Hard Disk Partitioning

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Changing your hard disk partitions can be frightening since it may data loss. Here’s what you need to know before you start. If you were to compile a list of your favorite rainy day activities, it’s a good bet that partitioning your hard disk wouldn’t be among them. If you’re like most persons—- novices and veterans alike—- the very idea of partitioning is terrifying. Once you delete a partition, there is no turning back, so you must be absolutely certain of what you’re doing before you begin. If you delete a partition, you not only delete all data in it but also render that part of your hard disk inaccessible to your operating system. So if your hard disk consists of only one partition, as the disks in most new computers do, the deleting the partition would mean that you couldn’t access your drive at all not even if you were to boot from your emergency floppy disk (you’ve made one right?).

 If you’ve made up your mind to modify your partitions, be sure to make a complete backup before you use any disk-partitioning utility. DOS and window ’95 include a small program called fdisk, which until a few years ago was the only readily available utility for creating and deleting partitions. To access the utility, type “fdisk” at the DOS prompt and press Enter. A small menu from which you can get all your partition information will pop up. Move around the menu to your heart’s content, but for safety’s sake you should avoid item 3, “delete partition of Logical DOS Drive.” FDISK runs you through several confirmations before deleting a partition, but why take the chance? On the other hand, item 1—“create DOS partition or Logical DOS Drive” —- tells you several things about your hard disk without destroying anything. You may even discover free space you never you had.

How partitions happen?

Taking a hard disk from its pristine, newly manufactured state to fully functional DOS or window ’95 storage area require three steps: physical formatting, partitioning, and logical formatting.

To understand what each step does, let’s take a brief look at how hard disks operate. Hard disks are mechanical devices consisting of several stacked platters (small, round metal disks treated to store magnetic charges on both side), a spindle around which the platters rotate (much like the center post on a record turntable), and read and write heads attached to the disks by a mechanical arm. The read and write heads allow magnetic charges to be stored on the disk (as bits) and retrieved from it. When you direct a program to load a file from the disk, the platters spin around the spindle and the read head moves back and forth over the platters until it locates the desired bits. Software in the hard disk and the hard disk controller then load the bits into the RAM. When you save data, your computer transfer a series of bits to the hard disk, recorded by the write heads as magnetic charges.

From the stand point of your computer, the hard disk is completely useless until it undergoes the formatting and partitioning stages. The first of these stages is physical or low-level formatting that in most cases is handled by the manufacture (order drivers and SCSI drivers have utilities that refresh low-level formats, but IDE drivers don’t). Low-level formatting essentially gives the disk its physical structure. It adds tracks, sector, and cylinders, terms with which you’re ever had the pleasure of installing a new hard disk. You can think of tracks as begin like the grooves on a long playing record, although tracks are laid out in separate concentric circles rather than one long continuous spiral like the grooves on an LP. Tracks are divided into sectors each of which can store a given amount of data, and each platter has its own tracks and sectors. A cylinder encompasses all platters comprising the corresponding tracks—that is, the tracks that are the same distance from the spindle –on each. To visualise cylinders think of a tall stacks of pancakes and a numbers of drinking glasses, each having a different diameter. Center a glass above the pancakes then push down right through the entire stake. Then do the same with each remaining glass. The vertical configurations you’ve produced are cylinders.

Once a hard disk has been physical formatted, it can be divides into physical regions called partitions. Each partition occupies a group of contiguous cylinders and with some operating systems (Linux, for example), you can specify precisely which cylinders you want each partition to occupy. To purpose behind partitioning is segment your hard disk, for organisation’s sake and also to let you run multiple operating system on a single computer. Each operating system works best (and sometimes solely) with its own file system, and only one file system can exist in a single partition. Under some file system, there’s third reason for multiple partitions—to cut down on wasted space. We’ll deal with all these reasons a little later in the article. Each with your partitions in place, the hard disk is still useless in your computer. To make each partition capable of storing information, it must be logically formatted. Where physical formatting gives you disk it’s physical structure, logical formatting (which is unrelated to physical formatting) provides a means of exchanging data with a operating system by giving the disk a logical structure, the file system. When you use the format command in DOS or the format menu item in window explorer, you are initiating a logical format of entire a disk or a hard disk.

File systems

 The sole purpose of logical formatting is to place a file system on the disk. Your operating system determines what file system is available to you; you rarely get a choice. The most common file system for machines driven by INTEL processors are: 

·  FAT (File Allocation Table) —– The standard files system for DOS and Windows. Because of its widespread use, FAT is also accessible by Linux, OS/2, Window NT, and other operating systems.

 ·VFST (Virtual File Allocation Table) —— a protected-mode version of the FAT file system, used by window’95. it is compatible with the FAT system, the main difference being support for long filenames.

 · NTFS (NT File System) —– Windows NT’s native file system. You can install Windows NT on a FAT partition, but NTFS is far more advanced, with batter security and reliability, faster file access, and very little wasted space.

 · HPFS (High Performance File System) —– OS/22’s native file system. As with NTFS, which evolved from HPFS, the security, reliability, speed, and efficiency are far superior to FAT’s.

 · FAT32 (32-bit File Allocation Table) —– included with window’95 ORS2, a version that is only available preinstalled by the system.manufacture.FAT32 gets rid of many FAT limitations. But so far, it can’t be accessed by anything other than window95 ORS2.

Partitions, and Partitions?

If you’ve played with fdisk at all, you’re probably familiar with primary, extended, and logical partitions. Primary and extended are major partition types and the total number you can have on your hard disk is limited. Note that these limitations have nothing to do with the operating system. They stem from a decision, made by drive and BIOS manufacture in the early years of hard disks, that four partitions should be enough for anyone (a bit like DOS’ 640k memory limit). The extended partition was developed in response to the need for the more than partitions. An extended partition can itself be divided into as many logical partitions as you wish; in a sense, the extended partition acts as a container for them. In a system with multiple operating system, it’s common to have a primary partition for each OS and an extended partition, subdivided into three or four logical partitions, for the OS you use more frequently.

 In the DOS/Windows’95/Windows NT world, drive letters are assigned according to partition type. When your computer boots, it checks the master boot record, which is usually on the first sector of the first disk, and read the partition table in the record. The partition table the computer how the disks are partitioned and the operating system assign letters accordingly. The designation A: and B: are reserved for the floppy disk drives and the active primary partition (only one can be active) on the first hard disk is assigned C: now the first primary partition on each additional hard disk gets the next letter in sequence. Once the primary partition on all hard disk have been assigned letters all logical partition on the first hard disk take their turn, followed by all logical partition on the second disk and so on. If you add a new hard disk to single-drive system that had volumes designed C: and D:. the new disk’s primary partition becomes D: and your old D: becomes E:. Note that the OS will assign letters only to partitions it recognizes, so DOS/Windows95 will ignore an NTFS partition.

Why more partitions?

Most new computers are shipped with a large (20GB or greater) hard disk with only one partition. This causes three potential problems. First, it makes it hard to organise program and data, because you end up filling the C: drive with so many directories that finding anything becomes difficult. Wouldn’t it makes more sense to have a partition for programs, another for data and downloads, a third for games, and so on? Second, if you want to install an additional OS and want to use the file system native to that OS, you’ll have to back up your entire hard disk, delete the existing partition and create a new ones, then reformat and reinstall the operating system, programs, and data from scratch. In other words, not likely the third problem might come as a surprise. Large FAT partitions waste disk space. That may not be seem logical —-one big building with multiple rooms seems more efficient than several smaller buildings —-but it’s true. The problem stems from the fact that FAT file system was developed in the days when the floppy disks ruled and hard disk were small, and it was never meant to scale onto today’s multi-GB drives. It’s extremely inefficient at storing files.

 Why? To put it simply, FAT divides its partitions into grouping of sector called clusters. That’s fine, expect that FAT also limits the number of clusters in a given a partition to just over 65,000. As a result, as the size of the partition grows, so does the size of each cluster. For partition fewer than 128 MB, for example, each cluster will be 2k in size while a partition between 1GB-2GB has a relatively huge cluster size of 32k. And it’s not as if you have a choice; that 32k cluster size is the minimum for a 1GB partition, again because of the limited number of clusters the partition can have. FAT allocates disk space to files using whole clusters, even though very few files are precise multiple of the cluster size. The data occupying a file’s last cluster may fill the cluster completely or it may be as little as a single byte. With an even distribution of file sizes, the average wasted space per file will be half a cluster. On a 127MB drive with 2k clusters, your CONFIG.SYSfile, typically about 0.5k in size, wastes 1.5k. The small file on a 1.2GB drive with 32k clusters wastes 31.5k. On that same 1.2GB drive, a 100k file occupies just over three 32k clusters, with the majority of fourth cluster remaining empty.


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