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computer hard disk

Components of a hard drive

A hard drive consists of hard disk assembly and front read/write control circuit. Hard disk drive assembly belongs to mechanical device and every component of the assembly is composed of high precision machinery parts. The front read-write control circuit is made up of a group of complex circuits and is responsible for the modulation of exchanging the signal types between hard drive and CPU and also amplifies them.

1. Hard Disk Assembly

Hard Disk Assembly is the hardcore of a hard drive, which includes platters, spindle motor, read/write magnetic heads, actuator motor and so on.

Now let’s have a close look of each part:

Platters: the platters of a hard drive consist of one or more overlapped flat circular disks, which holds the recorded data. The surface of these overlapped metallic disks is extremely flat and smooth and is covered with a thin layer of magnetic material. These disks are separated by washers.

From physical point of view, platter is divided into Magnetic surface, Track, Cylinder and Sector.

Magnetic surface: Magnetic surface refers to the upper or lower side of a disk. The upper side of the first disk is side 0, the lower side of the first disk is side 1, the upper side of the second disk is side 2…

Read/write magnetic head: As every side has a corresponding read/write head, we can call these magnetic heads head 0, head 1, head 2…

Track: tracks are the thin concentric circular on a disk divided when formatting the disk. The outermost track is called track 0 and towards the center of magnetic surface are track 1, track 2… and the most central part is called Landing Zone, and data won’t be recorded there. Landing Zone is the position where the magnetic head starts and stops.

Cylinder: Tracks with the same radius of all the disks can form a barrel-like figure called Cylinder. Cylinder can be used to calculate the logical disk capacity.

Sector: Sector is the basic unit for disc storing data, which is the area between the two adjacent radiuses after dividing each track into equal segments. Then, it is not difficult to understand why every track has the same number sectors. The beginning of a sector contains the unique ID of a sector. The sectors are separate by gaps, which can be conveniently recognized by the operating system. Sectors are numbered from 1.

Spindle motor: spindle motor is specially used to drive the disk to spin with high speed. The rotation rate of the recent popular hard drive is between 5400 revolutions hd3.gif

per minute/rpm and 7200 rpm. 10000 rpm belongs to high speed hard drive. The rotation rate of hard drives used by network server and some graphic processing devices is generally varying from 15000rpm to 2000rpm. Some are even higher.

Read/write magnetic head: read/write magnetic head is responsible for transforming the platters’ magnetic field into electrical current when read and write data.

Actuator motor: actuator motor is used to drive the magnetic head to actuate. Actuator motor and magnetic head are connected by actuator arm.

2. Front Read/Write Control Circuit

Front read/write control circuit is also called pre-amplifier circuit. It has two main functions:

First, it is used to convert binary code to analog signals. When the data needs to be written, it is the binary code representing the data that is transferred from the center processing system to the magnetic head. This circuit must be passed by those binary codes. Then it is able to convert those binary codes to analog signals that can change the current size and transfer the analog signals to the magnetic head.

Second: it is responsible for converting binary code to analog signals and amplifies the signals. When reading data, what the magnetic heads obtain is the current generated from the magnetic field. When the current is transferred to the center processing system, it also must pass through the preamplifier circuit. At this moment, this circuit will convert the current which represents the analog signal to the central processing system recognizable binary code, and amplify the weak signal.

Now let’s learn something about the hard drive types:

Basically, there are four types of hard drive types: IDE hard drive, fibre channel hard drive, SATA hard drive and SCSI hard drive.

1. IDE hard drive
IDE is short for Integrated Drive Electronics. It originally refers to hard disk drive that combines the hard drive controller and platters together. This method will reduce the cable number and length of a hard drive interface and also the reliability of data transmission is enhanced. Besides, it becomes easier to produce hard drives. As to users, the hard drive installation is more convenient. IDE hard drive has been developing since it is born. Its cheap price and strong compatibility make it irreplaceable by other types of hard drives.

2. Fibre channel hard drive
Fibre Channel is primarily designed for network system. However, with the storage system’s increasing need for speed, it is slowly used in hard drive system. A fibre channel hard disk is developed to improve the speed and flexibility of the hard drive storage system. Its appearance improves the communication speed of multiple hard drives. The main features of fibre channel are hot-swap, high speed bandwidth, remote connection and greater number of connected devices. Fibre channel is designed for multiple hard drives environment like servers and it can satisfy the requirements for high data transmission rate.

3: SATA hard disk
SATA hard disk using the SATA interface and another name of it is Serial interface hard disk. It is the main development direction of future PC. Serial ATA uses a serial connection mode, and Serial ATA transmits the data in serial mode and it only transmits 1 bit of data at one time, which can reduce the number of pins of SATA interface and also make the connecting cable number fewer. As a result, the efficiency will be higher. It also has the stronger error correction capability. Once the error is found, it will correct it automatically, so this greatly improves the security of the data transmission. The new SATA uses a differential-signal- amplified- system, and this system can effectively filter the noise from the normal signal. In addition, Serial interface has the advantages of simple structure and supporting hot-plugging.

4: SCSI hard disk
SCSI hard disk refers to Small Computer System Interface. This interface type is totally different from IDE interface. The IDE interface is the standard interface of PC, but SCSI is not, it uses the 50 pin interface and the appearance of the interface is similar to the general hard disk. As SCSI hard disk has good performance, high stability, a wide range of applications, multitasking, large bandwidth, low CPU occupancy rate, hot-plugging and other advantages, it is widely used on the server. But its high price makes it difficult to become popular like IDE hard, so SCSI hard disk is mainly used in high-grade, high-end servers and workstations.

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