What does the "open as portable device" option in Windows do?

Solution 1:

Use as a portable device means that programs or software run from the device will store their data on the portable device itself and should not require storage or reg changes on the machine which they are running.

Used a lot in the field of forensics where it is critical to access a system while causing minimal (or no) changes to the file system or OS on the target machine.

Solution 2:

WPD is a model which provides a way of interaction between computer and portable device plugged into it. Plugged devices publish services which application running on the computer can access. For example mobile device can expose service for synchronization of contacts on the device with the outlook (besides just browsing device internal storage). When you select "open as portable device" context menu option, explorer queries device for available services and shows them. Since your USB stick does not have (basically cannot have) any exposed services this option selection looks similar to a plain storage browsing.

Solution 3:

This uses the:

Portable Devices (WPD) Platform Enhancements

When accessing the USB stick more information can be found at:

Windows Portable Devices Team Blog > New Features for Windows 7

I hope this is helpful.