A Software evolves over time and changes according to the user expectations of a particular period. You can definitely point out the differences between Windows 98 and Windows 7. In this video from YouTube user ‘The Rasteri’ (Andrew Tait), you will be shown how the upgrade process in Microsoft Windows works. He starts by installing MS DOS 5, applying a colour scheme and installing some standard software that can run on the ancient OS, then he keeps upgrading from one OS to another till he finally reaches Windows 7. The best part is that the games and other primitive apps installed in DOS 5 are still present in Windows 7, although the color scheme changed starting from Windows XP. The entire video takes about 10 minutes to complete, but it should have taken Andrew over 10 hours! I recommend you take a look at this video.
Source: @jackschofield on Twitter.