User Guide

Status flag of a partition on the first hard disk usually tells the default MBR
code that boot should be performed from this partition. Partition type
identifies it with a certain operating system. An operating system usually
recognizes only partitions with the numbers it knows and ignores the rest.
Such table structure has the following limitations:
• Maximum amount of partitions is four;
• Maximum number of types – 255;
• Maximum supported hard disk size is 4 terabytes.
The first limitation proved to be the most serious, so partition type 5 is now
used not for partition description but as a reference to the sector where another
partition table is located (let us call such partition table the extended partition
table). Thus it became possible to have an unlimited number of partitions on a
hard disk.
Partitions whose information is stored in MBR are called primary, while all
others are known logical partition. The point of such division is that many
operating systems can only be booted from a primary partition and only on
the first hard disk.
Most operating systems impose the following limitations on partition
structure of a hard disk:
• There can be only one primary partition for this operating system and it
is booted from it. All other primary partitions should be of types that are
not recognized by this OS;
• In the MBR partition table there can be only one reference to a partition
table and such extended partitions must include all the logical partitions
of this hard disk;
• Primary partitions should not overlap with the logical partition;
• Each extended partition table may hold only one usual partition and only
one reference to a partition table;
• Each partition table must be located in the first sector of a cylinder;
• Each subsequent table must be located further from the beginning of the
hard disk then the previous one;
• A partition that is described in an extended partition table must be
located right after it, usually at the beginning of the next track.
The limitation of only one reference to a usual partition and only one
reference to a partition table results in all logical partitions of a hard disk
forming a linear chain.
22 Chapter 2 : Basic Information