As part of its recent Assassin's Creed 3 mega-media blowout-o-rama, Ubisoft has confirmed the delayed PC edition's system requirements. They're modest demands, but if your gaming PC isn't up to scratch (say, if you're still using Windows XP), you've got until November 20 to sort that out.
Here's the minimum spec, straight from the horse's mouth. Obviously, faster would be better.
Supported OS: Windows Vista (SP2) / Windows 7 (SP1) / Windows 8
Processor: 2.66 GHz Intel Core2 Duo E6700 or 3.00 GHz AMD Athlon 64 X2 6000+ or better recommended
RAM: 2 GB (4 GB recommended)
Video Card: 512 MB DirectX 9.0c-compliant with Shader Model 4.0 or higher (see supported list)*
Sound Card: DirectX 9.0c-compliant (5.1 surround sound recommended)
DVD-ROM: Dual-layer drive
Hard Drive Space: 17 GB
Peripherals Supported: Windows-compatible keyboard, mouse, optional controller (Xbox 360 Controller for Windows recommended)
Multiplayer: 256 kbps or faster broadband connection
Supported Video Cards at Time of Release:
AMD Radeon HD 3870 / 4000 / 5000 / 6000 / 7000 series or better
NVIDIA GeForce 8600 GT / 9 / 100 / 200 / 300 / 400 / 500 / 600 series or better
As for that mega-media blowout-o-rama, check out our previews of the single-player campaign and multiplayer, and our interview with lead writer Corey May. You may as well read our preview of the Vita side-game AC3: Liberation, while you're at it.