why won't your new hard drive last as long as your old hard drive

Western Digital wd40 bad clusters Western Digital WD400

Born: December 2003.
Died: February 2009.

Life: Just over 5 years

Western Digital wd40 bad clusters Western Digital WD200

Born: November 2001.
Died: May 2009.

Life: Just over 7 years

Statistical probabilities and samplings aside, it's a safe bet to state that your new hard drive won't last as long as your old hard drive.  This assumes your old hard drive is from your typical 4 to 8 year old pc.

The reasons are simple.

Your 7 year old hard drive will be the unbiquitious 20 to 40 gig size, in a 3.5 inch desktop form factor. Comparing to 2009, the smallest drive available locally is a Western Digital, Hitachi, Seagate, or Excelstor hard drive weighing in at 160 gigabytes. In the 7 years which have passed (comparing a Western Digital WD160 with a WD400, engineering feats in the ability to pack more information into a single hard drive disk platter has resulting in packing more information per platter today, than say 6-7 years ago. With the price point so slow with hard drives, the customer will be interested in buying a larger drive yet - the old PATA (parallel ATA) hard drives can be found in capacities of 250, 320, up to 500 gigabytes. Pickup your old 40 gig hard drive, then pick up a new 500 Gig PATA hard drive, you'll notice the 500 gig hard drive has gained considerable weight.

Western Digital 500 gig Sata Western Digital 500 Gig World Edition Hard Drive

Born: March 2007.
Died: May 2008.

Life: 13 months

Western Digital 500 gig Sata Western Digital 160 Gig Sata "High Reliability" Hard Drive in Dell Optiplex, click of death. Two of the same drives in the office (2 other Dell Optiplex PC's purchased at the same time) are working properly.

Born: February 2008.
Died: December 2009.

Life: 22 months

Recovery Job Cost: $2,430 (user did not make backups)

More storage density requires more disk platters and more actuating heads, which contributes to more stuff which can wrong. Mechanical tolerances becomes extremely critical because so much data is packed onto the platter - this is called "high areal density." More storage density results in hotter operation (again more disk heads, more platters, bigger motors, more friction). Running any electronics hotter causes reduced service life, however evidence from a google study from 2007 suggests running a drive too cool can reduce its service life*.  

You may be inclined to think your first two years of hard drive service may be "peace of mind."  You may be sadly disappointed - regardless if you buy a new computer or replace the hard drive in the old computer.

Now more than ever you should backup, because the life of a high capacity, high density hard drive is uncertain. New technologies, including PMR (Perpendicular Magnetic Recording) increase the likelihood of failure. I base this on simple physics. Anytime you pack more information per square inch on a disk surface, and you add more platters and more drive heads, you increase the likelihood of eminent disk failure.

*Study finds hard drive failure rates much higher than makers estimate.

Common causes of Hard Disk Drive Failure, by Ontrack Systems.

Article quote: "Today's hard drives have no room for errors when it comes to platter and head alignment. The tolerances are so exacting that hard drive manufacturers even design ways to keep the Base-Casting Assembly, where all the components are attached to, from shifting due to high temperature situations."

What does it mean when a hard drive has a head crash?  From howstuffworks.com.

Comparing Logitudinal and Perpendicular Magnetic Recording. The superparamagnetic effect soon will prevent hard drive manufacturers from continuing to shrink the magnetic grains that make up data bits.

Big Hard Drives = Big Failure Rates? How Safe Is Your Data?  A blog from a Jeff Beard.

Minimizing Data Loss with Hard Drives - Tips  Some common sense tips, plus some tips you may not know.

Disk failures in the real world: What does an MTTF of 1,000,000 hours mean to you?  A study by Carnegie Mellon University, a bit of a technical read.