If you’re not recording, then the requirements are fairly minimal and can probably be met by any PC made within the last year or so. It needs to be running Windows 7, and needs both an ethernet connection and a USB-2 port (USB-3 will also work). My PC is several years old, but even so the app takes less than 120 meg of RAM and less than 10% of CPU time, according to the task manager. As your question implies, running the recording software demands faster hard drive performance, more memory, and more processing horsepower.
Your video card and monitor need to run with at least 1440×900 resolution in order to see the whole switcher panel; my machine runs 1680×1050, and looks good. Since the app is much wider than it is high, a widescreen display will probably be more useful.
If you’re thinking to buy an entirely new computer, you might consider an all-in-one with a touch-screen monitor; the switcher app looks like it would be pretty well suited to a touch screen.
During normal operation, the switcher control application communicates with the ATEM through the ethernet cable; if you are using the recording software, that also uses the USB connection. You also need the USB connection to initially set up the ATEM: to assign its IP address, and to perform firmware updates.
Hope this helps —
Jeff Hartman
Engineering Project Manager
Newport Television, Northeast