Mirror Magazine

Mirror Magazine Techno Page By Harendra Alwis

Anatomy of the hard disk
The most important component (s) of the hard disk are its platters. They are round flat disks that are coated with a special material so as to enable them to store data in the form of patterns of magnetic particles. Then they are mounted on an axle (spindle) that is driven through the centre of the disks. When in use, these disks rotate at a very fast speed driven by a motor that is attached to the spindle.

Special read/write heads are mounted on ‘robotic arms’ which are capable of changing their position on the disk from its centre up to the rim, making the whole surface area of the disks available for read/write operations while the disk is spinning. There are two read/write heads for each platter – one on each side.

The positioning of the read/write heads is a critical operation in the hard disk and is carried out by the ‘Actuator’. The other activities of the hard disk and its communication with the rest of the computer system are handled by the ‘Logic Board’. Then, of course, there are the cables and small circuit boards within the hard disk, each assigned a unique function.

The entire hard disk must be manufactured to a high degree of precision due to the extreme miniaturization of the components and the importance of the hard disk’s role in the PC. The main part of the disk that contains the platters is isolated from outside air to ensure that no contaminants get onto the platters, as they could cause damage to the read/write heads and the platters themselves.

Data storage
The surface of each platter on the disk can hold billions and sometimes trillions of individual bits of data. These are organized into larger “portions” for convenience and to allow for easier and faster access to information. Each platter has its information recorded in concentric circles called tracks. Each track is further broken down into smaller pieces called sectors.

Each of these sectors hold 512 bytes of information. Think of these sectors as individual drawers of a very large filing cabinet, each with a unique serial number assigned to it. The computer uses these numbers to identify the location of the ‘drawer’ when it reads the data stored on them or when new data is written in.

Imagine how many individual drawers there would be if a modern 40GB hard disk is divided into sectors, each containing just 512 bytes! This would be a severe strain on the computer’s performance because it is not easy to keep track of so many individual sectors. Because of this, the individual sectors are again grouped into ‘clusters’ to make things easy. Instead of numbering each sector we can number the clusters. The number of each cluster will be its address within the disk. You can choose the number of ‘sectors’ you want to include in a ‘cluster’ at the time of partitioning a disk drive.

Data fragmentation
Let us assume that a cluster has the capacity to store about 4 kb and you want to save a file of 2 kb on the disk. The system cannot break down a cluster into smaller fragments, so your 2 kb file will occupy the whole 4 kb cluster and make it ‘unavailable’ for writing operations. In the same way, a 5 kb file will span two clusters, occupying one whole cluster of 4 kb and a 1 kb fraction of another, making both ‘unavailable’.

This is called data fragmentation. There is also another phenomenon which bears the same name. Usually files are stored in clusters that run sequentially together on the disk, but this is not always possible because while writing a file sequentially on the disk, clusters that already contain valid data could stand in the way. When that happens, the write-head will be compelled to ‘move to another place’, resulting in a single file being fragmented and written at different physical locations on the disk.

Then, when reading such a file off the disk, the read-head will have to travel across the surface of the disk several times to read the single file, thus causing a considerable delay by computer standards. You can rectify this by running a ‘Disk Defragmenter’ tool, which would rearrange the files on your hard disk so that each file will be stored sequentially and physically on neighbouring clusters on the disk, enabling the read operations to function efficiently.

A good defragmenter will also arrange your most frequently used files in the faster regions of the disk. Write in with your views; and bear with me if I am unable to reply each one individually, although all your comments are much appreciated.

Improve your computer literacy
Taxonomy - The science of categorization, or classification of things based on a predetermined system. In reference to web sites and portals, a site’s taxonomy is the way it organizes its data into categories and sub-categories, sometimes displayed in a site map.

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Unlike a malicious hacker, who may disrupt a system for financial gain or out of a desire to cause harm, the hacktivist performs the same kinds of disruptive actions (such as a DoS attack) in order to draw attention to a cause. For the hacktivist, it is the Internet way of resorting to civil disobedience and protest.

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