Customer Information - Desktop/Tower The label with the computer serial number is located on the large panel that is the right side when the computer is used as a tower, as shown in this graphic, or is the top panel when the computer is used as a desktop. A - Computer label - provides the serial number, model number, and support contact information. B - Microsoft® Certificate of Authenticity (COA) label - provides the product identification number for the Windows® operating system originally installed on the hard drive.