocol in Mavericks. While we haven't been able to test the latest OS X 10.9 developer betas, we're confident that Apple will have ironed out any issues by release, since the company is clearly aware of the problem.

One thing to note if, like me, you're using an OS X computer as your file server: I didn't get these increased file transfer speeds until I had updated both the MacBook Air and the Mac mini to 10.8.5. If you're using an NAS device or a Windows box as a file server, this probably won't be something you have to worry about, but it's worth noting for all-Mac setups.

Other fixes that are found in the 10.8.5 update include fixes to: an issue that prevents Mail.app from displaying images, an issue that prevents the screensaver from starting automatically, Xsan reliability fixes, more reliable large file transfers over Ethernet, authentication performance for Open Directory servers, smart card authentication issues, as well as the issues fixed in the 2013 MacBook Air Software Update 1.0.

There are also several security patches, which are also available via separate updates for Snow Leopard, Snow Leopard Server, Lion, and Lion Server.