GPT disks can have the following types of partitions:
Logical Disk Manager (LDM) Metadata partition
LDM Data partition
OEM or Unknown partition
Each of these partition types is used and managed in a different way.
An Itanium-based computer must have one GPT disk that contains an ESP. This partition is similar to the system volume on an x86-based computer in that it contains the files that are required to start the operating system. Windows Server 2003 creates the ESP during setup and formats it by using FAT. The partition is sized so that it is at least 100 MB in size or 1 percent of the disk up to a maximum size of 1000 MB.
The ESP is shown in Disk Management but isn't ...