Just as Microsoft blogger Paul Thurrott predicted one month ago, Microsoft is set to distribute copies of its Windows 10 operating system on USB thumb drives. The USBs are now available for pre-order on Amazon.com, Inc., and users can choose from both the Home and Pro editions of the OS.

Those interested should note the USBs aren’t the fastest way to get their hands on Windows 10. According to Amazon, the thumb drives won’t arrive until August 16, more than two weeks after Microsoft will begin rolling out the finished OS to beta testers and other users from July 29.

For now, Amazon.com is the only place where Microsoft is selling physical copies of Windows 10, VentureBeat reports. Neither Amazon’s biggest rival Best Buy, nor the Microsoft Store currently has the USB drives listed right now.

Buyers should beware that ordering a USB means paying for an upgrade that most existing Windows users can download for free. And the USBs don’t exactly come cheap, with Amazon listing them at the same price as a copy of Windows 8.1. Windows 10 Home will set buyers back $119, while the Windows 10 Pro edition is priced at $199.

Speaking to VentureBeat, Microsoft acknowledged users can buy Windows 10 on USB “in retail channels shortly after launch.”

It’s not exactly cheap but then again, the USB might be the only option in some instances, for example if you’re building a new computer out of various bits and there’s no existing OS to install, if you don’t have Internet access, or if you’re still running Windows XP.

Microsoft isn’t the first major vendor to distribute its OS through USBs. Apple did the same, selling USB sticks pre-loaded with its OS X Lion for Mac users. However, Apple notably also offers alternatives, including allowing users to create a bootable drive to upgrade their system, or simply pop into any Apple store and let the staff upgrade it for you.