Default File Explorer Size and Position in Windows

You must install guest additions. In the "Devices" menu in the virtual machine's menu bar, VirtualBox has a handy menu item named "Install guest additions", which mounts the Guest Additions ISO file inside your virtual machine. A Windows guest should then automatically start the Guest Additions installer, which installs the Guest Additions into your Windows guest. After that your virtual OS scren will be automatically change resolution to fill entire screen.

Generically speaking: pixel = dot = point. They are different physical elements, depending on the medium you're working in. On computer monitors, pixels matter. In printing, dots are what count. Points are more generic and could refer to pixels or dots. The terms are commonly interchanged and often confused.

"Resolution" is the total number of [pixels, points or dots] wide, by total number of [pixels, points or dots] high. So a printer could have a resolution of 1200x1200 dots per inch, while a monitor could have a resolution of 1280x1024.

DPI and PPI are simply ratios. DPI is "dots per inch," PPI is "points per inch" or "pixels per inch." Those ratios increase and decrease based on the resolution (width x height, in pixels) and size (in inches) of a given medium.

To calculate the DPI, you need to determine the actual physical widths and heights of the medium. A common example is the Apple iPhone 4 screen:

Physical Width = 1.94 inches Physical Height = 2.91 inches

Width (in pixels) = 640 Height (in pixels) = 960

The assumption is that all pixels, dots, or points occupy a square space. Therefore, the simple equation to determine PPI / DPI is to divide pixel height by physical height, yielding roughly 329 DPI.

This information helps to answer your question. Windows does not have any idea what the DPI of your display is, because it has no concept of what the physical dimensions of the display are. You can buy 20" monitors with 1920x1080 resolution, as well as 70" monitors with the same 1920x1080 resolution. Both have signficantly different DPI's, yet Windows has no idea and nothing to do with it.

While Windows offers the option of increasing or decreasing the DPI, all it will really do is adjust system font sizes and default icon / UI sizes of things. Many other apps, graphics, websites and emails will actually get very poorly distorted if you make changes to the DPI settings.

Apple Mac OS (especially iOS) has significantly better support for DPI, and knows, based on the devices it is installed on, which DPI setting to use.