What Microsoft places in the ESP
Microsoft places the HAL, loader, and other files that are needed to boot the operating system in the ESP.
ESP placement on the disk
The ESP should be first on the disk.
The primary benefit to placing the ESP first, is that it is impossible to span volumes when the ESP is logically between the
two data partitions that you are attempting to span.
System or device manufacturer additions to the ESP
The ESP should only include files that are required for booting an operating system, platform tools that run before
operating system boot, or files that must be accessed before operating system boot.
For example, files that are required for performing pre-boot system maintenance must be placed in the ESP.
Other value-add files or diagnostics used while the operating system is running should not be placed in the ESP.
It is important to note that the space in the ESP is a limited system resource;
its primary purpose is to provide storage for the files that are needed to boot the
operating system.
System manufacturer placement for files such as platform diagnostics or other value-added files
The preferred option is for system manufacturers to place value-add contents in an OEM-specific partition.
Just like MBR OEM partitions, the contents of GPT OEM (or other unrecognized) partitions are not exposed
(given drive letters or returned in volume lists).
Users are warned that deleting the partition can cause the system to fail to operate.
An OEM-specific partition should be placed before the MSR and after any ESP on the disk.
Although not architectural, this placement has the same benefits as placing the ESP first.
For example, it is also impossible to span volumes when an OEM-specific partition is logically between the two data
partitions that you are attempting to span.
Placement in the ESP is an option for applications or files that execute in the pre-operating system boot environment.
However, the ESP is architecturally shared space and represents a limited resource.
Consuming space in the ESP should be considered carefully.
Files that are not relevant to the pre-operating system boot environment should not be placed in the ESP.
