It's not Windows, it's an open-source project all its own, based on the Unix OS. The NIST people started the project on that OS because of its realtime capabilities, which Windows lacks. The project is now being developed by a loose coalition of programmers at linuxcnc.org. It will keep track of servo feedback loops and close them at the computer, but setting it up is not very easy, especially if you aren't familiar with the operating system.
It's hard to say what it would take to power your Bridgeport. Does it have ballscrews, or is it a manual model? If it's a manual J-head, you might want to keep it intact, and use it to make parts for a conversion of a mill that was built for CNC use. Machines with good iron and ballscrews but bad or obsolete controls come up frequently, often at scrap prices, and would save you a lot of time and money over converting a good manual machine.
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