Microsoft KB Archive/896528

= Reinstalling Windows XP Home (Part 3): Creating partitions =

Article ID: 896528

Article Last Modified on 6/7/2006

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APPLIES TO


 * Microsoft Windows XP Home Edition

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SUMMARY
This article is Part 3 of the Reinstalling Windows XP Home guide. This part explains how to create partitions.

To view the other topics of the Reinstalling Windows XP Home guide, see the Microsoft Knowledge Base articles that are listed in the &quot;References&quot; section.

The Reinstalling Windows XP Home guide includes the following topics: Part 1: Introduction Part 2: Preparing Windows XP for reinstallation Part 3: Creating partitions Part 4: Installing Windows Part 5: Post-installing devices Part 6: Configuring the work environment Part 7: Running Windows Update



MORE INFORMATION
If you reinstall the operating system, you will probably want to install it to a clean hard disk. You may also want to partition it more appropriately than before. The Windows PARTDISK and FORMAT hard disk programs let you do this. You can use these programs during Windows installation.

Hard disks can contain more than one partition. This means that the hard disk can be partitioned into several drives, so that your computer appears to have multiple hard disks. For example, the hard disk may already contain a drive C and a drive D. Partitioning offers several advantages. Some advantages are as follows:
 * You can make better use of available disk space, depending on the size of the hard disk and the file system that is used.
 * You can clearly separate the operating system, the programs, the personal files, and the backups or the images into different partitions. Besides simplifying data backup, this makes it easier to subsequently reinstall the operating system.
 * You can run several operating systems on a single hard disk without them interfering with or influencing each other.
 * You can manage multiple file systems. This lets you exchange data between the different systems.

Configure the hard disk
A hard disk consists of several platters called discs that are coated on both sides, top and bottom, with magnetic material. Each platter has a read/write head which moves across the platter to a position where it can read or store data. All data is recorded in concentric circles. Each circle is called a track.

The hard disk is also divided into pie-shaped wedges that intersect the tracks to create sectors. Each sector usually holds 512 bytes.

A track that cuts across all platters is called a cylinder.



On early hard disks, each track had the same number of sectors. This was not a problem because, at first, hard disks had limited disk space. Increasing the track sizes meant that lots of space was wasted because the outer cylinders were much larger than the inner ones. Nowadays, it is common practice to partition a hard disk into several zones, in which case the outer tracks contain more sectors than the inner tracks. This is known as Zone Bit Recording (ZBR).

CHS and LBA formats
Cylinders (tracks), heads, and sectors play a central role in hard disk management. Cylinder-head-sector (CHS) values can be used to address each part of the hard disk individually. Values are assigned from the outer tracks inwards, starting at 0 for cylinders, at 0 for heads, and at 1 for sectors. In the past, the values indicated the actual physical position of the sector on the hard disk. Later, logical CHS entries were used to represent the total hard disk space.

The CHS format can only be used to address hard disks that are no larger than approximately 7.844 GB. This is true because of the following restrictions:
 * The number of cylinders is restricted to 0–1023 (10 bits)
 * The number of heads is restricted to 0–254 (8 bits)
 * The number of sectors is restricted to 1–63 (6 bits)

This means that the maximum capacity is equal to 1024 cylinders × 255 heads × 63 sectors × 512 bytes per sector, or approximately 7.844 GB.

To circumvent this limitation, CHS addressing was enhanced with Logical Block Addressing (LBA). LBA groups cylinders, heads, and sectors into logical blocks and assigns block numbers starting at 0. This makes it possible to address all conventional hard disks.

Note The BIOS has a corresponding extension that is called &quot;INT 13h extensions.&quot; This extension provides a means to address hard disks larger than 8 GB.

File systems
File systems organize and manage hard disk space. They enable you to create folders and files and to find them again. They are also used to grant or to block access to files. Windows file systems do not operate directly with sectors. They work with clusters. A cluster groups multiple sectors into a single data storage unit for ease of management. Clusters also specify how much hard disk space is allocated to each file. Each file requires a whole cluster, even if it does not use all the available space.

FAT16 file system
Because it is an early system, the FAT16 file system can only manage 2 to the 16th power, or 65,536 clusters. Therefore, even very small partitions have very large clusters.



FAT32 and NTFS file systems
As hard disk capacities increased, the number of possible clusters also increased. Theoretically, the FAT32 file system is designed for 2 to the 28th power of clusters, and the NTFS file system is designed for 2 to the 64th power of clusters. These file systems allow for significantly larger partitions. They also make better use of data storage.





The master boot record
If you want to divide the hard disk into multiple partitions, there must be a specific location on the hard disk for storing the exact position of these partitions. This location is track 0, head 0, sector 1. It is the location of the master boot record (MBR) on every hard disk. The MBR consists of the following:
 * The master boot routine that is run when the computer is started
 * The partition table that contains the information about the partitions
 * The MBR identification code that identifies the MBR as a master boot record



Types of partitions
Because the MBR can only hold 512 bytes, the partition table is limited to four entries. This limited the number of partitions you were able to create. However, as drive capacity grew, the need for more than four entries became obvious. Because the partition table could not be expanded to include additional entries, one of the four partitions was subdivided into additional partitions. There are now three types of drive partitions:
 * Primary partition
 * Extended partition
 * Logical drive

Primary partition
A primary partition can be directly addressed as a drive and cannot be additionally partitioned. The operating system is usually installed on a primary partition. The operating system can therefore start from an active partition.

The boot procedure for the computer involves several steps that occur in the following sequence:
 * 1) The BIOS runs the power-on self test (POST).
 * 2) The BIOS looks for the starting device. This is usually the hard disk.
 * 3) The BIOS loads the MBR when it starts from the hard disk.
 * 4) The MBR determines the active partition.
 * 5) The MBR loads the boot sector from the active partition.
 * 6) The boot sector initializes loading of the operating system.



Extended partition and logical drive
An extended partition cannot be addressed directly as a drive. It is just a container. An extended partition enables you to incorporate logical drives. Individual partition tables instead of the MBR manage these logical drives. These tables are also named EBRs (Extended Boot Records), and they are based on the MBR. The most notable feature of EBRs is that they are interlinked like a chain. This means that the number of logical drives is not limited by the capacity of the partition table, but by the number of free drive letters.

Possible partitions
The hard disk can be partitioned as follows:
 * One primary partition
 * One primary partition and one extended partition with logical drives
 * Two primary partitions and one extended partition with logical drives
 * Three primary partitions and one extended partition with logical drives
 * Four primary partitions
 * One extended partition with logical drives for a hard disk that cannot be used for the boot procedure.



Partition the hard disk during system installation
During system installation, you can use the Windows installation CD to assign one primary partition and one extended partition with logical drives. Before you reorganize the hard disk, you must first delete existing partitions.

Caution This will delete all data on the hard disk.

Create appropriate partitions
Before you start, you should decide exactly how many partitions you want to create. In doing this, you should consider which tasks your computer must perform:
 * Which programs are you installing? Should they be installed in a single partition with the Windows operating system or in a separate partition?
 * How much data do you have? Would it be useful to separate data that is archived or that is used infrequently from data that you constantly process?
 * Do you frequently use files temporarily and then delete them?
 * Do you download lots of data from the Internet?
 * Do you use disk imaging software to back up specific configurations or databases?

Depending on how you answer these questions, there are several possible solutions:

Solution 1


Solution 1 is the minimal solution. The operating system is simple to reinstall without data being affected, such as with an update.

Solution 2


Solution 2 simplifies data backup. Archive data is no longer changed and does not have to be backed up continuously.

Solution 3


Solution 3 also simplifies data backup. The operating system and data can be backed up separately in image files.

Solution 4


Solution 4 is a good solution if you want to store Web sites, tools, and so on, temporarily. Then you can periodically format the download partition.

Note To install multiple operating systems on a single hard disk typically requires more than one primary partition. In this case, it is sufficient to create a primary partition for the Windows installation and to leave the rest of the hard disk free. You can then use Disk Management to create the other partitions.

Format the hard disk using the installation CD
You can also format the hard disk and not create partitions at this point. The drive partitions will remain the same, but you will start with a clean hard disk that you can reconfigure. Most likely, you will only have to format drive C, because you are only replacing the operating system. Other drives, if any exist, can remain as they are. If you only format the partition that contains the operating system, this could save you lots of work.

