Computer hard drive

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Engineering materials (Disk drive)

Introduction

Computer hard drive refers a device that is used for storing computer's information including all the programs installed and the operating system. It is a very essential device in a computer and hence the manufacture of a hard drive must be done carefully and professionally so as to ensure that it perform effectively and efficiently. This can only be achieved if proper choice of the engineering materials used to make the components of a hard drive is made. Making the hard drive with right engineering materials improves its reliability and durability hence ensuring that information stored in it is not lost easily (Television Society 1996). It is possible to lose all the data stored in a hard drive forever if something goes wrong in the hard drive. To prevent this modern hard drives are made with a lot of cautiousness and using a very high technology thus making them to be more reliable than the previous ones (Parsons & Oja 2008). This paper discusses the various components of a computer hard drive and the factors considered in selecting the materials for making each of the component.

Major parts of a computer hard drive
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A computer hard drive is made of two types of components namely: internal and external components. External components refer to all those components located in the printed circuit board commonly known as the logic board. Internal components on the other hand refer to all those components that are located in a chamber that is sealed commonly known as hard disk assembly (Bigelow 1996). It is important to note that any attempt to open a hard drive renders it unusable because assembling of hard drive components is done in very clean rooms and then sealed. This is because hard drive is made of some components which are very sensitive and can be destroyed by just a minute dust particle as it spins at very high speed. A dust particle can not only lead to permanent data loss but also the disc surface is physically destroyed. This means that internal components of a hard drive can only be replaced by companies with clean rooms and not just regular technicians. The components of a hard drive include:

Platter

This is a circular, flat and hard metal disk mounted inside a disk drive. There are several platters which are mounted on fixed spindle motor which helps in creating more data storage surface in a smaller area. Platters are usually made of aluminium or glass substrate which is covered with a thin layer of cobalt alloy or ferric oxide. A thin coating is then deposited using a special manufacturing technique on both sides of the substrate material. The thin coating where data is stored is known as the media layer. A thin lubricating layer is used for protecting the magnetic media which is applied to the surface of the substrate material. It is argued that (Mee, Daniel & Eric 1996) the purpose of the substrate material is solely to provide support to the media layer. The media layer is formed of a thin coating of magnetic material applied to the surface of platters and this is where the actual data is stored. The media layer has a very small thickness, to obtain this thickness a method known as magnetron sputtering is used to deposit the coating on both sides of the substrate. To protect the magnetic media a super thin lubricating layer is applied on it. This layer helps in protecting he disk from damage which may be caused by foreign material entering the drive or accidental contact from the heads (Muller 2003). Modern hard drives are usually made with a zone known as a landing zone where no data are stored. This is the area commonly known as Contact Start/Stop (CSS) zone is used for parking the heads in case of unexpected power loss. Initially, hard disks did not have a landing zone in the platter hence the heads would land on the data and thus incase of unexpected power loss data would be lost. Platter has got three divisions namely: tracks, sectors and clusters. It is also possible for a hard drive to have several platter discs as shown in figure 2 below.

Drive heads (Head Stack Assembly)
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Drive heads refer to very sensitive precision instruments inside a hard drive. Pogue (2002) argues that drive head are one of the most important parts of a hard drive and are generally the most frequent cause of hard drive failure. They are responsible for making it possible the actual data reading and writing in a hard drive. They write magnetic information onto the platter making minuscule and extremely fast movements to specific points on the platter. The heads are held in place by actuator arm just about a micron away from the platter surface. According to Jacob, Spencer & Wang (2007) the number of heads in a hard drive is determined by the kind of the platter in the hard drive because each platter require one head for each surface of the hard drive which have to be read simultaneously by the head i.e. if the platter in the hard drive is two sided, they will definitely require two heads to read the sides of the platter. The heads in a hard drive are stuck together in arm which makes all the heads to move together. To ensure that drive heads do not land on data zone in case of power interruption or due to other malfunction, modern hard drives have a means of parking the head either in a landing zone or automatically unloading the heads. This is done by use of a spring or by use of inertia in the platters. During this time, the spindle motor acts temporarily as a generator providing power to the actuator. The tension in the spring is used for pushing the heads toward the platter (American Society for Nondestructive Testing 1998). When the platter is spinning the heads are usually supported by air bearing and thus they do not experience any physical contact or wear. The figures below show the drive head and how they are positioned.

Actuator arms are used for moving the disk heads to the proper area of the platter. The drive heads are mounted on actuator arm which moves them in order to accurately read and write the information. The actuator arm is also used for keeping the drive heads at an optimal distance from the platter so as to protect the disk and also preserve its speed and efficiency. Muller (2003) argues that the actuator mechanism is used for moving the actuator arm into the right place to read and write data to the platter. This movement is done by use of a motor or a magnetic coil. Positioning of the actuator arm is shown on the figure below.

Spindle

This is used for spinning the platter at a certain measured speed so as to allow the drive head and actuator arm to be able to utilize the entire surface of the disk. Data transfer speed is a very essential feature in any computer, to achieve this; the hard drive platter must be spun extremely fast by the spindle. Minasi (2005, p. 56) explain that modern drives today can reach an average speed of 4800 to 7200 rotations per minute. The faster the rotation the faster the drive is and hence less time for reading and writing data. Modern drives have increased speed due to the adoption of solid state drives with very few moving parts.

Ribbon Cable

This is used for attaching the drive heads to the controller board (Bhambri & Kamar 2008)

Logic Board (Circuit board)

All the circuitry in charge of controlling the hard drive is located on the logic board. The logic board is located on the back side of the hard drive and is usually green in color. This is where all the electronic capacitors, resistors and other pieces of a hard drive are held. The circuit board contains basic electronic instruction commonly known as firmware which is used for telling the board how it should execute its functions. This is where the data transfer cable (PATA, SATA, IDE or Ultra IDE) and power cables are located. Floyd (2002, p. 139) indicate that circuit board gives instructions to the other components of the drive after receiving electronic impulses which ensure that they all work in tandem to produce the desired results. According to Askeland & Phule (2006) the circuit board is usually configured according to the type of the disk drive but their operation is basically the same . The figure below shows an example of one type of a logic board.

Factors considered in selecting the right material for making hard drive components
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Having reviewed the various components of a hard drive, it is important that we understand the engineering consideration given in selection of materials for making those component (Soper 2004). We begin by discussing the factors considered in selecting the choice of material used in making platter. Hard drive platter is usually made of aluminium alloy substrate coated by a magnetic material (iron oxide) used for data storage. The main purpose of the substrate is to provide support which means that the material to be to be used for its manufacture must be rigid. According to Kaplan (2004) aluminium alloy is preferred because it can offer the rigidity required and also it is light in weight, magnetically inert, stable readily available, not expensive and easy to work with. Heinrich & Bland (2005, p. 98) argues that the selection of a light material is important because you do not want to make a hard drive which will be very heavy to lift also the material should be readily available and cheap so as to ensure that it is possible to always have access to material for making the hard drives due to the increased demand for computer in the modern world and at a cost which is affordable. According to Brian (2002, p. 212) technological advance demands the need to reduce the gap between the platter and the head and thus the material for making the platter should be very smooth and flat. For this reason there is a lot of demand for alternative materials for making platter. One of the most appropriate alternatives is the use of glass platter instead of aluminium platters because they can provide improved rigidity, thinner platters, better surface quality and they have a very good thermal stability (Aries Technology Inc 2007). Another advantage of glass platter is that they increase the efficiency and storage capacity of a hard drive which are very important in the modern computers. Also another change that is there in modern disk drive is that instead of iron oxide being used as the magnetic material, cobalt based alloy is being used because it is far much advanced.

The head stack assembly is the other component of a hard drive which requires utmost care when selecting the material to manufacture it. The assembly is made of a ferrite core and forms a structure commonly known as an E- block (Lacheisserie, Gignoux & Schlenker 2005). Ferrite material is used due to its properties (hard, brittle, durable and good magnetic properties). The E- block is then over molded with a plastic coil around it to increase it's mass to enable it have a high inertial hence increasing high access time. However, if the head drives are made of materials with a very high mass it would result to vibrations of the head stack assembly which may degrade the performance of the disk drive. To ensure that modern head drives do not have excessive mass their E block are manufactured using In order to avoid this, most of the modern disk drives have E blocks with a hybrid structure including a plastic over mold structure encapsulating a stamped individual arm made of metal. In most cases a thermoplastic material is used for example PPS blended with a glass filler material (Kumar 2002).

According to Zacker (2001) the hard drive spindle acts as a work horse for the hard disk and thus it has to be made of a material which is consistent, reliable and stable to withstand the thousands of hours of continuous use. The material should also be wear resistant and tough enough so that it can be able to execute its function without failure. Other factors considered in making in other components of the hard disk are reliability, durability easy to work on and above all they must conform to the set standards.

In conclusion, we have been able to learn the various component parts of a hard drive and their function. These components includes the platter, spindle, actuator arms, logic board, ribbon cable among other components all of them dedicated in ensuring that the hard drive performs it work efficiently. Since the hard drives serves a very major role of keeping data, materials used for manufacturing the components should be carefully selected putting into consideration the work of each individual component and the conditions under which they are subjected to. This is extremely important so as to ensure the reliabilities of these components hence preventing frequent hard drive failure and subsequent data loss.