Some info disloged from a few years collection. Disk drives follow the classic failure rate curve. Higher initial failure, low failure during the expected service life with failures increasing towards the end of service life and beyond. Expected service life I usually associate with the manufacturer's warranty time, typically 1, 3 and 5 years for some. MTBF is a calculated time based on many factors. A manufacturer may look at the history of platter failures, head failures, head positioning failures, motor failures, electronics failures and derive an MTBF. An MTBF of 10 years is hard to prove when a drive is designed, built and on the market in a year or less. So warranty life plus X-time is a good guide for service life although the majority of a particular disk would last beyond warranty time. How a disk is used and its environment will impact service life. Is it on a desk top PC or on a laptop in a rolling boat in salt water. Do we turn the disks off gets into start/stop cycles. Again a manufacturer provides a spec on start/stop cycles. I just had a disk fail this year after continuous use for 10 years, aside from moving time to other locations. It began with a reluctance to spin up (stiction) and a good twist of the decktop in the rotational plane of the disk would get it going. Then I had to take the HD out and twist it to get over stiction. Then it died. The little and big drives in the systems where I worked were never turned off, error rates could be increased by temp changes. When a disk spins down, the read/write heads retract to a landing zone or to a safe zone depending on design. You can hear this in some disks as the heads are pulled back before the disk motor power is turned off. A typical minimum start/stop cycle spec for a laptop drive might range up to 600,000 and beyond for higher quality HD's when using IBM load/unload technology. Laptop disc specs are often higher than desktop because it is expected to turn off the drive more often to conserve battery power. The load/unload feature has a ramp that lifts the heads to park them rather than use a landing zone on the platter. A reality check: even at 200 times a day it is still less than the spec during the service life for a quality drive. So if we take a laptop used on a boat for navigation, it is very unlikely you would reach the start/stop cycle spec unless you spend a ton of time navigating, like day and night for years. A factor to consider in start/stop cycles is the operating temperatures of the unit. It heats and cools every time it changes state. A very warm drive that is left to cool in a humid environment can draw in nasty air. The temp swings may have a bigger effect on the electronics in the disk than the actual start/stops. Shock shortens the life of course. The platters in notebooks are usually 2.5 inches and smaller and have little mass to be affected by rolling. Flying from wave to wave where you get pounding could exceed the g rating of the drive. Mount the laptop on a board on a foam block if you do white water trawlering. Thus a disk may die from things other than load/unload. Drives are cheap. One can get a spare, install it in the laptop, do a restore from the Windows CD's, install the nav software and charts. During use of the original drive in navigating, backup routing etc data to the USB stick, often can be done automatically. Now if a drive craps out, pop in the new ready to roll disk and carry on. You don't need lots of gigs for a backup disk. I don't think I can wear out a disk before the rest of the laptop has a problem. Like I spill a "liquid" in the keyboard. I drop it. Spray from the open door by the helm gets into it and freezes because it is 20 degrees. It is like the eye doctor- which is better, A or B. Two engines or one, sorry could not resist. Maine Doug Happy Thanksgiving. Call a friend or relative. Hug the kids. No whining till Monday