A typical HDD has two electric motors; a spindle motor that spins the disks and an actuator (motor) that positions the read/write head assembly across the spinning disks. The disk motor has an external rotor attached to the disks; the stator windings are fixed in place. Opposite the actuator at the end of the head…
Hard Disk Drive Crash
Take the case of computer systems. We become so used to working on the computer on a regular basis that we are rarely ready to face the consequences if things go wrong. This is truer of a computer hard disk drive crash than of anything else. Hard drive malfunction can be divided into two types: one is the so called Firmware Level malfunction that can be repaired using relating software or factory commands; the other one left is the Physical Level malfunction caused by physical hard drive components damage. As to the latter Physical Level crash, the typical case in data recovery practices is that the head crash and serious platter scratches caused by direct contact between the head and the platter surface; such drives manifest themselves as undetected, staying BUSY, besides an ominous scratching sound may start to emanate from the disk. This is a serious problem. It is indicative of nothing less than a crash of the hard disk drive.
Functioning of a Hard Disk Drive
In order to understand the problem of a hard disk drive crash, it is important to first understand the mechanism of a hard drive. Only after knowing how the disk drive functions can one understand the nature of the problem.
Components
Read-Write Head: The read-write heads of the hard disk drives are those mechanisms that, as the name suggests read or write the data from the magnetic fields of the platters.
Hard Disk Platter: A hard disk platter is a circular disk within the hard disk drive. It is circular in shape and the magnetic media of the disk drive is stored on it. Generally multiple platters are mounted on a single spindle of the hard disk drive.
Lubricant Layer: This is the topmost layer of the platters and is made of a substance similar to Teflon. Carbon: There is a layer of sputtered carbon just below the lubricant layer. Magnetic Layer: This is below the layer of carbon.
Functioning
The magnetic layer of the hard disk drive stores all the data. The two layers of carbon and the lubricant like material saves this magnetic layer from coming into accidental contact with the read-write head of the disk, we can say they exist as the protection layer of the magnetic layer (of course, another important function of them is to maintain the stability of the flying read-write head)
Modern hard disk drives use one of two interfaces: IDE (ATA) – Integrated Drive Electronics (also called ST506 drives) and its variants (EIDE – Enhanced Integrated Drive Electronics, or the SCSI (Small Computer System Interface). You can tell immediately by looking at the back of the hard disk which interface is being used.
1. IDE hard disks use a 40-pin connector, and SCSI hard disks normally use either a 50-pin or a 68-pin or 80-Pin connector.
2. Note: Older MFM (MODIFIED FREQUENCY MODULATION), RLL (RUN LENGTH KIMITED) and ESDI (ENHANCED SYSTEM DEVICE INTERFACE) hard disks used two data connectors, one 34 pins and the other 20 pins.
3. The cable usually has a red stripe to indicate wire #1 and the hard disk uses markers to indicate the matching pin #1.
Led Connector: Originally, hard disks shipped with a faceplate (or bezel) on the front. The hard disk was mounted into an external hard drive bay (in place of a floppy disk drive) and an LED was visible on the front of the drive to indicate when the disk was in use. It was quickly realized that having the disks mounted internally to the case made more sense, but the LED was still desirable. So an LED was mounted to the case and a wire run to a two-pin connector on the hard disk itself. On newer systems that run with integrated IDE controllers on the motherboard, the LED is connected to a special connector on the motherboard itself.
Drive Bay: The entire hard disk is mounted into a physical enclosure designed to protect it and also keep its internal environment sealed from the outside air. This is necessary because of the requirement of keeping the internal environment free of dust and other contamination that could get between the read/write heads and the platters over which they float, and possibly lead to head crashes.
DRIVE BAYS are where internal hard drives are mounted inside the PC. They come in internal and external versions, based on whether they allow access from the exterior of the case, and also in two standard sizes: 5.25″ and 3.5″.
Now, we have rough understanding of the HDD components now and how these parts work in architecture. But you may find the importance of the microprogram inside the HDD. No matter how precise the HDD design, they are a stack of meaningless mechanical parts.
Hard disk drives use a standard, 4-pin male connector plug that takes one of the power connectors coming from the power supply. This keyed, 4-wire plastic connector provides +5 and +12 voltage to the hard disk.
All modern hard disks are made with an intelligent circuit board integrated into the hard disk unit. Early hard disks were virtually all of the control logic for controlling the hard disk itself was placed into the controller plugged into the PC; there were little smarts on the drive itself, which had to be told specifically how to perform every action.
As newer drives were introduced with more features and faster speed, this approach became quite impractical, and once electronics miniaturization progressed far enough, it made sense to move most of the control functions to the drive itself.
The most common interface for PC hard disks is called IDE, which in fact stands for Integrated Drive Electronics. This name is something of a misnomer today. When it was introduced, IDE was distinguished from the other interfaces of the day by having the integrated electronics on the drive, instead of on the controller card plugged into the system bus like older interfaces. However, the term really refers to where the control logic is and not the interface itself, and since all hard disks today use integrated electronics the name doesn’t mean anything any more, despite the fact that everyone continues to use it. The other popular PC hard disk interface today, SCSI, also uses drives that have integrated controllers. The more correct name for the IDE interface is AT Attachment or ATA.
The logic board of a Cheetah 10,000 RPM 36 GB hard disk drive.The main interface and power connectors are on the right-hand side;auxiliary connectors on the bottom and left side. The bottom of the spindlemotor protrudes through a round hole made for it in the circuit board.
What’s the relationship between PCBA and Control Circuitry? Let me give an example. The electric current is like Blood and the Control Circuitry is like the blood vessel distributing on the HDD, and the PCBA is like the brain to process and give orders to particular parts.
The drive’s internal logic board contains a microprocessor (inside main chip) and internal memory (RAM chip), and other structures and circuits that control what happens inside the drive.
In many ways, this is like a small embedded PC within the hard disk itself. The control circuitry of the drive performs the following functions (among others):
1. Controlling the spindle motor, including making sure the spindle runs at the correct speed.
2. Controlling the actuator’s movement to various tracks.
3. Managing all read/write operations.
4. Implementing power management features.
5. Handling geometry translation.
6. Managing the internal cache and optimization features such as pre-fetch.
7. Coordinating and integrating the other functions, such as the flow of information over the hard disk interface, optimizing multiple requests, converting data to and from the form the read/write heads require it, etc.
8. Implementing all advanced performance and reliability features.
You may think that the Control Circuitry is not so important. The reason is that the quality or optimization level of the control circuitry doesn’t manifest itself as a single, simple specification. You can’t easily compare the circuitry of five different drive families. Most hard disk manufacturers provide very little information about the “guts” of the logic board, and even if they did, most people wouldn’t know what to do with the information.
However, the control circuitry of the drive is underrated and misunderstood, even by those interested in hard disk performance issues.
In fact, differences in control circuitry account for part of the differences in some specifications. This is probably most true of seek performance, Beyond this, you can’t really tell much about what’s inside the circuitry. However, if you use two different drives that have very similar specifications and run on the same interface on the same PC, but one just “feels faster” than the other, differences in their internal circuitry may be part of the answer.
Since digital information is a stream of ones and zeros, hard disks store information in the form of magnetic pulses. In order for the PC’s data to be stored on the hard disk, therefore, it must be converted to magnetic information. When it is read from the disk, it must be converted back to digital information. This work is done by the integrated controller built into the hard drive, in combination with sense and amplification circuits that are used to interpret the weak signals read from the platters themselves.
In short, the disk controller consists of a ROM that embedded some disk commands to translate and implement some write and read orders from a PC, it is like a disk controller chip, and a little glue to make it all work.
I used to imagine that a Hard disk controller is a talented translator who lives in a chip of PCB, translating between the magnet signal of ones of HDD and zeros and commands from PC.
Modern disk controllers are integrated into the disk drive. For example, disks called “SCSI disks” have built-in SCSI controllers. In the past, before most SCSI controller functionality was implemented in a single chip, separate SCSI controllers interfaced disks to the SCSI bus.
The most common types of interfaces provided nowadays by a disk controller are ATA (IDE) and Serial ATA for home use. High-end disks use SCSI, Fibre Channel or Serial Attached SCSI.
The spindle motor, also sometimes called the spindle shaft, is responsible for turning the hard disk platters, allowing the hard drive to operate. The spindle motor is sort of a “work horse” of the hard disk, like a heart of human, it give the motivity of power to the HDD. It’s not flashy, but it must provide stable, reliable and consistent turning power for thousands of hours of often continuous use to allow the hard disk to function properly. In fact, many drive failures are actually failures with the spindle motor, not the data storage systems, such as that the motor bearing seizure, Motor not spin.
The spindle motor has several important commitments placed upon it. First, the motor must be of high quality, so it can run for thousands of hours, and tolerate thousands of start and stop cycles, without failing. Second, it must be run smoothly and with a minimum of vibration, due to the strict tolerances of the platters and heads inside the drive. Third, it must not generate excessive amounts of heat or noise. Fourth, it should not draw too much power. And finally, it must have its speed managed so that it turns at the proper speed, neither faster nor slower.
I’ve found that the weather is one of the factors which effect the lifetime of HDD. From some customers from Africa, there are more haunted by the Motor stuck problems than any other places. For some HDD used on server have more demands on the tolerance and quality, they are supposed to be work at 7X24 a week.
To meet these demands, all PC hard disks use servo-controlled DC spindle motors. A servo system is a closed-loop feedback system; this is the exact same technology as is used in modern voice coil actuators. Let’s see how servo systems work in detail. In the case of the spindle motor, the feedback for the closed-loop system comes in the form of a speed sensor. This provides the feedback information to the motor that allows it to spin at exactly the right speed.
All hard disk spindle motors are configured for direct connection; there are no belts or gears that are used to connect them to the hard disk platter spindle. The spindle onto which the platters are mounted is attached directly to the shaft of the motor. The platters are machined with a hole at the exact size of the spindle, and are placed onto the spindle with separator rings (spacers) between them to maintain the correct distance and provide room for the head arms. The entire assembly is secured with a head cap and usually, lots of small Torx screws.
! By design, TORX head screws resist cam-out better than Phillips head or slot head screws. Where Phillips heads were designed to cause the driver to cam out, to prevent over-tightening, TORX heads were designed to prevent it. The reason for this was the development of better torque-limiting automatic screwdrivers for use in factories. Rather than relying on the tool slipping out of the screw head when a torque level is reached, and thereby risking damage to the driver tip, screw head and workpiece, the drivers were designed to achieve a desired torque consistently. Camcar LLC claims this can increase tool bit life by ten times or more.
One important quality issue that has become a focus of attention with newer hard disks is the amount of noise, heat and vibration they generate. The reason for this becoming more of an issue is the increase in spindle speed in most drives. On older hard disks that typically spun at 3600 RPM, this was much less of a problem. Some newer drives, especially 7200 and 10,000 RPM models can make a lot of noise when they are running. If possible, it’s a good idea to check out a hard disk in operation before you buy it, to assess its noise level and see if it bothers you; this varies greatly from individual to individual. Heat created by the spindle motor can eventually cause damage to the hard disk, which is why newer drives need more attention paid to their cooling. Newer high-speed drives almost always run cooler and quieter than the first generation of drives at any new spindle speed. It can be painful to be a pioneer;
We often call the Head-Actuator Assembly as head stacks or only heads for short. In fact, we make a mistake in some way. Let’s take a look at a head-actuator Assemble on the flowing photo:
Mostly, each platter is accessed for read /write operations using two read/write heads, one mounted on the top of the platter and another on the bottom. These heads are mounted onto arms that allow them to be moved from the outer tracks of the hard drive to the inner tracks and back again. The arms are controlled using a device called an actuator that positions the arms to the appropriate track on the disk. The read/write heads don’t touch the platter when the platter is spinning at full speed; instead, they float on an extremely thin cushion of air (10 millionths of an inch, Winchester disk drive). That’s why power surge may cause Head crash and platter scratch due to the fast rotating rolling of platters.
Notice: In 1973, IBM introduced the IBM 3340 “Winchester” disk drive, the first significant commercial use of low mass and low load heads with lubricated media. All modern disk drives now use this technology and/or derivatives thereof. Project head designer/lead designer Kenneth Haughton named it after the Winchester 30-30 rifle after the developers called it the “30-30” because of it was planned to have two 30 MB spindles; however, the actual product shipped with two spindles for data modules of either 35 MB or 70 MB.
How they work?
The hard disk platters are accessed for read and write operations using the read/write heads mounted on the top and bottom surfaces of each platter. Obviously, the read/write heads don’t just float in space; they must be held in an exact position relative to the surfaces they are reading, and furthermore, they must be moved from track to track to allow access to the entire surface of the disk. The heads are mounted onto a structure that facilitates this process. Often called the head assembly or actuator assembly (or even the head-actuator assembly), it is comprised of several different parts.
The heads themselves are mounted on head sliders. The sliders are suspended over the surface of the disk at the ends of the head arms. The head arms are all mechanically fused into a single structure that is moved around the surface of the disk by the actuator. (Sort of like “the wrist connected to the hand”, why I say it is a hand because it is very skillful and ingenious and the upper site is Arm: D).They play an important role in the function and performance of the drive. In particular, advances in slider, arm and actuator design are critical to improving the seek time of a hard disk.
Each track is further broken down into sectors. A sector is normally the smallest individually-addressable unit of information stored on a hard disk. Each sector of data on the hard disk contains 512 bytes, or 4,096 bits, of user data (1 byte=8 bits it is octal). In modern drives the larger outer tracks hold more sectors than the smaller inner ones. All information stored on a hard disk is recorded in tracks. The tracks are marked by number, starting from zero, starting at the outside of the platter and increasing in number as you go in.
The first PC hard disks typically held 16 sectors per track. Details as below from Seagate
Capacity:Speed:Average Read Time: Cylinders:Heads:Sectors: 85.7 MB3500 rpm16 ms74814 (Physical Only 2 Heads)16
Resource: Examples: 16 (e.g. the st9100ag), 17 (e.g. the st325ax), 24 (e.g. the st9190ag), 27 (e.g. the st280a), 28 (e.g. the Maxtor 8051A), 29 (e.g. the st1162a), 32 (e.g. the st9051a), 34 (e.g. the st3195a), 35 (e.g. the st3283a), 36 (e.g. the st1239a), 38 (e.g. the st3211a), 47 (e.g. the st9150ag), 50 (e.g. the st3291a), 51 (e.g. the st9385ag), 52 (e.g. the st9240ag), 53 (e.g. the st3271a), 55 (e.g. the st2274a), 56 (e.g. the st2383a), 59 (e.g. the st9550ag), 60 (e.g. the st9300ag), 61 (e.g. the st1401a), 62 (e.g. the st3385a), 63 (e.g. the st3270a).
(Please go to Seagate website to get the details of above HDD.)
A sector includes only 512 Bytes?
In addition to these bits (512 Bytes of user data), an additional number of bits are added to each sector for the implementation of error correcting code or ECC (sometimes also called error correction code or error correcting circuits). These bits do not contain user data; rather, they contain information about the data that can be used to correct any problems encountered trying to access the real data bits.
Block Mode: More than one sector can be transferred on each interrupt notification. Newer drives allow you to transfer as many as 16 or 32 sectors at a time. These sectors are known as Clusters. On some systems you will find an option in the system BIOS called block mode. You may set it on BIOS.
Block mode is a performance enhancement that allows the grouping of multiple read or write commands over the IDE/ATA interface so that they can be handled on a single interrupt.
Example of a BIOS option for the IDE Block Mode feature (boxed in red)
Platters in physical
The physical material of Platters: Aluminum alloy comprises the physical material of the platter. It is rigid, easy to work with, lightweight, stable, inexpensive and readily available. The speed that the platters spin is increasing to store data much quicker and in intensive tracks, it is creating more demands on the platter material itself. That’s why the first glass Platters of IBM HDD failed to dominate the market;
Media Layer: The physical material (Aluminum alloy) of which the platters are made forms the base upon which the actual recording media is deposited. The media layer is a very thin coating of magnetic material which is where the actual data is stored, typically only a few microinches in thickness. The media layer is usually comprised of a special alloy. That’s why the data will lose or inaccessible by ages of using. It is because the thin media layer become dull or damaged and can’t react the signals from the HDD or commands from a PC;
Does it make any sense to wash Platters with distilled water or alcohol?
You must laugh at my silly question. But it happened, someone told me before that He did wash the platters with pipe water because there are many fingerprints on them, and, huh, according to his words, he had fixed it and that drive got working.
Can we put the hard drive near with some magnetic materials?
People put the hard drive in some antistatic storage and they avoid to put their credit cards and other magnetic cards together.
Protective Layer: The surface of each platter is normally covered with an extra-thin, protective, lubricating layer, on top of the magnetic media layer itself. This material is used to protect the disk from damage caused by accidental contact from the heads or other foreign matter that might get into the drive. That’s why you can use your HDD to store data for years, not for a couple of months;
Platters in Logically
Platters Divisions: The platter is divided into Tracks and Sectors and is read by Zone Recording or Clusters.
Tracks:
Platters are organized into specific structures to enable the organized storage and retrieval of data. Each platter is broken into several thousand tracks, which are tightly-packed concentric circles. (These are similar in structure to the annual rings of a tree.,see the circle in red of the Picture).
But, you will find that the ones on the outside of the platter are much larger than the ones on the inside–typically double the circumference or more. Since there is a constraint on how tight the inner circles can be packed with bits, they were packed as tight as was practically possible given the state of technology, and then the outer circles were set to use the same number of sectors by reducing their bit density. This means that the outer tracks were greatly underutilized, because in theory they could hold many more sectors given the same linear bit density limitations.
To eliminate this wasted space, modern hard disks employ a technique called zoned bit recording (ZBR), also sometimes called multiple zone recording or even just zone recording. With this technique, tracks are grouped into zones based on their distance from the center of the disk, and each zone is assigned a number of sectors per track. As you move from the innermost part of the disk to the outer edge, you move through different zones, each containing more sectors per track than the one before. This allows for more efficient use of the larger tracks on the outside of the disk.
