BIOS (Basic Input Output System) is the way in which a computer can start up and load up the operating system. One of the pieces of information it stores is information about the boot device, for the purposes of this text this is assumed to be a mechanical hard disk. Mechanical hard disks are the most popular type of storage technology in the world but eventually they will fail.
WHY CANT THE COMPUTER SEE THE DISK?
Even though the disk is spinning and is correctly attached to the computer when disks fail in a specific way the BIOS will not be able to detect the disk and therefore will not be able to boot the operating system. Disks which have failed in this manner are known to have or be developing many bad sectors; hard disks are split into sectors to store the data on their platters (typically these sectors are 512 bytes each but there are exceptions). Modern hard disks have the ability to remap bad sectors to prolong their life but this is not a fail safe against failure, every mechanical hard disk will fail in this way if it does not fail in another way first, it is simply a case of when not if. The life expectancy can vary from disk to disk, some fail after a few weeks others can last years and years, even decades. When they break down to a certain extent the BIOD is not able to detect the disk and as such doesn't show that a disk is present.
CAN I GET THE DATA BACK MYSELF?
Without the assistance of a data recovery laboratory the chances of you getting your data back is slim at best. There are some tricks that could be applied in the case of a hard disk that has failed in this manner although in most instances this will not result in a full recovery and could cause more damage to the data.
HOW DO YOU GET MY DATA BACK?
In a nutshell several methods are used to recover data from disk which have failed in this manner, one in particular being the use of specialised hardware that reads data from the disk is a different and much less demanding way in which a normal computer and operating system does. This process is something which varies from disk to disk, each failed disk is unique. The recover involves a multi pass read process which is unique in how it reads each sector and how it deals with bad sectors i.e. initially only sectors which are reading normally are read; the subsequent reads are carried out in their own unique way. It is also necessary to configure the recovery process for specific manufacturers whilst also bearing in mind the possibility for a more severe disk failure such as head failure during the recovery process.
Whilst normally considered to be a less complicated failure it is by no means unusual for disks that have failed in this way to take longer to recover then one that has sustained a mechanical issue. Hard disks have many millions of sectors but it only takes a small number to stop a disk working.4 Years, 4 Months, 1 Week, 1 Day, 18 Hours, 4 Minutes ago.