What's the life span these days of a desktop PC these days? 5 to 7 years? How often does everyone replace their PCs?
I replace mine when newer software doesn't run properly, 5 years is about right. A few years ago I bought an off-the-shelf $500.00 Acer from Best Buy and replaced Vista with Linux. A few weeks ago I replaced that desktop with another $500.00 Acer from Best Buy because it couldn't run Ubuntu Mate 15.10 smoothly, the monitor would flicker.
desktops tend to last me quite some time. generally they have lasted until they are obsolete and tossed. I don't do any gaming and run only two monitors at once (or less). laptops, on the other hand, have tended to last about 4-5 years of heavy use before the blue screen of death. they have all been HP laptops. one thing about HP laptops is the corner edge tends to crack open. every one has done this so far.
Although I have much more recent PCs running automation, I still use 1986 Compaq 286, upgraded HD and it still runs longer term Commodities system. On PCs I keep them two years but laptops eleven months, batteries usually shot by then.
Windows 10 is 30% faster than windows 7 so an old PC can last longer these days if upgraded. A cheap SSD to replace the HD and windows 10 should get a few more years out of anything.
Eleven months for batteries? what on earth do you do with them? Also, batteries are easily replaced, there is absolutely no need to throw out the whole computer.
Desktop PC. Assuming you want something to use for trading which doesn't limit you, I went for a gaming PC, 64 GB RAM, SSD and quiet operation (can adjust fans with buttons on the case). There were some trouble with gfx card which had to be replaced, but it's been smooth operations since then. Running Linux, so BSOD or forced upgrade-cycles are moot. The OS and much of the software is free, and can always be reinstalled. Can recommend Linux Mint to get started quickly. This works for everything for me, but I'm not daytrading and only playing longer term trades. So while I'm waiting for analysis to complete, I often play online games on Steam, to chill out. Of course your needs might be different, but today, there's no need to switch desktop PCs until after 5-10 years, if you're lucky. If HDD fails, just buy a new SSD, since of course you have proper backups. Everything becomes cheaper in time. You'll need to blow off dust every few years and keep an eye on the fans, but other than that, there's no reason a real PC can't last 10-20 years, though you might get unlucky and need a replacement before that. If you buy proprietary garbage, of course, it will stop working and limit you. However, besides HDD, fans, powersupply and proprietary software, PCs are actually pretty resilient. Buying new PCs today doesn't really buy you much in terms of upgraded performance, and it makes sense to limit waste.
For trading, you normally don't need much in the way of power or graphic capability. If you want longevity and bang for your buck, suggest buying used workstations from Dell, HP, or Lenovo. My Dells have been virtually trouble free even when 10+ years old. (Haven't tried to use until "the wheels fell off". Hoping to run my current batch of T3500s at least until support for W7 ends. By then, they will be 11 years in service.)
I have 2 Dell Dimension 9150 desktops that I've being using for trading for 10 years. They still run like new!! I've been using a Fujitsu laptop every day for 8 years. Other than the fan being noisy it still runs fine. I do a disk clean up, disk defrag, check disk, and virus scans etc. every week. Maybe that's why they've lasted so long.