# Re: "Dangerously dedicated" yet again (was: cvs commit: src/sys/kern subr_diskmbr.c)

```+-------[ David W. Chapman Jr. ]----------------------
| > > :> > IBM DTLA drives are known to rotate fast enough near the spindle
| > > :> > that the sustained write speed exceeds the ability of the controller
| > > :> > electronics to keep up, and results in crap being written to disk.
| >
| >
| > I would adssume it actually the tracks FURTHEREST from the spindle..
|
|
| Wouldn't the linear speed be faster closer to the spindle at 7200 RPM
| than at the edge?```
```
er no.

The circumference of a circle is 2 PI r.

So as your distance from the spindle increases the amount of physical real estate
you're traversing increases. Since you are turning at a constant angular velocity,
your linear velocity increases as the distance from the spindle increases
by a factor of PI (or around 3 if you're not a maths person).

Even been at one of those carnivals where they have a spinning thing?
It's easier to stay near the centre, than near the edges, because you are moving
a *lot* quicker at the edges.

And just for the hell of it;

If you have a 3 unit disc doing 1 RPM

If you're 1/2 unit out you're doing  ~3 units/sec
If you're one unit out, you're doing ~6 units/sec
If you're two units out you're doing ~12 units/sec
at three;                            ~18 units/sec

Multiply by 7200 and s/units/inches/
The outside of your disk is really moving

The density of the sectors at the outer edge is lighter than
near the centre, which mitigates the speed some what.

See Also: artficial gravity in space stations/ships/objects

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```