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Category: Computer Hardware

Inside-Out – Part 1: Hard Drives

Written by Leon on August 25, 2011 at 1:58 pm with No comment

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This article is all about hard drives, how they work, what they’re made of and what they do! Starting with the casing right through to the motor that makes it spin, this article hopes to give the reader an in detail insight into the world of hard drives and there importance.

Where did they come from?

IBM (international business machines) introduced the hard drive in the late 1956 with the IBM 350 storage unit being the first true hard drive. Soon after their introduction they became common place in mainframes and mini computers. However Hard drives where expensive and therefore did not become commonplace in standard PC’s until the late 1980’s, by which time only the cheapest computers did not come with hard drives as standard. Another factor was the size of the unit, unlike today where a hard drive typically comes in a 2.5” or 3.5” form factor, the IBM 350 weighed over a ton and took up as much space as a typical full size server rack of today!

By this point you may be asking if these hard drives where so big and heavy why did they take over so rapidly from the previous method of using tape? The reason for this is simple, access times. Unlike tape, hard drives can access data much more quickly and efficiently than a tape. A tape as to wind backwards and forwards to retrieve different items of data, whereas a hard drive has to simply move a read/write head over a rotating magnetic disc and collect the data. This revolution in computer storage allowed computers to process data much quicker and make the information much more readily available.

Finally unlike other technologies that have come, gone, been replaced by quicker faster options, such as the now what seems prehistoric floppy disc. Hard drives have had some amazing staying power. The reason for this was their ability to evolve with technological advances and remain in demand. As the need for quicker, larger storage increased so did the capacity and speed of the hard drives. Additionally as there capacity increased there sized decreased to the size we know today, and even smaller if required. Another important factor is that until recently with the introduction of ‘solid state drives’ the mechanical hard drive has had very little (if any) competition as a secondary storage unit. All of these factors contribute to the reason the hard drive has been a true revolution to the computing industry right the way from 1956.

The Case

Many hard drives look the similar, regardless of the manufacturer; all tend to be rectangular with a black base and a shinier top. However boring the case may appear it provides some essential functions that allow the hard drive to function correctly. Starting with the obvious the case provides some physical protection to the internal parts, not only for little bumps and knocks but also from dust and other contaminants causing havoc on the read/write head and the magnetic disc. The lower half of the case is often cast aluminium, mainly because it’s light, conducts heat well and is relatively easy to cast due to its low melting point. The lower half of the case around where the motor sits is usually not flat, but is cast into bumps providing more metal for the heat to dissipate through. This is an important addition to the case as hard drives can get very hot when in use and as the temperature passes the 40 degrees Celsius mark performance can decrease dramatically, even to the point of failure.

The upper part of the case, or the lid, is usually much thinner, again made from aluminium. If you look closely around the top and/or sides you can usually find a small hole/s with the instructions wrote nearby “do not cover” (or words to that effect). This small hole is known as a “breather hole” and provides another important function to the internal parts. The breather hole lets air in and out of the inside of the drive; this allows the pressure to remain constant and stable, whilst also preventing the build-up of moisture. At this point you may be thinking “if dust and dirt is so dangerous to the internals of a hard drive, surely a hole in the top is a bad idea?” This is a fair point! However behind the holes are very dense filters and often a compound to capture moisture, this prevents any dirt, contaminants or moisture entering the drive, whilst still allowing air in and out.

The PCB

The PCB (Printed circuit board) or logic board as it is in this case is the small circuit board you can see on the underside of the drive. This is the board that makes everything ‘tick’ from the disc spinning round to the read write head whizzing across its surface. Typically the logic board has a controller chip, a ROM chip, a RAM chip and a voice coil controller. All of these chips work in harmony to make sure all of the components work correctly. Starting with the controller chip, this you might say is the ‘boss’ handling the communication between the hard drive and other components in the system whilst managing the other components on the logic board. Secondly the ROM (read only memory) chip provides all of the drives base information, such as capacity. Thirdly the RAM (random access memory) chip provides the hard drive with a buffer allowing a cue of instructions to be saved temporarily while other instructions are being processed. Finally the Voice Coil Controller chip manages all of the read and right operations that take place between the read/write head and the magnetic disc.

//Inside the box

After reading all of the operations that happen outside of the case you may expect that inside the case would be bursting with electronics and advanced circuitry. However that’s not the case, the inside of a hard drive is relatively simple and is made of the following key components:

The Spindle motor

The spindle motor provides the rotation to the platters, allowing them to spin at extremely high speeds (typically 7500RPM – 10000RPM in home computers currently). The problem with motors is they tend to vibrate whilst in use, especially when rotating at high speeds. This is bad news for a hard disc as the tracks on the platter are so close together that if the platter was to vibrate the read/write head would write data over multiple tracks, along with numerous other problems such as the head scraping across the surface. Therefore the motors in hard discs are extremely high quality, brushless motors that use liquid as appose to ball bearings to lubricate the spinning parts. This method allows the motor to be more durable, quieter and practically vibration free.

Super strong magnets

A special type of magnets are used in hard drives that provide a super strong grip with very little magnetic field, these magnets are called ‘neodymium’ magnets. These magnets are ideal for the job because only inches away lies a highly sensitive magnetic disc that can be corrupted by magnetic fields. However because these magnets have such a small field they do not interfere with the sensitive magnetic platter. Additionally that provide enough force to move the armature rapidly across the surface of the platter allowing is to read and write data.

The Armature

The Armature houses the read/write heads of the end of its arm and swoops across the hard disc has it rotates reading and writing data to the relevant tracks. The armature typically starts at the outer most part of the platter and works inwards as the platter is populated with data. Because the disc is rotating beneath the platter the armature only has to move from the centre to the edge to read and write data.

Read and write heads

The read and write heads are responsible for the writing and reading of data to the platters of the hard drive. The read and write heads are better viewed under a strong magnifying glass or microscope as they are so small. Contrary to popular belief, although they appear to make contact with the platter they actually float over its surface, making no contact at all. However the distance between the head and the platter is around half the thickness of the average human hair, so it is understandable how this misconception arose. The most fascinating parts of the heads is that they actually ‘float’ of a cushion of air that is produced from the high speed rotation of the platter below, thus proving while air pressure is so important.

The read head is made up of alloy layers whilst the write head is composed of a small coil. The armature splits at the end allowing read/write heads to exist on the top and bottom of every platter that is installed in the hard disk.

The voice coil

The voice coil in a hard drive moves the armature left and right at high speed whilst still remaining precise. Additionally it provides the armature with stability to prevent it wavering of course. The armature is basically tightly bound laminated copper cable that sits on top of the neodymium magnet mentioned earlier, as the current changes this makes the coil move to different positions and therefore moves the armature.

This is where it ends!

Hard drives have been a miracle in the advancement of technology and data storage and will most likely remain as such for years to come. Although the mechanical hard drives days may be numbered as the solid state drive slowly creeps in, they are still providing us with an irreplaceable resource and will continue to do so in the future.

This article is part of the Inside-Out series of articles provided by East Midlands IT, if you use any information in this article please reference it by using this link: http://www.eastmidlandsit.co.uk/inside-out-part-1-hard-drives/