In this day of age, it's very practical to have a Windows 7 installation on your USB key, for many netbooks and devices don't come with CD/DVD drives anymore.
If on your Windows 7 computer opening programs, saving documents, browsing the Internet and other every day tasks are getting slower, this is how you speed up things without installing an additional program.
Zip files are compressed archives containing documents, images, folders, basically any type of files on your computer. We create them to save space and make them more practical for sending via email or file sharing services.