Windows 10 is coming on July 29, and it's going to be free for most home users of Windows 7 and 8.1 until July 2016. But while a legitimately free copy of Windows is pretty enticing, upgrading isn't the best move for everyone. You may recall that Windows Vista had some compatibility woes, largely due to how other software detected the version of the operating system. Depending on the vintage of your PC and how you use it, upgrading your OS may not be worth the potential trouble, even if the OS is free. Let's look at a couple scenarios where you might want (or not want) to take the plunge into Windows 10.

Scenario 1: You have a Windows XP-era PC

Officially, if you have a 1GHz CPU, 1GB of RAM, a video card that can handle DirectX 9, and 16GB of hard drive space, you can run the 32-bit version of Windows 10. But realistically, you want a CPU with multiple cores that runs much faster than that. If your PC dates from 2000 to mid-2006, then Windows 10 probably won't run very smoothly. A Pentium 4 may run up to 3.2GHz, but its single core will still struggle.

A good rule of thumb is whether or not you can stream an HD video smoothly on YouTube. It's not until you reach Intel's Core 2 Duo era that your options open up, and that didn't start until the summer of 2006. For AMD's part, Phenom II chips would be the entry point for a solid experience, and those didn't come out until February 2009. System RAM isn't as big of an issue, though. We've seen tablets at retail running Windows 8 with 2GB of RAM without a problem.

If you don't know what CPU you have, you can download a small, free program called Speccy that will tell you. Click the CPU section on the left-hand side for detailed technical info about your chip, including how many cores and threads it has. You can Google the CPU to find out when it came out. Speccy will also tell you how much system RAM you have. Remember, we'd recommend a multi-core CPU that's at least an Intel Core 2 Duo from 2006, or an AMD Phenom II chip from 2009 onward, and at least 4GB of system RAM if you want to do multitasking.

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1024 Mbytes equals 1GB, so this machine has 16GB of system RAM.

Scenario 2: You have a Windows Vista-era PC or a newer model

This phase goes from late 2006 onward. If your machine ran Vista fairly smoothly, it should be fine for running Windows 10. If anything, Windows 10 should run more smoothly than Vista, thanks to enhanced memory management. Test an HD YouTube video test at 1080p if you're not sure -- movie trailers are usually good for that. Microsoft has worked quite hard in recent years to make its OSes work efficiently with your system RAM and CPU cycles. Regardless, keep in mind that you must be running Windows 7 or 8.1 to qualify for the free upgrade to version 10. So if you're still running Vista or XP, you'll have to pay up.

On the other hand...

Even if your PC can run every operating system under the sun, you also have to consider what you use it for. And if you're happy with the job your PC is doing, then Windows 10 may not offer compelling new features.

If you're a gamer, we recommend upgrading, because only Windows 10 will have DirectX 12. Games that support DirectX 12 can take advantage of your PC's components to a degree that we haven't seen before, so you might be able to run at higher resolutions, enable more visual effects, or both, without having to install new gear.

But if you mainly use your PC for things like browsing the Internet, word processing, editing photos, and streaming media, Windows 10 is unlikely to change your world. And if you have Windows 7 or 8.1 installed right now, you have until July 2016 until the free upgrade offer expires. That's plenty of time to hang back and let the early adopters kick Windows 10's tires for you. Alternatively, you can try it out in a virtual machine, which doesn't require you to actually upgrade.

Is it time to just buy a new PC for Windows 10?

If you're in Scenario 1 and your PC doesn't do what you'd like it to, you have options, even on a tight budget. Right now, you can pick up an HP Stream 13 laptop for $230 (MSRP). It has a 13.3-inch HD screen, 2GB of RAM, a 32GB hard drive, a USB 3.0 port, integrated Wi-Fi and webcam, an HDMI port for plugging in an external monitor, a media card reader, and one year of Office 365. The productivity suite and the Windows 8.1 license it comes with would ordinarily cost you about $200 total, so that's a pretty good deal. Plus it's a laptop, so you can take it anywhere.

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The HP Stream is a low-cost PC that will be ready for Windows 10.

That kind of machine will be ready for Windows 10 when you decide to upgrade. If you prefer a desktop, companies like HP, Dell, and Lenovo have "outlet" websites that sell refurbished PCs (some of which were only taken out of the box and never actually used) for a fraction of the retail price.

More resources

Windows 10 in a nutshell

Windows 10 arrives on July 29

How to run Windows 10 on a virtual machine

Tom is the senior editor covering Windows at Download.com.