Performances of a hard disk
We have been talking about the hard disk in detail during the last few weeks, which included descriptions of the various components and how data are stored in the hard disk. The topics we covered will be sufficient to give you a good idea of how the hard disk actually works. But all that information will be of little use if you do not know the practical performance issues of the hard disk. You will need to know whether a given hard disk is ‘good’ or ‘bad’. So this week let us talk about what you need to know before you buy a hard disk.

The performance of the hard disk is one of the most underrated aspects of overall system performance. B ut it is important because hard disks are one of the slowest internal PC components and, therefore, often limit the performance of the system as a whole because even as one of my teachers used to say, “A chain is only as strong as its weakest link”. Quality and reliability are critical with hard disks because they are where your data reside! No other PC component can lead so readily to disaster if it fails. So when considering the daily use of hard disks, and contemplating a hard disk purchase, PC users often ask three key questions:

Is this hard disk fast? Is this hard disk well manufactured? Is this hard disk going to last? You already know that a hard disk has only a few basic functions which involve writing data received from the system on to the disk and providing the system with data already available on the disk. When considering performance, it is this ability to move data into or out of the hard disk that we need to measure. There are two separate parts of this data movement job. For a write, the data must be fetched from the system and then written to the correct sectors on the disk. For a read, the process is reversed; data must be read from the disk and then transmitted over the hard disk interface to the system.

There are many factors that contribute to the overall performance of the hard disk and it is difficult to go into all the details here. Suffice to say that they involve measurements of how fast the platters spin, the speed of the spindle (typical speeds of drives today range from 4,200 RPM to 15,000 RPM), internal and external transfer rates and so on. One thing you need to know is that even the way in which you format the disk (the cluster size you specify) contributes to the performance of the hard disk. If summarized, the larger the cluster size, the faster the hard disk will function but at the cost of higher memory wastage and vice-versa.

Noise and vibration reduction, cooling, seek time, settle time, command overhead time, latency and access time are also features you should look into. When it comes to ‘time’ and latency you would intuitively know that the lesser time it takes – the better. Some of these depend on the type and workings of the hard disk – system interface. For example, a type of hard-disk interface that puts less of a burden on the CPU will account for greater system performance.

As mentioned, there is much more to the inner workings of the hard drive than we could ever hope to include in a weekly discussion such as this. If you need to know any specific details about hard disk drives, don’t hesitate to write to Techno Page, but for the moment we will break off to a similar field – that of CD ROM/RW and DVDs.

Molecular logic gates and chemical computers
In today’s world, comput ers play a major role in all imaginable spheres of life. Integrated circuit (IC) technology has reduced their sizes to notebooks and palm tops from the mammoth room-size monsters of 50 years ago.

But as we decrease the size of a computer (i.e. its internal electronic components) to the atomic level, the laws of Newtonian physics that govern the ordinary PC or laptop that we use, gradually become irrelevant and inapplicable. At the nanometer level, the laws of quantum physics will govern the operations of internal components of such minute and powerful computers.

Computers of this nature are known as quantum computers. Currently, much research is being carried out in the fields of nano machines and quantum science to develop a machine that will out-perform and out-smart the ordinary computers that we use.

Recently, a new kid has entered the block in the computer scene. Two researchers at Queen’s University, Belfast have demonstrated that a computer, which is totally different to a quantum computer or for that matter any normal computer, can be successfully constructed. They have developed molecular logic gates that can be considered as the fundamental building blocks for the development of a “Chemical Computer”. True, all computers are made of some form of chemical substances, but this is different from anything we have seen so far.

Chemistry professor A. Prasanna de Silva and post-doc Nathan D. McClenaghan have developed various types of molecular logic gates, simply by using different wavelengths of light to look at the ion-indicator action of certain dyes. They have simultaneously shone two beams of light with different wavelengths on the indicator solution and obtained two types of logic gates - for example ‘YES’ and ‘NOT’ gates (there are also ‘NO’ gates which are different from ‘NOT’ gates) –simultaneously. This is the first time that a common ion indicator has shown logic gate activity and more importantly multiple logic behaviour.

‘YES’ logic is obtained when a high input (1) gives a high output (1) and a low input (0) gives a low output (0), whereas ‘NOT’ logic occurs when inputs of 1 or 0 result in outputs of 0 or 1 respectively.

The other two molecular logic gates developed by de Silva and McClenaghan are the PASS 0, which gives an output of 0 irrespective of what the input is and PASS 1, which gives an output of 1 in the same way - when the input could be either 0 or 1. This new molecular logic system uses ions (Ca2+) as inputs. The outputs are the light transmittance values of the indicators at specific wavelengths. These calcium-dependent spectra of the systems are reminiscent of the pH dependent spectra of common pH indicators such as methyl orange.

The multiple logic behaviour is the most important attribute found by de Silva and co-workers in their research. Professor de Silva compares the multiple logic behaviour of ion indicators with that of quantum computers.

Quantum computers are thought to operate simultaneously on all possible combinations of a quantum bit (qubit) string. These simple ion indicators show superposition of logic gates, whereas quantum computation involves superposition of input qubit strings. Lately, the researchers have shown that two distinct chemical systems can be operated in parallel to carry out simple arithmetic operations.

Prof. de Silva notes that since his molecular logic systems are solution based, they do not employ connecting wires and are, therefore, unlikely to integrate with traditional solid-state systems. Nevertheless, it may be possible in the future to design ‘wet ’ computers that work more like the brain, relying on membrane bound molecular processors similar in nature to the human brain. Wet molecular logic systems may be used for information gathering as well as for information processing like in medical applications, for example, as miniaturized diagnostic systems.
Sent by Nuwan Karunaratne

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