Following right on the heels of Windows Vista SP1 RTM, Apple has seemingly one-upped Microsoft by releasing OS X 10.5.2 – the biggest update to OS X ever – effective immediately and available to all.

The release documentation for the OS X 10.5.2 build can be found at the Apple site, and it contains all the gory details about this whopping update. It’s 343 MiB (for comparison, Vista SP1 x86/x64 RTM are 434/726 MiB, but they contain plenty more changes) and contains a number of important fixes.

At the moment, you can download the update via OS X’s “Software Update” feature or directly from Apple’s OS X downloads site here. Updates are also available for OS X Server, the direct download link can be found here (382 MiB).

10.5.2 ships with several important security updates that were not previously disclosed/patched as well – if you don’t intend on updating to 10.5.2 anytime soon, you should definitely grab the standalone security update found here.