Boot discs explained: An overview of booting your PC from something other than your hard drive
Jsmithhere asked the Desktops forum about booting from CDs, DVDs, and flash drives.
When you boot your PC, it generally loads an operating system (such as Windows) from a hard drive or SSD. But you can bypass this process by booting from a specially-prepared CD, DVD, or flash drive.
Why would you do this? Perhaps Windows is so messed up that it fails to boot on its own. Or you want to scan for malware in a clean environment. Or perhaps you just want to play with another operating system without bothering to install it.
Before you can successfully boot from a disc or flash drive, you may need to go to your computer's Setup screen and change the boot order. How you do this varies with different computers. Look for an onscreen message, soon after you boot your PC, that says something like "Press key for setup."
The following terms and definitions will help you understand booting from media that doesn't stay inside your PC.
Boot disc: Any bootable CD or DVD. Although not technically accurate, the term is also used for bootable flash drives.
.iso file: A CD or DVD image file that you can download and burn to a disc. To burn one in Windows 7, simply double-click the file and follow the prompts. In Windows 8, right-click the file and select Burn disc image. For earlier versions of Windows, you'll need to install a third-party program such as the free ISO Recorder.
Universal USB Installer: A free program from Pendrivelinux.com that can prepare a bootable flash drive from an .iso file. This doesn't work with every .iso file in existence, but it supports an amazingly large selection of them.
Windows System Repair Disc: This Microsoft boot disc provides several tools for repairing a bad Windows installation. To create this disc in Windows 7, click Start, type system repair disc, and press ENTER. Windows 8 provides different options for a CD or a flash drive. For a CD, press WINKEY+R, type recdisc, and press ENTER. For a flash drive, press WINKEY+R, type control panel and press ENTER. Type the word recovery in the Search Control Panel field in the upper-right corner. Click Create a recovery drive.
Live Linux: This generic term refers to several versions of Linux that can be booted from a disc or flash drive. The most popular of these, and probably the most powerful, is Ubuntu.
Read the original forum discussion.