"Follow-up on High DPI resolution
We don't have a way of knowing for sure why users adjust their screen resolution down, but many of the comments we’ve seen match our hypothesis that a lot of people do this to because they have difficulty reading default text on high resolutions displays. With that said, some users probably stumble into this configuration by accident; for example due to a mismatched display driver
or an application that changed the resolution for some reason but did not change it back. Regardless of why the screen resolution is lower, the result is blurry text that can significantly increase eye fatigue when reading on a PC screen for a long period of time. For LCD displays, much of the blurriness is caused by the fact that they are made up of fixed pixels. In non-native resolution settings, this means that the system must render fractional pixels across fixed units, causing a blurred effect. Another reason for the relative blurriness is that when the display is not set to native resolution, we can’t properly take advantage of our ClearType text rendering technology , which most people (though not all) prefer. It is interesting to note that the loss of fidelity due to changing screen resolution is less pronounced on a CRT display than on an LCD display largely because CRTs don’t have fixed pixels the way that LCDs do. However, because of the advantages in cost and size, and the popularity of the laptop PC, LCD displays are fast gaining market share in the installed base. Another problem with running in a non-native screen resolution is that many users inadvertently configure the display to a non-native aspect ratio as well. This results in an image that is both blurry and skewed! As you can imagine, this further exacerbates the issues with eye strain.
Looking beyond text, in these scenarios the resulting fidelity for media is significantly reduced as well. With the configuration that many users have, even if their hardware is capable, they are not able to see native “high def” 720p or 1080p TV content, which corresponds to 1280x720 and 1920x1080 screen resolutions respectively. The PC monitor has traditionally been the “high definition” display device, but without addressing this problem we would be at risk of trailing the TV industry in this distinction. While it is true that only about 10% of users have a truly 1080p capable PC screen today, as these displays continue to come down in price the installed base is likely to continue to grow. And you can bet that there will be another wave of even higher fidelity content in the future which users will want to take advantage of. As an example, when displays get to 400 DPI they will be almost indistinguishable from looking at printed text on paper. Even the current generation of eBook readers with a DPI of ~170 look very much like a piece of paper behind a piece of glass
From this we see that there is a real end user benefit to tap into here. It turns out that there is existing infrastructure in Windows called “High DPI” which can be used to address this. High DPI is not a new feature for Windows 7, but it was not until Vista that the OS user-interface made significant investments in support for high DPI (beyond the infrastructure present earlier). To try this out in Vista, rt. Click desktop -> personalize and select “Adjust Font Size (DPI)” from the left hand column. Our thinking for Windows 7 was that if we enable high DPI out of the box on capable displays, we will enable users to have a full-fidelity experience and also significantly reduce eye strain for on-screen reading. There is even infrastructure available to us to detect a display’s native DPI so we can do a better job of configuring default settings out of the box. However, doing this will also open up the door to expose some issues with applications which may not be fully compatible with high DPI configurations."
Read more at :- Engineering Windows 7 : Follow-up on High DPI resolution