BootMedium

BootMedium refers to any storage device or medium that contains data used to initialize a computer's operating system or system firmware during the boot process. Common examples include USB flash drives, optical discs, internal or external hard drives, solid-state drives, and network-based resources used in PXE boot. The term is often used to distinguish bootable media from disk volumes that contain data only.

During boot, the system firmware (BIOS in older systems or UEFI in modern machines) identifies a boot medium, reads the initial boot sector (for BIOS) or the EFI System Partition (for UEFI), loads a bootloader, and transfers control to the operating system kernel or a live environment. Boot media may use different partition schemes, notably MBR or GPT, and may rely on specific boot efforts like an EFI boot entry or legacy MBR code.

Boot media are formatted to fit various purposes: optical media often use ISO 9660; USB or hard drives may carry ISO, IMG, or dedicated installer images; UEFI-enabled media place bootloaders in an EFI System Partition with .efi executables. Common use cases include operating system installation, system recovery, live operating systems for testing, firmware updates, and network boot via PXE.

Creation and testing of boot media are supported by dedicated tools such as Rufus and balenaEtcher for USB drives, and platform-specific utilities for ISO images.

Security considerations include Secure Boot, which may require signed bootloaders and kernels, and the risk of malware on removable media.

Related topics include boot drive, live USB, PXE, bootloader, and firmware updates.