Troubleshooting and Maintaining Your PC All-in-One For Dummies. Dan Gookin

stored in the PC’s battery-backed-up CMOS is the PC’s primary boot device. For nearly all PCs, that device is the main mass storage device, a hard drive or solid-state drive (SSD), from which the Windows operating system is loaded. That consistency is necessary, but it can be overridden.

      To temporarily start the PC from another boot device, choose the Change Boot Device or Boot Drive command from the startup options. You see a list, such as this one:

      1. SATA: PORT 3: HL-DT-ST DVDRAM GH24NSBO

      2. SATA: PORT 6G 0: WDC WD5000AAKX-08U PART 0: Boot Drive

      3. USB: SanDisk Ultra 1.26: PART 0: Boot Drive

      4. UEFI: USB: SanDisk Ultra 1.26: PART 0: OS Boot Loader

      5. LAN: IBA GE Slot 0 °C8 v1403

      Granted, the list of boot devices isn’t friendly. Devices are listed by their connection and type as read by the PC’s firmware. A nerd could decipher the details, but what you’re looking for is the word boot, which appears three times in the preceding list.

      For example, if you want to start the computer from a USB thumb drive, you might choose Option 3, which contains the words USB and SanDisk (a thumb drive manufacturer) and boot drive. This choice assumes that you’ve connected the thumb drive and, further, that it’s configured with an operating system or other bootable software.