The size of the default disk partitions were designed so that a default installation fits on the disk. The default disk layout is: root is on partition a, /usr is on partition g, the var area is a directory under /usr, and the swap area is on partition b. If you perform a default installation, you cannot preserve existing custom partition tables or disk labels. Custom partition tables are partition tables that have been changed to sizes other than the default values. If a customized partition table exists, it will be overwritten.