Some hard drive crashes are random but most are predictable. That’s because almost all modern drives implement a monitoring technology called S.M.A.R.T (Self Monitoring Analysis and Reporting Technology) that continuously passes readings on the hard drive condition to the computer’s BIOS. Up to 30 drive parameters can be monitored by SMART including read and write error rates, seek error rate, spin up time, temperature and more.
To analyze this mass of data you need a special hard disk health monitoring program. Such programs can give you valuable advance warning that your hard drive is about to fail. This should give you time to backup your critical data and start looking for a replacement drive.
Most of these monitoring programs are commercial products with some selling for up to $199, however there are several capable free programs available.
PassMark DiskCheckup  is a commercial product but is free for personal use. One of its strong points is the ability to monitor changes in each SMART parameter over time and use this to predict the TEC (Threshold Exceed Condition). That is, the time when the parameter being measured will drop to below the acceptable level. As well as predicting a future failure date DiskCheckup can also alert the user via popup or email when this has actually occurred.
It all sounds very nice but such predictions are quite fuzzy, so they are at best a guide. Also, predictions can only be made if a trend is measured. Most drives have no such orderly trend. That’s why DiskCheckup almost always indicates "N.A" for the TEC. Besides, to measure a trend the product needs to be always running and not all users want that.
There is another reservation: it doesn’t recognize USB drives. To my knowledge SMART analysis is not available for USB drives but DiskCheckup doesn’t even recognize your USB drives.
HDD Health  is another utility that is worth looking at. It has the immediate advantage of being pure freeware and it does recognize USB drives, though as noted, it cannot provide SMART analysis for such drives.
It takes a simpler and probably more meaningful approach to predicting drive failure. It doesn’t focus on predicting a failure date, but instead warns you when individual parameters are deteriorating. I quite like it, a case of how sometimes less is more.
There is an Open Source Project called "S.M.A.R.T. Monitoring Tools"  that offers two programs to control and monitor storage systems using SMART. This was originally a Linux project but there is a Windows version. This one is really for sysadmins, not end-users.
A final possibility is HD Tune . Like the other two utilities it reads SMART parameters and gives you a report on your drive health. However it is designed to give a snapshot report rather than act as a monitor. HD Tune does a lot more than report your hard drive health: it also benchmarks your hard drive performance. The way it does this is quite neat. It scans your disk, then reports random access time and data transfer rates across your whole drive; that is from the outermost to innermost cylinders. It will also scan your drive for sector errors and report drive temperature as well. It may not be the slickest hard drive health monitor but it is a very capable general hard disk utility to have in your toolkit.
If you want to continuously monitor your disk drive condition "HDD Health" would be my top recommendation. Many users however, would be happy with spot checks. For that application HD Tune should be considered. It will do the job perfectly well and you’ll get a competent drive benchmarking utility as well.
 http://www.passmark.com/products/diskcheckup.htm Free for personal use, Windows 98-XP, 404KB
 http://www.panterasoft.com/ Freeware, Windows 95-XP, 901KB
 http://www.hdtune.com/ Freeware, Windows 2K-Vista, 626KB
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