Re: Apple II Disk Drive Question

["Bill Garber" <willy46pa@comcast.net>]

"David Empson" <dempson@actrix.gen.nz> wrote in message 
1hc6nim.1rfsb061a1gyclN%dempson@actrix.gen.nz">news:1hc6nim.1rfsb061a1gyclN%dempson@actrix.gen.nz...
> Don Bruder <dakidd@sonic.net> wrote:
>
>> In article <1hc5pp1.ked6xj1br0avnN%dempson@actrix.gen.nz>,
>>  dempson@actrix.gen.nz (David Empson) wrote:
>>
>> > There is a bit on page 9-45 (with reference to the ProDOS driver) which
>> > says that the maximum variation due to rotation speed and disk flutter
>> > must be less than plus or minus 4.7%.  This translates to about 2.3%
>>
>> There's no nicer way to put this, and I've seen you making the exact
>> same *JUST PLAIN WRONG* statement multiple times now, so I'll just be
>> blunt:
>
> I beg your pardon? That is the first time I've even READ that section of
> the book in question, let alone referenced it, so I don't know how I
> could have made the statment "multiple times" (apart from in a single
> post, which was derived from the same value).
>
>> It doesn't "translate" to anything, period. "+/-4.7%" explicitly states
>> that 4.7% below OR above 300 RPM is acceptable - no translation required
>> - There's an explicit 9.4% window, with the target speed of 300RPM
>> centered in it.
>
> Quote from the book:
>
> ... the 30-cycle period between reads means that there can be no more
> than 3 parts in 32 variation in speed between the reading and writing
> drives. In other words, drive speed variation plus speed variation due
> to disk flutter must be less than plus or minus 4.7% or occasional
> reading errors will ocucur at the bottom/middle border in a data field.
>
> [end quote]
>
> 3/32 = 0.09375.  Therefore you are correct, it is a +/-4.7% variation
> from 300 rpm, so my figures were incorrect, and the actual limit on the
> range of rotation is speeds is about twice what I said, about 286 to 313
> rpm should be OK.
>
>> It does not say anything about 2.3% - If that were the intent, there
>> would be no "+/-" involved - it would be a straight "4.7% variation".
>
> The paragraph in question was talking about variation in speed between
> reading and writing drives, and I interpreted the quoted 4.7% figure as
> being the allowed variation in speeds between read and write drives,
> rather than the allowed variation from the midpoint.  I didn't notice
> that the 3/32 ratio was twice that.
>
>> 4.7% of 300 is 14.7. Therefore, 300-14.7 = 285.3, and 300+14.7 = 314.7,
>> meaning any speed from 285.3 to 314.7RPM is within specs.
>>
>> Your incorrect interpretation of what's spelled out explicitly in black
>> and white narrows that range considerably - 2.35% of 300 = 7.05, making
>> minimum RPM under your interpretation 292.95, and maximum 307.05.
>> Yes, it's a tighter tolerance. But it's not the tolerance specified.
>>
>> I know that's nit-picking, but if you're going to throw math around, at
>> least get it right, huh?
>
> If you are going to post to Usenet, at least have a modicum of courtesy.
> I made a simple mistake, there is no need to be rude about it.


What a relief. I thought I was the only one he
was rude to.  :o)

Bill Garber