internal parts of the hard disk

On a Hard disk, data is stored in the magnetic coating of the disk’s platters. The platter is a flat disk of either alloy or glass, with a spindle at the centre. Modern platters generally have a diameter of 3.5” in desktops or 2.5” in laptops, although smaller 1.8” drives are available for devices that require a micro-drive.
The spindle is rotated by an electric motor, and this causes the platter to spin. The speed at which the platter spins is measured in RPM (Rotation Per Minute) and a higher speed is usually reflective of a higher performance disk in terms of data writing and reading. Usual RPM is 5200 and 7200. Hard drives with 10,000, 15,000 RPM normally use SCSI (Small Computer System Interface). SCSI interfaces provide for faster data transmission rates (up to 80 megabytes per second) compared to standard Serial ATA (SATA) and hard drives and you can attach as many devices as you like to a single SCSI port. (SEE FIGURE 1)
The magnetic media holds the binary data as with tapes and floppy disks. The data is read from the surface of the platter by a set of ‘heads’ which are fixed so that they can only move between the centre of the platter and the outside edge. The heads are held just above the magnetic media by actuator arms that facilitate this movement across the disk’s platter surface. The heads are not designed to touch the platter surface as physical contact can cause damage to the magnetic media. Each platter has a top side and an underside, and there is usually a head for both. Therefore, a hard disk with 5 platters would have 10 heads.

When the disk is not in use, the heads are ‘parked’, which means they spring back to the outside edge of the platter until they called into action by another data read or write.
Data in the magnetic media is organized into cylinders - concentric tracks on the media that are further divided into sectors. A sector is the smallest allocatable logical unit on a drive and usually, but not always, is 512 bytes in size. When an Operating System such as Windows sends data to the hard drive to be recorded, the drive first processes the data using a complex mathematical formula that adds extra bits to the data. When the data is retrieved, the extra bits allow the drive to detect and correct random errors caused by variations in the drive's magnetic fields.
Next, the drive moves the heads over the appropriate track on a platter. The time it takes to move the heads is called the seek time. Once over the correct track, the drive waits while the platters rotate the desired sector under the head. The amount of time that takes is called the drive's latency which is measured in milliseconds. The shorter the seek time and latency, the faster the drive can do its work. Average seek time in the majority of hard disk drives is 10ms.
When the drive electronics determine that a head is over the correct sector to write the data, it sends electrical pulses to that head. The pulses produce a magnetic field that alters the magnetic surface of the platter. The magnetic variations recorded on the surface of the platter, is called “data”. Compare these magnetic variations with the grooves on a vinyl record that is read by the record player needle arm which reproduces the music recorded on it by scratching the grooves on the surface of a spinning record.
Reading data complements the recording process. The drive positions the read portion of the head over the correct track, and then waits for the correct sector to orbit around. When the particular magnetic variations that represent your data in the right, the drive's electronics detect the small magnetic changes and convert them back into bits. Once the drive checks the bits for errors and fixes any it sees, it sends the data back to the operating system.
What is a board swap?
Inside any Hard Disk Drive, (HDD), there is a Printed Circuit Board, (PCB) that contains the electronics that manages the HDDs activities.
Like any other PCB, it contains chips and other components that the manufacturer has designed to allow the HDD to function effectively. Each HDD manufacturer has its own proprietary firmware. Firmware is the chips that contain program instructions and is highly specific to each manufacturer and HDD. Firmware is continually updated and as a result, a given HDD may go through many firmware revisions as the manufacturer attempts to get better and better performance from the HD models that it sells.
It is not unusual for an HDD o go through dozens of firmware revisions during the model’s lifecycle.

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If a PCB becomes damaged, or a component burns out, it is possible to either mend or replace this PCB. Repairing the PCB is easier than replacing the PCB as a replacement would need to be found with identical firmware. With an HDD that is over 6 months old, the procurement of an identical revision can be time consuming and difficult.
What is a Head Crash?
A ‘head crash’ occurs when the heads of a hard disk drive touch the rotating platter surface. The head normally rides on a thin film of moving air entrapped at the surface of the platter.
A shock to a working hard disk, or even a tiny particle of dirt or other debris can cause the head to bounce against the disk, destroying the thin magnetic coating on the disk. AND THIS MEANS LOSS OF DATA!
Since most new drives spin at rates between 7,200 and 15,000 rpm, the damage caused to the magnetic coating can be extensive. At 7,200 rpm the edge of the platter is travelling at over 74 miles per hour (120 km/h), and as the crashed head drags over the platter surface they generally overheat due to friction, making the drive or at least parts of it unusable until the heads cool. Following a head crash, particles of material scraped free of the drive surface greatly increase the chances of further head crashes or damage to the platters.
Data stored in the media that is scraped off the platter is of course unrecoverable, and because of the way that data is stored, randomly over a disk surface, this data may be whole files or parts of many files.
The most severe head crashes are the ones where the entire stack of heads, crash on each of the platters in the stack. A violent movement, or shock, to a working hard disk drive usually causes this. The chance of a good recovery in these circumstances is often remote and is generally limited to partial files.
Levels of Complexity in Data Recovery
Logical corruption:
This means that the computer is unable to make sense of the data that is randomly stored across the disk. The HDD loses its logical format and does not show up in the system. Disk utilities can see the drive but it shows it as unallocated space. This is usually caused by the computer’s index system being damaged or corrupted. The data is still there, but the computer is unable to recognise it for what it is, and thereby unable to reconstitute it into a readable document or file. Where structural corruption is the cause of the data loss, your chances of getting all the data back are extremely good. With the use of advanced tools and professional software and disk editing methods, Data Recovery Doctors can return the hard drive to a state that is understood by the computer. The files are most often undamaged after recovery.
Electronics failure:
This means that the external electrical circuitry of the hard drive has failed. Recovery from a hard disk in these cases is possible, as long as a replacement circuit board can be located or the circuitry can be repaired by Data Recovery technicians. This is not as simple as it sounds, as each hard disk may go through many revisions during its life-cycle, and a revision specific for printed circuit board or PCB must located in our parts inventory, or must be ordered from our suppliers.
Mechanical failure:
This means that the internal mechanics of the hard disk drive have failed through internal factors such as age, or minor manufacturing defects, or as a result of external factors such as shock, heat or water. This is more serious than an electronics failure as the internal mechanics within a modern hard disk are very delicate, and have extremely small tolerances. Again specific revision parts are required, and the internal mechanics will need to be mended or replaced in order for the hard drive to be able to read the data again. The hard disk needs to be disassembled in a class 100 clean environment to prevent damage to the disk platters upon which the magnetic media stores the data.
Media damage:
This means that the magnetic media on the surface of the hard disk platters, has become damaged or corrupted. This is mainly caused by what is known as a ‘head-crash’, where the electronic heads that read the data, from the disk surface, actually crash into the spinning platter surface and begin to scrape the media away. Once magnetic media that contains your data is scraped away, and turned into dust, data recovery becomes extremely difficult and expensive. As a computer stores data randomly across a set of platters in a hard disk drive, a relatively minor head crash can damage many files. Whole files and sometimes parts of files can be recovered but it is likely that the quality of the recovery is going to be lower than another type of hardware failure. On many occasions, the media damage is so severe that little valuable data can be retrieved.
Undelete Files:
When a user deletes a file, whether accidentally or intentionally, the actual data is not destroyed, but the computer system now regards that data as no longer required.
The data stored on a hard disk drive, are pieces of the document in random areas of the magnetic media on the hard disk surface. It does this to speed up the time taken to ‘write’ the data. Where ever the ‘heads’ happen to be when the save command is received, they ‘write’ data to the magnetic media.
As bits and pieces of the file are stored in different areas, the computer system requires an index or map to be able to put the bits back together again, in the right order, to reconstitute the file. The index is stored in a FAT or ‘File Allocation Table’.
When one deletes a file, the entry in the table is removed, telling the computer that those areas that previously contained a part of a file, are no longer required, and are available for new data to be stored. The computer does NOT go and ‘over-write’ the original data, so it remains in place until another set of data is randomly stored there. As long as the ‘deleted data’ has not been overwritten by new data, it can be found, reconstituted and recovered. Once deleted, data is over-written by new data, it is virtually impossible to recover it.
If you re-install Windows and realize that your data is missing, stop installing any applications as the more data your write on the disk, the less the chances of data recovery will become.

A method of data storage that has become increasingly popular is the use of external hard drives. Home computer users today have more data than ever, and many find that the storage capacity of their computer's hard drive is not sufficient. As the usage of external hard drives increases, there is also a rise in the number of external hard drive failures. Listed below are various physical problems that cause external hard drive failure:
Accidentally Dropped the External Hard Drive
There have been many cases where the external drive has been accidentally dropped by the user. Many of these hard drives are designed to sit upright on a flat surface. This can cause the drive to be susceptible to tipping over. The easiest way to prevent this from happening is to allow the external hard drive to lay flat instead of upright. This can prevent tipping. Otherwise, you should place the drive in a safe location away from the edges of a surface.
Twisted Electrical Cords and Cables
Many times, twisted cords and cables can cause an external hard drive to be pulled off a surface onto the floor. It is always important to make sure cords and cables are not twisted and are a sufficient length to reach from the computer to an electrical outlet.
Using the Wrong Power Cord
If you have several different power cords in the vicinity of your external hard drive, it is important to make sure you are using the correct power cord with your hard drive. There have been many instances where a user has plugged a different power cord into their external hard drive causing a power surge which will overheat the hard drive.
Power Surges from Lightning Strikes
It is important to always power down and unplug your external hard drive during a lightning storm. A power surge from lightning strikes can cause external hard drive failure by overheating the hard drive.
Contact a Data Recovery Company If You Have Experienced External Hard Drive Failure
If the data on the hard drive is worth preserving, you can contact a data recovery company to recover the data. A data recovery lab can repair or replace the damaged internal parts of the hard disk and retrieve any existing data.

A hard disk drive (HDD), commonly referred to as a hard drive, hard disk, or fixed disk drive, is a non-volatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces. Strictly speaking, "drive" refers to a device distinct from its medium, such as a tape drive and its tape, or a floppy disk drive and its floppy disk. Early HDDs had removable media; however, an HDD today is typically a sealed unit (except for a filtered vent hole to equalize air pressure) with fixed media.

Bus

In ,computer architechture a bus is a subsystem that transfers data between computer components inside a computer or between computers. Unlike a point-to-point connection, a bus can logically connect several peripherals over the same set of wires. Each bus defines its set of connectors to physically plug devices, cards or cables together.
Early computer buses were literally parallel electrical buses with multiple connections, but the term is now used for any physical arrangement that provides the same logical functionality as a parallel electrical bus. Modern computer buses can use both parallel and bit-serial connections, and can be wired in either a multidrop (electrical parallel) or daisy chain topology, or connected by switched hubs, as in the case of USB.


A control bus is (part of) a computer bus, used by CPUs for communicating with other devices within the computer. While the address bus carries the information on which device the CPU is communicating with and the data buss carries the actual data being processed, the control bus carries commands from the CPU and returns status signals from the devices, for example if the data is being read or written to the device the appropriate line (read or write) will be active (logic zero).

An address bus is a computer bus, controlled by CPUs or DMA-capable peripherals for specifying the physical addresses of computer memory elements that the requesting unit wants to access (read or write).
The width of an address bus, along with the size of addressable memory elements, generally determines how much memory can be directly accessed. For example, a 16-bit wide address bus (commonly used in the 8-bit processors of the 1970s and early 1980s) reaches across 216 (65,536) memory locations , whereas a 32-bit address bus common in PC processors as of 2004 update can address 232 4,294,967,296 locations. Some microprocessors, such as the Digital Compaq Hewlett-Packard Alpha 21264 and Alpha 21364 have an address bus that is narrower than the amount of memory they can address. The address bus is clocked faster than the system or memory bus, enabling it to transfer an address in the same amount of time as an address bus of the same width as the address.
In most microcomputers such addressable "locations" are 8-bit bytes, conceptually at least. In such case the above examples translate to 64 kilobytes (KB) and 4 gigabytes (GB) respectively. However, it should be noted that accessing an individual byte frequently requires reading or writing the full bus width a word at once. In these instances the least significant bits of the address bus may not even be implemented - it is instead the responsibility of the controlling device to isolate the individual byte required from the complete word transmitted. This is the case, for instance, with the VESA Local Bus which lacks the two least significant bits, limiting this bus to aligned 32 bit transfers.
Historically, there were also some examples of computers which were only able to address larger words, such as 36 or 48 bits long.

CPU front

1.Restart button
2.Poert button
3.OPtical media
4.Status indicator
5.Auxiliary port
6.USB port

CPU rear/back

1.Power Supply unit

2.Ps/2 ports

3.USB port

4.Parallel port

5.Serial port

6.AGP port

7.Lan port

8.Expansion slot

Basic parts of a motherboard

A.CPU slot G.PS/2 port

B.RAM socket I.IDE for FDD

C.IDE for the primary&secondary Devices J.Power terminal for mainboard

D.AGP slot K.CMOS battery

E.PCI slot L.Auxiliary ports

F.Serial & parallel port M.USB port

G.PS/2 port

I.IDE slot for FDD

J.Power terminal for mainboard

K.CMOS battery

L.Auxiliary ports

M.USB port

history of computer hardware

Computer Hardware - A History

Computer hardware has transformed in the last few decades as computers evolved from bulky, beige monsters to sleek and sexy machines. Computer Hardware – a History The dictionary defines ‘computer’ as any programmable electronic device that can store, retrieve, and process data. Computer Hardware evolved as data storage, calculation and data processing became important elements in work and life. In fact, the earliest computer Hardware is thought to be record keeping aids such as clay shapes that represented items in the real world – the early mechanics of merchants and accountants of the past. From the abacus and the slide rule came analogue and later, the electronic computer Hardware known today. A timeline of the history of computer Hardware: 1632 the first mechanical calculator was built by Wilhelm Schickard. It used cogs and gears and became the predecessor for computer Hardware. 1801 punched card technology began and by 1890 sorting machines were handling data, the first computer Hardware and installations used punched cards until the 1970s. 1820, Charles Xavier Thomas created the first mass-produced calculator. 1835, Charles Babbage described his analytical engine, which was the layout of a general-purpose programmable computer. 1909, Percy Ludgate designed a programmable mechanical computer. 1914, a central component in computer Hardware – the binary numeral system- was described by Leibniz. 1930s, desktop mechanical calculators, cash registers and accounting machines were introduced. By the 1960s, calculators advanced with integrated cuircuits and microprocessors. Digital computer Hardware replaced analogue computers. Digital computer Hardware The era of the computer as we know it today began with developments during the Second World War as researchers and scientists were spurred on by the military. 1960s and beyond ‘Third generation’ computer Hardware took off post 1960 thanks to the invention of the integrated circuit or microchip. This led to the microprocessor which in turn led to the microcomputer – computer Hardware that could be owned by individuals and small businesses. Steve Wozniak co-founded Apple Computer and is credited with developing the first mass market computer, although the KIM-1 and Altair 8800 came first. Evolution in computer Hardware After the 1970s the personal computer and evolution in computer Hardware exploded across the western world. Microsoft, Apple and many other PC companies fuelled the market and today, these companies are still striving to reduce the size and price of computer Hardware while improving its capacity.

troubleshooting and maintenance