Since Windows 7 we have been blessed with a folder called WinSxS (“C:\Windows\WinSxS\”) – a repository for all applied service to Windows.
This folder must reside on the “c:” drive and grows over time – grows quite a lot in fact. Bear this in mind when thinking of new Laptops & Notebooks fitted with SSD or eMMC drives as solid state/flash drives tend to be of a smaller capacity than HDDs and with entry-level, ultra-thin, ultra-lightweight notebooks I recently discovered that they can have an initial, usable capacity as low as 20Gb. By the time Win 7 or 8, or 8.1 has been installed and updated there can be very little space left.
Now factor in the offer of an upgrade to Windows 10 and if the owner fails to read the requirements for Windows 10, any attempt to upgrade will fail because of this lack of space.
In one case, post such an attempt (so I am not sure what, if any, Windows 10 code has remained in the WinSxS folder, but the disk free space reduced a little further!) there was so little space left on the disk that another couple of service updates would probably have brought the PC to it’s knees!
SO – before you buy a lightweight notebook or laptop (with the probable exception of Chromebooks as the OS is geared for the smaller sizes) make sure you have enough disk space to make the system usable, and especially if you wish to upgrade to Windows 10!
NB. There area number of threads on the Internet about reducing the size of WinSxS – read them carefully before diving in and causing yourself more problems.