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

[Johnny Billquist]

On 2016-02-14 23:54, William Pechter wrote:
> In article <n9ps0p$fue$1 at Iltempo.Update.UU.SE>,
> Johnny Billquist  <bqt at softjar.se> wrote:
>> 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
>> pdp is alive!                     ||  tryin' to stay hip" - B. Idol

Let's start by pointing out that the story do not say RP06. That's just 
my guess on a possible drive it could have been based on the fact that 
it at least have several phases in the feed. Capacity wise, it's larger 
than the story's drive. But timewise is also strange, as early 90s RP06s 
were on the way out, if they weren't gone already. It's not something I 
would expect to see anymore, except sites which had some pretty old 
stuff around.

> Actually I've seen RP04's spin backwards banging their brushes (which were
> ECO's out on service contract sites)against the stops... Happened
> at New Jersey Bell Telephone when they electricians didn't check the phases
> sent to the three phase RP04s.  RP05's and RP06s only used two phases.

I know I've played with RP04s, but I can't remember exactly how the 
power setup was inside them at the moment.

> This was in New Brunswick New Jersey around 1984-85 or so.
>
> This was when the Telco's were buying up used and surplus pdp11's for
> internal use as line maintenance macines...for SCAMOS etc -- before they
> moved to Vax systems and AT&T 3B boxes.
>
> This was just when DEC was discontinuing the 11/70's due to FCC RF noise
> spec issues.
>
> I guess they never figured on checking the phase to phase before we tried to
> power up the drive.  All drives immediately blinked and went unsafe doing a
> full head against stop retract due to the packs spinning backwards.

Yikes.

> IIRC the Sperry/Itel RP04's were completely three phases where the RP06's used
> two for the drive and 1 for the DCL (IIRC).  Could've been just two with
> the DCL and one drive motor set up on the same phase and the second DCL
> and the first one's drive motor on the other when they were connected together
> sharing the power.

Looking at manuals, the DCL appears to be hooked to two phases.

> It could have been that there were old RP04's on the site when a PDP11 was
> replaced by a VAX... The RP07, IIRC was also a three phase drive with a
> semi-sealed HDA.  If those 400+mb platters blew out... boom.

The RP07 is a very different drive. I found it pretty cool. But I would 
have to go a dig through more memories to talk about it. But that drive 
is unlikely to have been the drive of the story. 506MB by the way, if my 
memory serves me.

> The RP06's were more than 85 lbs.  The platters weren't.  Perhaps the HDA
> on the RP07 was about 85 lbs.

The whole drive, for all RP drives, are definitely more than 85 lbs, 
yes. Had to repair the spindle motor of an RP07 once, but I can't 
remember ever taking the HDA out, so I don't know how much it might have 
weighted.

> RA drives weren't three phase.

Indeed not.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol