When you build your package with the pkgmk command, the command performs the calculations and actions necessary to organize a multiple volume package. A multiple volume package is called a segmented package.
However, you can use the optional part field in the prototype file to define which part you want an object to be located. A number in this field overrides the pkgmk command and forces the placement of the component into the part given in the field. Note that a one-to-one correspondence exists between parts and volumes for removable media formatted as file systems. If the volumes are preassigned by the developer, the pkgmk command issues an error if there is insufficient space on any volume.