Computer disk drives have come a long way since they were invented in the 1950's. The technology has been improved remarkably over the years. However, the fundamental principle behind how hard disks work is basically the same. A platter with a magnetic surface spins while an electronic component called a "head" is positioned over areas of the platter to read and write data. It is very similar to the old phonograph with an arm and a needle picking up music from the tracks on the record. Hard disks spin much faster than a phonograph record and the head does not actually touch the platter. However, the head is positioned very close to the spinning platter. Early hard drives would frequently suffer a mechanical failure that would allow the head to actually touch the surface of the spinning platter, which would cause a horrendous noise as the head was destroyed while it cut grooves into the platter. The term "crash" was a reference to the read/write head physically crashing into the rapidly moving platter.
Hard disk engineers now stack multiple platters together with read/write heads on both sides. Modern hard drives are smaller, they spin faster, the heads are closer, and there are many more heads in each drive. The electronics are also more sophisticated because the data is packed much closer together, which requires much more precision in the mechanism which positions the heads over the data. Modern drives have been engineered for greater reliability; for example, all hard disk devices are now sealed to prevent dust or foreign particles from getting between the heads and the platters, which was found to be the cause of many crashes in the early models.
Even modern hard disk drives occasionally suffer from the traditional crashes as described above, although less frequently on a per-drive basis. Instead of a loud crashing noise, you may hear a grinding or whining sound when a hard drive head actually comes into contact with a platter. While this sound is not as loud and dramatic as the early hard drive crashes, the sound is still considered quite disturbing to most of us. It's not the same disturbance as a car crash, but the sound of permanent data loss is no laughing matter for must of us.
These days, every hard drive failure is called a hard drive crash. There are many reasons why a drive will fail. Most of the reasons are electrical rather than mechanical. Instead of hearing a grinding sound, you may hear a clicking sound. This usually means that the actuator that positions your read/write heads is thrashing back and forth for some reason; perhaps it is malfunctioning or otherwise cannot find the data it is seeking.
Hard disk drives do not always fail suddenly. Sometimes there are signs that your hard drive is failing. You might notice that your computer has become very slow at opening an application that usually opens fast. Or you may find files or entire folders are missing. You may also find that it takes several tries to start your computer. These signals don't definitively indicate a hard drive failure is imminent. There are other causes for the same same symptoms. If you are lucky your computer or hard drive will give you signs that your hard drive is failing and you will have a chance to backup your files or replace the drive before total failure. However, more times than not, your hard drive will die unexpectedly and you will have no opportunity to save anything.
Fortunately, there are services that can recover most data when a hard drive fails. These services use sophisticated equipment and skilled technicians to disassemble your hard drive and extract any usable data remaining on the platters. The recovery operations are performed in clean rooms similar to the operating room in a hospital. These facilities are expensive to setup and operate so you will pay a hefty price to have your data recovered by one of these services. Most of us will consider the data lost and suffer the consequences before we pay for a recovery service.
You are well advised to backup your data frequently so that you will be prepared when your hard drive eventually fails. The cost of a single data recovery can easily exceed the fees of an online backup service for a few years. Backing up your data will not only save you money, but also save you time and heartache.