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Imagine this: you're busy working on your computer and need to access documents saved on your external hard drive. You connect it, get ready to find your data, and...nothing happens. Your hard drive isn't working. Uh oh. Before you panic, there are several things you can try on your own before calling in the pros.
Data loss can be due to a number of factors, but two are the most common. The first (and easiest to resolve) is software related. You've accidentally deleted an important folder and emptied the recycle bin, or gone and formatted the wrong drive by mistake. The second—and probably most common—cause of data loss is a fault with the hard drive itself. Given the complexity of modern drives it's no wonder that somewhere along the line something will go wrong. When the drive suffers from some form of failure there's often little that you can do yourself to get the data back—professional data recovery services are usually required. However,there are certain failures that you can attempt to resolve yourself.
Recover Your Data with Software
When dealing with a software data loss, the first and most important thing to keep in mind isnot to work with the drive in question. Every second that the drive is connected to a running system is a second that you lose your chances at recovery. Your operating system is reading and writing to your drive constantly, whether you're actively doing something or not. Now that your system is seeing the deleted data as ‘free space' it will happily overwrite this area—along with your chances of recovery.
Shutdown the machine connected to the drive you've deleted data from. Now that your drive is ‘safe' you can make a clone of the drive and attempt the recovery from the clone. There are a number of ways to clone the drive, some easier and quicker than others.
Scan the clone with a few different recovery programs. There are numerous options here, both free and paid-for packages are available. Recuva is a good free option, while Zero Assumption Recovery works well if you want to splash out a few dollars.
Pictured: The basic components of a hard drive with top cover off and PCB removed.
Recover Your Data with Hardware
Having covered the ‘deleted data' section of data recovery is all good and well, but what happens if your drive is not even being detected by your machine? Or your machine can see the drive, but just hangs when you try to access it? What about if the drive is completely dead and won't even spin up? Let's briefly cover the main components of a drive, see which components can fail, and what symptoms each failure might exhibit.12
PCB: This is the (often green) circuit board attached to the bottom of your drive. It houses the main controller (the equivalent of your computer's CPU) along with many other electronic controllers. This is the interface that turns your 0s and 1s from the platter into usable data that your computer can understand.
Platters: Your drive contains one or more thin, circular platters. These spin around at anywhere between 5,900rpm to 7,200rpm on consumer drives and are the media that actually store your data. Made of glass or some form of alloy and coated with a magnetic layer, they can store anything up to 4TB of data.
Head assembly: Data from your drives' platters is read by means of a series of read and write heads. While in operation, these heads are not actually in contact with the surface of the platters. In fact, they ‘fly' nanometers above the surface of the disk, reading and writing data. Typically a drive will have 2 heads per platter, so a large capacity drive with 3 platters will be paired up with 6 heads, one for each side of each platter. If these heads fail physically or the drive is dropped or knocked over, the drive can experience a ‘head crash' where the heads no longer fly over the platters, but instead make contact with the surface and destroy your data at a few thousand revolutions per minute.
Firmware: Your drive runs its own mini operating system in order to deal with all of the data and operations required to access it. Most of this firmware is stored on the platters. A small portion is stored on the PCB, which is required when the drive starts up. Firmware can go wrong, leading to inaccessibility of your data. Unfortunately hard drive firmware is not similar to your mobile phone or tablet—you cannot just update or reflash it. Each drive has its own unique modules and parameters and is highly complex in nature.
Now that we understand the basic components of a hard drive let's look at some common failures and symptoms you might experience, determine which component could be causing the problem, and see if we can tackle some of these problems DIY style.
If Your Drive Isn't Spinning Up At All
This is the one instance where you have a relatively good chance of resurrecting your drive if you're prepared to put in some time and effort. If the drive does absolutely nothing when you apply power to it (no noises at all), it is 99% a PCB problem. With older drives, you could sometimes find a matching PCB from another matching drive, swap it over, and voila. However, on new drives, technology and architecture have changed and each drive contains microcode unique to the drive it's attached to. Simply swapping the PCB with a matching, working equivalent has almost no chance of working and can be outright dangerous to your data.
There are two main causes of failure here, either a TVS diode (fuse) has shorted due to overvoltage, or a vital component on the PCB has failed. Hard drive PCBs often have two TVS diodes which act as fuses to protect your drive in the event of a power spike. There will most likely be two of these: one for the 5v and one for the 12v rail. If you accidentally plugged in the wrong power adapter to your external drive, or you experienced a power surge, a TVS diode might have sacrificed itself. If the shorted TVS diode is the only casualty and the rest of the PCB components are OK, then simply removing the shorted diode is enough to bring the drive back to life.
You can test this with a multimeter—if the diode reads zero ohms, or close to it, then it has indeed shortened. When shorted these diodes often have a noticeable burnt smell and might have visible burn damage. Note that when a TVS diode is removed the drive is no longer protected, so ensure that the power supply you connect to the drive is correct and healthy.
Pictured: A PCB with the TVS diodes highlighted3
If the TVS diodes don't smell burnt and show the correct digits when measuring them, then the problem is the PCB itself. A replacement PCB is required, but not just a straight swap. There is an 8 pin ROM chip on most PCBs that contains unique firmware info that is required to start up the drive. This needs to be moved from the old PCB to the new in order for the replacement to work. Some hard drives, especially Western Digitals, do not have this 8 pin chip—the firmware is stored in the main controller which is virtually impossible to move.
If you want to replace the PCB then you'll need to fine a matching replacement and have the ROM chip moved. There are many online providers that will sell you a matching PCB. Some of them even offer to move the ROM chip for you, saving you the hassle of soldering and possibly damaging the chip. If the PCB was the only damaged component and the drive's internals are OK, then after the replacement and ROM swap, your drive should be up and running again. Another PCB-related item to check are the head contacts. Sometimes they corrode with time, but are easily cleaned with a rubber eraser.
Pictured: The contacts on a PCB can cause problems when they become tarnished like this.
If Your Drive Is Spinning Up and Making Clicking Noises
This is a serious failure and indicates a failed head or heads. It could also mean that your drive has suffered from platter damage if a head crash has occurred. Either way, this is a job for the pros. The drive will need to be opened in a clean room environment in a lab and a replacement head assembly fitted in order to try and recover your data. If your drive is clicking, it's best power it off and leave it in this state until you can send it to a professional recovery company. Powering it up in this state could degrade the disk further, to the extent that it's no longer recoverable.
Pictured: A hard drive that experienced a head crash and made a deep scratch. This can render a drive unrecoverable.
4If Your Drives Spins Ups and Is Detected by Your Computer, But Hangs When You Try to Access It
This usually means that the magnetic media is degraded. Basically, there are a large amount of bad sectors that the drive is trying to read, failing to do so, and hanging. This is a common problem that occurs over time and can be worked around, but only with professional data recovery equipment, more specifically a hard imager. If you look at the SMART values of the drive you'll notice and large amount of reallocated sectors to confirm your suspicions. If the data is important then send it off to the pros.
If you want to have a crack at it yourself (and risk making the problem worse or losing your data altogether) then you can try a software imager that can work around bad areas. Seeing that software commands ultimately goes through the BIOS, the effectiveness is limited. The best option if you want to go this route is a free Linux application called dd_rescue. It can skip bad areas and image in reverse.
If Your Drive Makes a Beeping Sound When You Power it Up
The beeping sounds you are hearing is the motor trying to spin the drive up and failing to do so. This is caused by one of two things, both serious mechanical failures. The most common is what's known as stiction. The heads of your drive park either in the center or on a ramp at the edge of the drive when not in use. Remember, the heads don't make contact with the data area of the platters, they fly just above. Sometimes, the heads can fail to park properly and the platters stop spinning with the heads still over the data area. Because of the extremely smooth surfaces of both the platters and heads, they literally stick to each other, hence the name stiction. The drive needs to be opened up in the lab, heads carefully removed and most likely replaced, definitely not a DIY job.
Pictured: The head assembly with drive turned off and heads in the parked position. With stiction, they would be stuck somewhere on the platters.
The other cause could be seizure of the motor spindle. This is the spindle around which the platters rotate. It can become seized if the drive suffers a hard knock or drop. It's not a particularly common fault, except for Seagate drives as they have a particularly fragile spindle. There are two ways for this problem to be resolved, both of which require pro intervention. Either the spindle can be replaced or the platters are moved to a new hard drive casing along with heads, PCB, the works.
If Your Drive Sounds Normal but is Not Detected, or is Detected as the Wrong Capacity
This normally indicates a problem with some area of the firmware. Either it's not being read properly which could actually be head problem, or there is some corruption that needs to be resolved. A few years back there was a well-known bug with Seagate 7200.11 drives with firmware version SD15 known was the BSY bug. Googling this provide a wealth of info of the huge amount of failures were caused by this firmware glitch. There was a DIY solution for this particular problem, but with today's drives there is nothing that the end user can do but to send your drive in for professional help.
So, there are a few instances where you can attempt to recover your own data. If you've accidentally deleted your data then you might be in luck. If the drive is completely dead and won't even power up then you could go the DIY PCB route if you wish to tinker. Other than that, if your drive is making unusual noises or acting in a peculiar manner, you'll need to hand it over—together with some hard earned cash—to a data recovery professional. Remember,ANY attempts at data recovery are risky. If the data is important, take it directly to the professionals.
Nick Parsons is the Founder of SouthBit Data Recovery, leading data recovery service provider in South Africa. He founded SouthBit after receiving his honors degree in digital forensics. SouthBit Data Recovery rovides recovery services to all media including hard drives, SSD drives, and RAIDs. People can get more info on how their hard drive works by viewing their site at here.
Source:http://www.stumbleupon.com/
Professor John Mauchly, ditemani oleh J. Presper Eckert dari University of Pennsylvania mengepalai tim pembuatan ENIAC. Anggota tim lainnya adalah Bob Shaw, Chuan Chu, Kite Sharpless, Arthur Burks, Harry Huskey, Jack Davis, dan Iredell Eachus Jr. Sampai akhirnya selesai dibuat pada tanggal 14 Februari 1946, total dana yang dihabuskan mencapai 486.804, 22 dolar AS.
Pada perjalanannya, ENIAC cukup rumit untuk ditangani. Sebagai contoh, ketika terjadi kerusakan pada salah satu tabung kedap udara yang terpasang di ENIAC, teknisi harus memeriksa keseluruh 19 ribu buah tabung untuk mencari tabung mana yang tidak berfungsi.
