Top 6 reasons for not using old hardware when upgrading your OS
In general, new operating systems require heftier hardware than their predecessors. A system that runs the old OS just fine may run the new one very slowly or not at all, so be sure to check out the hardware requirements before you do the upgrade. You might need a faster processor and you almost always need more memory. Other components might need to be upgraded, too.
Setup errors and freezes
Probably the worst-case scenario is when the setup process fails in the middle of an upgrade. This can leave you with a non-working computer as neither the old operating system nor the new one may be usable. A possible cause is insufficient disk space but not the only cause.
Driver problems are one of the most common causes of all sorts of trouble connected with an OS upgrade. It is possible that you may be able to get through the installation process and the OS may run, however you may later encounter issues. For example, you may find that your sound card no longer works or that you can't print. That's usually a driver issue.
Another common thing that goes wrong when upgrading an OS is that you're no longer able to run some applications.
The operating system and applications can be reinstalled, but data is often unique and you might not ever be able to re-create it. Upgrading your operating system should leave your data intact, however this is not always the case.
It's best, as a matter of course, to store user data on a different partition from the one on which the operating system is installed. Wherever you store it, make sure it's backed up regularly, especially just before you perform an upgrade of the OS.
After upgrading to a new OS you may discover that the new OS runs much more slowly than the old one did. Typically this is caused by one of the five items discussed above.