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You can partition a hard drive to store more than one operating system (OS). Store one OS in one partition and create a second partition for another OS. Granted, most people use only one OS, but if you want the option to boot to Windows or Linux, partitions are the key.

Essentials

Windows 2000/XP and Windows Vista/7 support two different partitioning methods: the older but more universal master boot record (MBR) partitioning scheme and the newer (but proprietary to Microsoft) dynamic storage partitioning scheme. Microsoft calls a hard drive that uses the MBR partitioning scheme a basic disk and a drive using the dynamic storage partitioning scheme a dynamic disk. A single Windows system with two hard drives may have one of the drives partitioned as a basic disk and the other as a dynamic disk, and the system will run perfectly well. The bottom line? You get to learn about two totally different types of partitioning. Yay! Given that basic disks are much older, we’ll start there.

Basic Disks

Basic disk partitioning creates two very small data structures on a drive, the MBR and a partition table, and stores them on the first sector of the hard drive—called the boot sector. The MBR is nothing more than a tiny bit of code that takes control of the boot process from the system BIOS. When the computer boots to a hard drive, the BIOS automatically looks for MBR code on the boot sector. The MBR has only one job: to look in the partition table for a partition with a valid operating system (Figure 12-1).

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NOTE Only one MBR and one partition table exist per basic disk.

Figure 12-1 Functions of the MBR and partition table

All basic disk partition tables support up to four partitions. The partition table supports two types of partitions: primary partitions and extended partitions. Primary partitions are designed to support bootable operating systems. Extended partitions are not bootable. A single basic disk may have up to three primary partitions and one extended partition. If you do not have an extended partition, you may have up to four primary partitions.

Each partition must have some unique identifier so users can recognize it as an individual partition. Microsoft operating systems (DOS and Windows) traditionally assign primary partitions a drive letter from C: to Z:. Extended partitions do not get drive letters.

After you create an extended partition, you must create logical drives within that extended partition. A logical drive traditionally gets a drive letter from D: to Z:. (The drive letter C: is always reserved for the first primary partition in a Windows PC.)

Windows 2000/XP and Windows Vista/7 partitions are not limited to drive letters. With the exception of the partition that stores the boot files for Windows (which will always be C:), any other primary partitions or logical drives may get either a drive letter or a folder on a primary partition. You’ll see how all of this works later in this chapter.

If a primary partition is a bootable partition, why does a basic drive’s partition table support up to four primary partitions? Remember when I said that partitioning allows multiple operating systems? This is how it works. You can install up to four different operating systems, each OS installed on its own primary partition, and boot to your choice each time you fire up the computer.

Every primary partition on a single drive has a special setting called active stored in the partition table. This setting is either on or off on each primary partition, determining which is the active partition. At boot, the MBR uses the active setting in the partition table to determine which primary partition to choose to try to load an OS. Only one partition at a time can be the active partition, because you can run only one OS at a time (see Figure 12-2). This restriction refers to a single drive, by the way. You can have active partitions on more than one physical drive; the settings in CMOS will dictate which