Everybody who uses computers regularly is likely to experience either data loss or a failed hard drive (or both, which is more common than you think!) at some time. Hard drives store data in "sectors" (if using the FAT16 file system, used with much older operating systems such as DOS) or in "clusters" if used with FAT32 or NTFS file systems. Hard drive recovery is possible if you catch a failing hard drive early enough before it fails completely.
Hard drive maintenance is important for maintaining a hard drive's longevity and it's up to you to ensure you do some hard drive maintenance regularly (once per week or month at a minimum) - you'll be surprised how much upset this can save you later down the line if you persistently stick to this maintenance regime - set it up to do it at a late time if you leave your PC on at night - you won't even notice it then.
Hard drive maintenance can be broken down into two distinct functions: checking the disk occasionally for failed clusters and keeping data organized on the drive so that it can be accessed quickly. Having data available in the right place on the hard drive makes your hard drive's job so much easier and therefore it doesn't need to work as hard to provide the data that your operating system needs - thus prolonging its working life.
Hard drive problems fall into three broad categories:
• Installation;
• Data corruption and;
• Dying hard drive;
Power surges, accidental shutdowns, corrupted installation media and viruses are among the causes of corrupted data in individual sectors / clusters. These errors usually show while Windows is running. If core boot files become corrupted, you may see text errors such as "Cannot find COMMAND.COM," "Error loading operating system", or "Invalid BOOT.INI".
Older systems may generate a sector not found error. The first fix for any of these problems is to run an error-checking utility, such as Spinrite from Gibson Research. If you get the "Trying to recover lost allocation unit" error, this means that the drive has bad sectors. If this happens to you, then it's definitely time to start thinking about replacing your failing hard drive - and quickly.
If you get an error which says that a particular file is missing for Windows to run or function properly,then to replace a single corrupt file, you must know the location of the numbered Windows CAB (cabinet) file that contains the file you need and how to extract the file from the CAB file. Use the EXPAND program with Windows 2000/XP to get a new copy of the desired file from the CAB file on your installation disc, which you should have for installing Windows in case of emergency. EXPAND searches all CAB files to find the file you specify, and then expands it and places it in the C: folder. To find out more on how to use EXPAND, take a look on a Google search.
Thankfully for the uninitiated, almost all hard drives today have a built-in error correction code (ECC) that constantly checks the hard drive for bad sectors / clusters. If the drive detects a bad sector as it operates, it then marks the sector as bad in the drive's internal error map so that it's invisible to the operating system and therefore no data gets written there. However, if the ECC finds a bad sector with data already within it, you will get a corrupted data error when the computer attempts to read the bad sector.
If a hard drive is truly physically damaged, it simply cannot be fixed, although you may be able to rescue (some, if not all) data from it before it dies completely.
In fact, I learnt a valuable lesson many years ago - ALWAYS back up your important / critical data at regular intervals! How you do this is completely upto you. There are many third party software packages out there to use - my preference is to take an image of the drives / partitions that operate within my computer and make incremental backups once per week or month, overwriting the previous version so it's a rolling, updated copy (I also save copies of these images to two separate hard drives for extra peace of mind). In fact, I use a free piece of software called DriveImage XML which works perfectly fine for my own personal needs.
However, if you want something that's more commercial, then you can try Norton Save & Restore (PC) which is built on Norton's extremely effective and successful "Ghost" data backup and recovery software.
Physical problems with hard drives manifest themselves in two ways:
• Either the drive works properly but makes a lot of noise, or;
• The drive seems to disappear from your BIOS / Windows operating system
If you hear a continuous high-pitched squeal, or a series of clacks, a short pause, and then another series of clacks, or even a continuous grinding or rumbling, your hard drive is quite frankly, about to die. Whatever you do next, make sure you back up your critical data and replace the drive as soon as you can. If the drive that contains your operating system disappears, the system will lock up or you will get the error message "No Boot Device Present" when you try to reboot. If the problem is with a second drive, it will simply stop showing up in My Computer.
If your drive makes noise or disappears, first run the BIOS to see if it autodetects the drive. If it does, the drive probably doesn't have a physical problem just yet. If autodetect in BIOS fails, shut down the system and remove the ribbon / IDE cable, but leave the power cable attached. Restart the system and listen to the drive itself. If the drive spins up, the drive is getting good power, which usually means the drive is at least good for now.
Next, check for an unplugged power cord or incorrectly set jumpers. If the drive doesn't spin up, try another power connector. If it still doesn't spin up and you've triple-checked the jumpers and ribbon cable, you have a problem with the onboard electronics of the hard drive and the drive is dead. I really hope you backed up your data as I stated earlier!
The base storage area for hard drives is a sector, which can store up to 512 bytes of data. If a file is smaller than 512 bytes and does not fill a sector, the rest of the sector remains unused as only one file can reside in any one sector. If a file is more than 512 bytes, the file is split into pieces with each piece residing in different sectors. If the sectors containing all the pieces of a single file are not contiguous, the file is said to be fragmented - hence the reason why we must use the "Defragmenter" program in Windows or another third party tool to do this (sometimes) time-consuming job. In fact, I use another free program called Defraggler, which works much quicker than Windows own Defragmenter program. Try it - I hope you find it's much quicker and equally as effective!
Since FAT16, a cluster rather than a sector is the basic unit of storage. Unlike sectors, the size of a cluster is not fixed; it changes with the size of the partition. Because FAT16 still supported only a maximum of 64-K storage units, the formatting program set the number of sectors in each cluster according to the size of the partition.
After the format program creates the FAT (File Allocation Table), it tests each sector and places a special status code (FFF7) in the FAT for any bad sectors so they won't be used. Good sectors are marked with 0000. When an application saves a file (such as a spreadsheet or Word document), the OS starts writing the file to the first available cluster marked as good. If the entire file fits in the cluster, the OS (operating system) places the end-of-file marker (FFFF) in the cluster's status area.
If the file does not fit entirely in a single cluster, the OS searches for the next available cluster. Once found, the location of this next available cluster is written to the status area of the preceding cluster holding a piece of the file, and the OS writes the next 512 bytes of the file in the available cluster. This continues until the file has been completely written and the final cluster in the chain receives the status code FFFF in the FAT. After saving the entire file, the OS lists the filename and starting cluster in the file's folder.
However, therein lies a problem - as a file is split across multiple non-contiguous clusters, the file becomes fragmented and fragmentation slows read / write access as the operating system has to piece together the many fragments of the file to load it into memory for use within an application (for example) or save it when required too. Every version of Windows, except NT, comes with a disk defragmenter program that re-organises the clusters of hard drive data, so files are stored wherever possible in contiguous clusters. FAT32 was introduced with Windows 95 OS2.
FAT32, which uses 32 bits to describe each cluster, supports partitions up to 2 terabytes. FAT32 creates smaller clusters and therefore stores files more efficiently than FAT16 but the New Technology File System (NTFS) was introduced with Windows NT and has gone through several versions, with the most recent version, used since Windows 2000, being referred to as NTFS 5. NTFS does not use a file allocation table like FAT16 or FAT32, but instead uses a master file table (MFT).
NTFS offers several major improvements over FAT, including redundancy, security, compression, encryption, disk quotas, and cluster sizing. A backup copy of the most critical parts of the MFT is stored in the middle of the disk, where it is less likely to become damaged and in turn, means it has an extra backup element over FAT32, which if the MBR (Master Boot Record) is damaged, you may well lose your data altogether as it does not store a backup of the MBR anywhere else on the drive.
Now that you understand how a hard drive reads and writes data and the associated file systems that were (and are) common in PC's today, such as FAT32 and NTFS, you are now aware of the software and physical symptoms that can become apparent when a hard drive is failing and if recognised early enough, means you may be able to back up any vital or crucial data before it's too late.
Phil Garvey [manchester-computer-repairs.co.uk bad domain] Manchester Computer Repairs
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