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Disk Managers
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Disk Managers
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Contents:
A Hard Disk is a mechanical, magnetic device used to store and retrieve data on Computers. Data is stored on the Hard Disk in the form of magnetic ‘patterns’. These patterns do not fade away for many years, thus affording a safe method to permanently store a Computer’s data. The data storage-retrieval process also needs be very quick, otherwise, it would be impossibly slow, working on a Computer!
The best, most popular
manufacturers of hard disk drives are Western Digital,
Seagate, Maxtor (now owned by Seagate, Fujitsu,
Samsung, and Hitachi. IBM used to make hard disk
drives but sold that part of its business to Hard Disks have come a long way since they were invented in the 1950s. The first Hard Disks were 20 Inches in Diameter and were called Winchester Drives, since they were a part of IBM’s then-popular Computers. They held a few Megabytes of data then.
Having said that, the fact is that Hard Disks have changed very little in the last 50 years or so. They continue to hold data (only, a few Gigabytes more…), comprise of magnetic platters on which data is written – much like a Gramophone record (only, their size has shrunk from the Winchester Drive’s 20 Inches to a mere 3 ½ inches now, with Notebook Hard Disks being just 2 ½ inches) and continue to be the main data storage component of the Computer. What has not changed is the drive mechanics or the way data is retrieved from the Hard Disk, what has changed is the way data is passed on to the Computer, for further processing. This is the Hard Disk Controller and we present the main types of Hard Disk Controllers in the question Hard Disk Technologies
You also have Solid State Drives that can hold Gigabytes of data. Such devices include External Hard Disks as well as their smaller cousins, the USB/ Micro/ Thumb/ Flash/ Pen Drives. We are not covering External Hard Disks or USB Dives in this section. Internal Hard Disk Drives continue to be based broadly on the same technology used by the Winchester Disk Drives. A Hard Disk is a very sensitive Computer part due to the following reasons:
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What does the interior of a Hard Disk consist of?
What kinds of damages/ errors does a Hard Disk show?Hard Disk errors may be one of the following types:
What are the precautions that need to be taken, so as to ensure that Hard Disks stay as healthy as possible?Keeping Hard Disks healthy will require you to take the following precautions/ steps:
A Hard Disk’s performance is measured by means of the following two parameters:
Apart from the above two parameters, Hard Disks are classified based on two more parameters, as follows:
The data rate or seek times of a Hard Disk do not depend exclusively on its RPM. It depends on the technology (IDE is slower than SATA, which is slower than SCSI as well as the circuitry making up the Hard Disk. However for the same Hard Disk technology, a higher RPM usually does mean smaller Seek Times and higher data rates. How is Data Stored on a Hard Disk?
So who writes the Sectors, Clusters and Tracks to a Hard Disk? You can, if you want to – the process is called Low-level Formatting of the Hard Disk. Low-level formatting of a Hard Disk marks off the beginning and end of each sector on it. The DOS utility FDISK is a Low-level Disk formatter, there are other utilities that do this as well.
During Low-level Formatting, you can also divide your Hard Disk into Partitions
– the process is called Partitioning. Partitioning a Hard Disk makes it look
like you have more than one Hard Disk. It is advisable to partition your Hard
Disk into a Primary, active partition of at least 30 to 40 Gigabytes size, to
hold the Operating System and all your Programs. The rest of your Hard Disk
should be used to hold your data files. This partition should also be at least
30 GB in size, so that it does not run out of space. If you have more space left
over, you may want to keep a third, empty partition. If you shoot a lot of
digital video and need to transfer your video files to your Hard Disk (to
convert into CDs/ DVDs), a large, empty partition will come in handy!
After
a Hard Disk is Low-level Formatted and Partitioned, it
next needs to be High-level Formatted as well. High-level Formatting writes
critical information like the file-storage structure, the File Allocation Table
(FAT), etc., thus readying the Hard Disk to hold files and folders. The benefit
of placing the Operating System and Programs in one partition is that if your
Hard Disk is damaged – say by a Virus, you only need to format that partition
and re-install your OS and Programs – your data will remain safe and intact, on
the other partition!
The Primary, Active Partition (the partition that contains your Operating
System) is usually given the Drive Letter C, with the remaining partitions being
named as Drives D, E, etc. The convention is that once all the partitions of
your Hard Disk are labeled by drive letters, the next-available alphabet is
given to your
The first physical sector of a Hard Disk is special. It contains what is called the Master Boot Record (MBR), which contains the following vital information:
In fact, the FAT is so important that Hard Disks permanently retain two copies of it, so that if one is accidentally erased or corrupted, the other can still seek and retrieve data from your Hard Disk!
Every Postal System needs a directory of addresses, a map of the city. A Hard
Disk too needs such a ‘map’ of its sectors, clusters, tracks and cylinders. It
is the area of the Master Boot Record (MBR) called the File Allocation Table
(FAT) that contains this information - the beginning sector and other
information about the location of each and every file on your Hard Disk.
You
can see how important the FAT is – if it is erased/
corrupted, the files cannot be reached, even though they are safe and actually
present on the Hard Disk! It is as if your address has been wiped out from the
face of your Express Courier letter: your house continues to be where it is
located, but Fed Ex does not have your address, so as to deliver it to your
home!
In
fact, the FAT is so important that Hard Disks permanently retain two copies of
it, so that if one is accidentally erased or corrupted, the other can still seek
and retrieve data from your Hard Disk!
Running ‘chkdsk /f’ under the DOS Prompt or ‘scandisk’ from within Windows allows the Computer to check the FAT against the actual location of each file on the Hard Disk, and correct errors if any. Note that the ‘chkdsk’ option without the ‘/f’ switch only checks for FAT errors, without correcting them.
The importance of defragmenting your Hard Disk is also evident from the structure of the FAT. Suppose you have a file that is 513 Bytes big. Assume that the first 512 Bytes are written to Sector X. If the last Byte of the file is written to the very next Sector, the Hard Disk platters or its Actuator arm need minimum movement alone, to fetch the file in its entirety. However, if it is written on a different platter – a different Cylinder and on a different Track, the Hard Disk needs some movement to fetch the file in its entirety. This not only increases the Seek Time and decreases the Data Rate, it also causes your Hard Disk to wear out faster! For, all moving parts have a finite life, thanks to friction!
Also, in case a sector is
incompletely filled, the remaining space cannot be used to hold a different file
– a new file will have to be begun on a new, blank sector. Thus in the example
of the file of 513 Bytes size, the first 512 Bytes will occupy a single sector,
while the remaining 1 Byte will occupy an entire sector, with the 511
Bytes remaining on it being un-utilizable for storing a second file! What are the types of File Systems in vogue? Although the Hard Disk has evolved very little over the years in terms of technology, its Capacity has gone up manifold. This has been made possible due to advances in the FAT structure – one cannot increase the number of platters too much, since the Hard Disk needs to be fitted into the Computer! Today's File System is definitely the NTFS system, though we will talk briefly about the earlier systems as well, in the interests of continuity of content.
Early Operating Systems up to Windows 95 OEM Release 2, i.e., DOS and Windows 95
Original release, had FATs that were 16 Bits in length. These were therefore
called FAT 16. FAT 16 limited Hard Disk size to 128 Megabytes, for a Cluster
size of 2,048 Bytes. Although up to 512 Megabytes is theoretically possible if
one assumed a cluster size of 8,192, the Cluster size would become unmanageably
large and inefficient. DOS 5.0 and later versions were able to provide for
support of hard disks up to 2 Gigabytes with their 16-bit FAT entry limit, only
by supporting separate FATs for up to four partitions.
With Windows 95 OEM Release 2, it became theoretically possible to support up to 2 Terabytes, as the FAT system of this release was 32 Bits in length. This implementation of the FAT is called FAT-32. In practice, Computer users were able to purchase 5 or 10 Gigabyte Hard Disks, with the FAT 32 system.
Today, Windows NT, XP 2003 and the latest Notable features of NTFS include:
In Brief, this is how the current NTFS
File System works:
When a hard disk is formatted (initialized) under NTFS, its physical space is divided into partitions or major divisions. Within each partition, the Operating System keeps track of all the files that are stored by that Operating System. Each file is actually stored on the hard disk in one or more Clusters of a predefined, uniform size. Under NTFS, Clusters sizes range from 512 Bytes to 64 Kilobytes. Windows NT provides a recommended default cluster size for any given drive size. For example, for a 4 Gigabyte drive, the default cluster size is 4 Kilobytes, and so on. Like Sectors under FAT, Clusters are indivisible under NTFS. Thus, a file that occupied 4,097 Bytes will be located on 2 Clusters – the first one containing the first 4,094 Bytes of the file, with a second Cluster containing only the last 1 Byte of the file – its remaining 4,095 remaining un-utilized for storing any more data!
Cluster size is a trade-off between efficient use of disk space and the number of disk accesses required to access a file. In general, using NTFS, the larger the hard disk the larger the default cluster size, since Computer users would always prefer increasing performance (i.e., fewer disk accesses), at the expense of some Hard Disk space inefficiency.
When a file is created using NTFS, a record about the file is created in a special file, the Master File Table (MFT). The MFT is used to locate a file's possibly scattered clusters. NTFS tries to find contiguous storage space that will hold the entire file (all of its clusters). Each file also contains, along with its data content, a description of its attributes, called its Metadata. For more information on Metadata, click here. What are the important Hard Disk technologies? We have discussed how the File Allocation Table (or Master File Table, MFT, under the NTFS system) allows for larger data storage on Hard Disks. The MFT system of NTFS also allows in-built data compression, security and higher data transfer rates, due to the fact that each NTFS Cluster stores information about the data it contains. However, it is the Hard Disk technology used - the circuitry of the hard Disk as it were, that really influences Data Transfer Rates. In modern Hard Disks, this ‘circuitry’ is built in to the Hard Disk’s PCB (Printed Circuit Board) itself.
The drive's internal logic board contains a microprocessor and internal memory, as well as other structures and circuits that control what happens inside the drive. It is in fact a small PC within the hard disk itself! The control circuitry of the drive performs the following major functions:
We briefly discuss the different Hard Disk technologies below: There are only three main standards used to interface internal hard disk drives, CD drives, etc. - the IDE ATA (Integrated Drive Electronics Advanced Technology Attachment), SCSI (pronounced ‘Scuzzy’, it stands for Small Computing Systems Interface) and SATA (Serial ATA) standards. The IDE ATA standard is also called PATA, which stands for Parallel ATA) and it has been available for many years now. IDE Drives were the earliest Disk Drive technologies used for Personal Computers. Even today, IDE Drives form the majority of Hard Disks installed on Computers, worldwide. It is very likely that if your Computer is a Pentium IV (or earlier model), your Computer uses the IDE technology. SATA, which is fast becoming the standard for Desktops and Notebooks, is available in two versions - SATA 150 (the first version) and SATA II 300. They are very similar to the IDE Controllers, yet, SATA is faster than PATA (IDE ATA). Thus, SATA exhibits higher Data Transfer Rates and lower Seek Times. SATA Drives are commonly available in RPMs of up to 10,000, (as against IDE’s 7,200 RPM) further boosting their performance.
The SCSI Hard Disk Controller is significantly different from IDE and SATA Controllers. They are also costlier and have been around for some time, though they have been used exclusively on Servers, high-performance Desktops and most often, on non-PC platforms such as UNIX machines. SATA drives can theoretically perform faster than SCSI. This lead to the emergence of a new SCSI standard (called SCSI SAS – for Serial Attached Storage), employing a Serial Controller, much like SATA itself A brief recap will help us understand Hard Disk Defragmentation a little better:
File Fragmentation (also called Disk Fragmentation)
results in the following problems:
Since it is the Operating System and the Hard Disk’s controller mechanism that reads/ writes data to the hard Disk, there is nothing you can do, to keep Hard Disk fragmentation under control. At least, merely by being careful about how you read/ write data to it! Are there automated solutions for tackling Hard Disk problems, including Defragmentation?The only solution to reducing Hard Disk fragmentation is the use of Defragmentation Software. Excellent Software for analyzing the extent of defragmentation of your Hard Disk is available. They let you check the Hard Disk FAT (or MFT, if it is an NTFS Hard Disk) for errors, present you easy-to-understand Defragmentation Reports, give you the right recommendation on what you should do for reducing fragmentation and the means to carry out the recommendation quickly and safely, without loss of data.
The best solutions under this category also let you do the following:
On the other hand, if you have uninstalled one or more programs merely by deleting their folders, you need to first clean up your Windows Registry entries, before defragmenting your Hard Disk. Here are your choices for cleaning up your Windows Registry - for the full review, click here.
Which is the Best Hard Disk Management solution?
Click here to read about the Disk Manager that has won our Thumbs Up!
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