The Yocto OS (Linux) doesn't appear in the Edison's drive when you connect it to the PC. Actually, the Edison's drive should remain empty so you shouldn't see anything when you connect the Edison to your PC.
The Edison's drive was used to copy the image files and flash the Edison with the Yocto image; however this method is no longer used. There have been new images and a new method to flash them. This method uses a software called Flash Tool Lite. With this software you can flash the latest Yocto image in the Edison without copying the files in the Edison's drive. I recommend you to check the following document for additional details: Flashing the Edison Module
I also recommend you to flash your Edison using the Flash Tool Lite. You can download it from the following site, under the Flash Tool Lite section: IoT - Intel® Edison Board Download | Intel® Developer Zone. The latest Yocto image can be downloaded from the following link: http://downloadmirror.intel.com/25028/eng/edison-image-ww25.5-15.zip