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Make the most of large drives with GPT and Linux

Jul 30, 2009, 23:04 (1 Talkback[s])
(Other stories by Roderick W. Smith)

[ Thanks to An Anonymous Reader for this link. ]

"The MBR partitioning system is a hodge-podge of data structure patches applied to overcome earlier limits. The MBR itself resides entirely on the first sector (512 bytes) of a hard disk. The first 440 bytes of the MBR are devoted to code: the boot loader. The BIOS reads this code and executes it when the computer boots.

"Following the code area, the MBR stores data on four partitions, known as primary partitions. Each partition is described in two ways: using cylinder/head/sector (CHS) notation and using logical block addressing (LBA) notation. The CHS notation is almost a historical footnote today, because it's a 24-bit number. This means that it's limited to describing 8GB-disk areas. The 32-bit LBA values permit 2TB sizes. This 2TB ceiling is not easily overcome; there simply aren't any unallocated fields left in the MBR that could be used to add more bits to the LBA addresses.

"In addition to the looming 2TB problem, the MBR presents other difficulties. Chief among these is the limitation of four primary partitions. To work around this limitation, it's possible to set aside one primary partition as a placeholder (known as an extended partition) to hold an arbitrary number of additional partitions, known as logical partitions. This is, however, an ugly workaround that creates its own problems, such as difficulties installing multiple operating systems when too many of them want too many primary partitions to themselves."

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