S.M.A.R.T : What's the difference between "Start/Stop cycle count" and "Load/Unload cycle count"?

Q1. What is the difference between "Start/Stop cycle count" and "Load/Unload cycle count" ? Q2. What happen to the hard-disk when a computer is put to sleep mode, does the spindle moter stops spinning and rw heads are automatically parked to the landing zone ?

Thanks

The Start/Stop Cycle Count is the amount of times the hard disk spindle has started to spin, and stopped spinning. This spindle will power up and start spinning happen whenever the drive is turned on or resumed from sleep.

The Load/Unload Cycle Count is how often the actuator arm is parked in the loading zone. The actuator arm holds the head which reads/writes to the disk.

For a diagram (I doubt you need it, but if so) check out: http://en.wikipedia.org/wiki/File:Hard_drive-en.svg

What is the difference between spinning up and parking the read/write? Simply put, your hard disks might be spinning, but if nothing has been written/read for a while, it might park the head, but not stop the hard disk spinning. Hard drives will always park the heads before powering down, unless power is abruptly cut off.

On your computer you can specify when shut down power to the hard disks (In Windows, go to Advanced Power Optins and check out "Turn off hard disk after x minutes") after a certain period of inactivity. This is something your operating system decides.

The head parking behaviour is not usually controlled by your operating system. It is controlled by the disk drive itself. Each disk has it's own method of choosing when to park the arm. For example, a notebook drive might be a lot more aggressive in it's arm parking because it designed for a portable computer which might be jolted around a bit. An enterprise server drive, on the other hand, doesn't expect to be moved around as much (if at all!) and will also be expected to have the fastest possible access, so it won't park the arm as much.

There are some tools you can use to change the head parking behaviour. Hard drive vendors often release such utilities - have a look at their websites if you want. There are other, more generic tools, such as hpadm for the Mac, but I'd always advise using your HDD vendors tools first. These tools communicate directly to the hard-disk firmware and modify the settings on the hard disk level, so moving that hard-disk to another computer will retain those settings.

To answer your second question, Yes, when you put your computer in to sleep mode, the hard-drive will first park it's read/write head and then it will power down the HDD spindle.