I use all 4 Windows versions of the 21st Century, XP, Vista, 7, and 8. I also use Linux (Ubuntu). Ultimately, I use XP, 7, and 8 because they're light, fast, and have a variety of software available to them (at risk of sounding like an advert here). Vista I use because I don't feel like upgrading, and its works quickly on my laptop, so I just go with it. I use my various computers for different things - XP - Spreadsheets, data storage/creation, classic gaming - I do a lot spreadsheeting that sometimes I don't like putting on Google Drive, so I put it on XP because I can do it quickly and easily, and its as so far safer for the spreadsheets to be there than stored on my laptops or my other desktop, since this little desktop is secluded in a corner of my room, away from my little brothers who might try and break it. Vista - Gaming. Not so much a unique use, but its one that I enjoy doing. I also use Vista for general internetting and the occasional 3D model. However, since its a laptop, I don't do as many things on it because of its limited hard drive capacity (RAM is perfectly fine, although quickly becoming out of date). I also use this one for school. Since its the 8th grade, I can't say I do much complex science on it, but I try from time to time to run something complex on it. 7 - 3D modeling is a big one on 7. Because its much faster than my Vista machine at starting-up and getting out to go, and it also has a much greater memory capacity than the laptop, I use it for 3D modeling in Blender. This is the only computer I can use effectively with Blender Cycles engine, mostly because it runs quite a bit faster using GPU render than CPU render. Here, I do the majority of my artwork, projects, and models. On occasion, I'll use it for gaming, but since I have the gaming laptop for that, I normally don't tend to. As far computer science goes, does website administration count? This is where I do the majority of that. 8 - Testing. I like testing, its fun, so I often try to test programs on my old laptop running Windows 8 Developer/Consumer preview. The developer preview inexplicably wound up never turning back on again, so I just installed the Consumer preview over it. It's a dual boot with Ubuntu, so I get the best of light and commercial software.