[Info-vax] OT: the Daily WTF for today is a VAX/VMS story

[Johnny Billquist]

On 2016-02-14 10:48, already5chosen at yahoo.com wrote:
> On Wednesday, February 10, 2016 at 10:03:18 PM UTC+2, rdpi... at gmail.com wrote:
>> See
>>
>> http://thedailywtf.com/articles/overpowered
>>
>> for a nostalgic trip down memory lane.
>>
>> RDP
>
> There is one technical detail that I didn't understand: how did hard drives get their three-phase AC power when operating from battery ?
>
> Also something sounds wrong with rpm. 3000 rpm is a correct AC frequency in the most of the world, but this particular story happened in USA, right? Isn't it 3600 rpm there?
>
> More I think about it, more the story of VAX hard drive with three-phase AC motor (in early 90s, non-the-less) appears apocryphal.

The story was fun, but it is indeed not based on facts.
Yes, there are drives that run from 3-phase power, such as the RP06, 
which could have been a base for the story.

However, no hard drive uses a 3-phase AC motor to drive the disk. Anyone 
with half a brain should realize this. 3 phase AC motors always follows 
the phases of the supply like slaves. There is no spinup time. You go 
from standstill to full speed immediately, always. That is not how you 
want to spin up a disk drive.

The RP06 uses two phases actually, but it does it to extract more power. 
The actual motor is still a DC thing. And yes, it spins at 3000 rpm (I 
think that is correct) both in 50 Hz and 60 Hz countries.

I do not know for sure how they dealt with battery backup for such 
drives. Maybe someone else can tell?

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
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