Posts Tagged ‘hdd Components’

Platter Scratch Repairing

December 12th, 2008 Comments off

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.

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.

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)

Data Interface Connector or Card

December 11th, 2008 Comments off

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 Drive Power Connector

December 11th, 2008 Comments off

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.

PCBA, control circuitry (Printed Circuit Board Assembly)

December 11th, 2008 Comments off

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.

Hard Disk Drive Controller

December 11th, 2008 Comments off

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.