Manafacture: Lenovo File size: 100.44 kb File name: Language of manual:

Free link for this manual available at the bottom of the page

Head unloading for increased hard disk drive shock tolerance
As a result of extensive testing with the computer lid both open and closed, IBM
has found that in typical drop accidents either from the knee or a desk to a
concrete floor, the internal hard disk drive is protected by the durable ThinkPad
shell so that the received shock level to the hard disk drive generally does not
exceed 800G or 800 times the force of gravity. Since 800G is the maximum rating of
shock tolerance of the hard disk drive with the head unloaded, the hard disk drive
can be better protected during most of these common accidents in typical usage if
the disk head is unloaded prior to receiving the shock impact. Head unloading can
take 300 to 500ms, and the average duration after detecting a free-fall situation is
300ms. Therefore, it is too late to start head unloading after detecting the free-fall
situation. This makes it necessary to concentrate on the behavior of the machine
prior to a drop. The initial behavior acts as a prediction of the impending accident.
In general, the duration of the predicting event is much longer than the actual
free-fall. This enables the active protection system to respond to the impending
accident prior to receiving the shock. The machine posture or system orientation is
constantly checked by monitoring acceleration and using a prediction algorithm to
statistically analyze recent behavior in typical usage. Head unloading is initiated
by degrees of tilt, acceleration, or shock. The degrees at which head unloading
occurs are adjusted and fine-tuned every time a proper prediction is applied for
the current motion. The disk drive head remains unloaded until detecting a stable
environment for approximately one to four seconds depending upon the amount of
excessive acceleration at the beginning of the current shock or posture change.
Use of Prediction Algorithm
The active protection system employs a heuristic learning algorithm to track
system orientation. The Shock Manager, a system thread created by the
Shockprf.sys of a kernel mode device driver, analyzes the variations in acceleration
and collects system orientation data into the Shock History Database. The collected
data is then used to tune sensitivity and predict excessive shocks. This tuning is
important in minimizing the disk performance penalty caused by prediction
failures. Once the Shock Manager detects a certain variation which may be
equivalent to one usually seen just before receiving an excessive shock, the Shock
Manager acts immediately to stop the hard disk drive.
The sensitivity to predict a shock varies depending on usage conditions. In general,
the more stable the ThinkPad computer stays, the more sensitively the Shock
Manager behaves. The Shock Manager focuses its attention on the current
acceleration variation and the weighted average in the recent past. The log is used
to minimize intrusive operation during normal usage of the computer. If the hard
disk drive head is unloaded after detecting a potentially harmful situation, the user
can shorten the current head-unloading period up to 1 second on the condition
that a calm state, stable enough to remove the risk of a drop, continues for at least
one second and at the same time mouse movement activity for more than 200ms is
detected thereby informing the active protection system that this is not a drop
situation.
The design of the active protection system allows for certain shocks or vibrations
that fall within a span of accepted or normal motion and does not repeatedly stop
the hard drive when this level of motion is detected. You can select a checkbox in
the properties window to temporarily disable hard drive protection while
repetitive motion or vibration is detected. This feature is particularly useful when
2
IBM Active Protection System Whitepaper

---

...

Other models in this manual:
Notebooks and Netbooks - R50p Laptop (ThinkPad) (100.44 kb)
Notebooks and Netbooks - T41 Laptop (ThinkPad) (100.44 kb)
Notebooks and Netbooks - T41p Laptop (ThinkPad) (100.44 kb)

Download now

Please, enter two numbers from picture: