My father in law has a 3GB laptop running Vista. I'm wondering if he'll see a
significant performance increase with 10.
I installed Windows 10 on four computers - three desktops and one laptop. The installations were upgrades over Win 8.1 or Win 7. The desktop installations were essentially flawless. (I've been a Windows Insider and have been experimenting with Windows 10 builds since late 2014. Two of the desktops and the laptop did not recieve Windows 10 until the official release.)
The laptop is a six year-old + Toshiba with an AMD Turion 2-Core, an AMD X1300 discrete graphics card, 3GB of RAM, and a 7200 RPM hard drive. The laptop originally had Vista, which I had upgraded to 7 Pro. It now runs faster and smoother with 10 than it did with 7. It feels as if I just added a couple more years of practical usability to the laptop. Drivers installation and functionality was very good right after the installation, with the exception of the video card. The Windows generic driver, although newer than the AMD (ATI) driver, would not allow the monitor to scale to the full resolution available. I uninstalled the generic graphics driver and installed X1300 drivers I found on the Internet. All graphics functionality immediately returned to full performance.
A couple programs required re-installation in compatibility mode; and they now work perfectly. I may have had to install the X1300 drivers in compatibility as well. I don't remember.