System partition and boot partition

The system partition and the boot partition are computing terms for disk partitions of a hard [disk drive] or solid-state drive that must exist and be properly configured for a computer to operate. There are two different definitions for these terms: the common definition and the Microsoft definition.

Common definition

In context of every operating system, except those developed by Microsoft, the system partition and the boot partition are defined as follows:

The boot partition is a primary partition that contains the boot loader, a piece of software responsible for booting the operating system. For example, in the standard Linux directory layout, boot files are mounted at /boot/. Despite Microsoft's radically different definition, System Information, a utility app included in Windows NT family of operating systems, refers to it as "boot device".
The system partition is the disk partition that contains the operating system folder, known as the system root. By default, in Linux, operating system files are mounted at /.

In Linux, a single partition can be both a boot and a system partition if both /boot/ and the root directory are in the same partition.

Microsoft definition

Since Windows NT 3.1, Microsoft has defined the terms as follows:

The system partition is a primary partition that contains the boot loader, a piece of software responsible for booting the operating system. This partition holds the boot sector and is marked active.
The boot partition is the disk partition that contains the operating system folder, known as the system root or %systemroot% in Windows NT.

Before Windows 7, the system and boot partitions were, by default, the same and were given the "C:" drive letter. Since Windows 7, however, Windows Setup creates, by default, a separate system partition that is not given an identifier and therefore is hidden. The boot partition is still given "C:" as its identifier. This configuration is suitable for running BitLocker, which requires a separate unencrypted system partition for booting. As of Windows 11, this nomenclature is still used by the "Disk Management" utility.