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From: pnl@hpfinote.HP.COM (Peter Lim)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Perstor controller?
Message-ID: <19450073@hpfinote.HP.COM>
Date: 28 Jun 90 20:36:19 GMT
References: <780023@hpsad.HP.COM>
Organization: Hewlett Packard CICD
Lines: 44

From patf@.HP.COM (pat fung) /  4:04 pm  Jun 26, 1990 /, Pat Fung writes:

>   This is how you get 140% more capacity using RLL 2,7 encoding. RLL 2,7 uses
> 7 bits to encode 5 data bits with no less than two consecutive bits of the
> same type. The worst case of flux change is every two bits compared with MFM,
> the worst case is a flux change every bit when alternating 1's and 0's are
> encountered. So in the space of 7 bit of MFM recording, you get 14 bits of
> RLL recording using the same flux density. But the 14 bits of RLL data 
> is only
> representing 10 bits of actual data. The increase in capacity is:
> 
>                       10/7 = 1.42 or 142%
> 
>   By playing with the inter-sector gap, 26 sectors can be squeezed into a
> track compare with 17 sectors with MFM. The capacity boost is more like
> 25/17=1.52 or 152%.
> 
This is the most convincing argument I heard on this topic. So, this means
that the info I read about from this Brady book is bullshit  :-).
... and I stand corrected.


I also need to apologize to the net for posting unverified info.
I did claim that Perstor has 1:1 controller; but I checked this out to be
not true.

The absolute truth is that:

Perstor produces 8-bit and 16-bit controllers; and at least one of the
two comes with a miserable 2K-byte on board buffer. This means that if you
have a very fast computer, it is theoretically possible to run Perstor's
controller at 1:1 interleave. But the catch is ---- so far, such computer
doesn't exist.

Cheers.


Regards,                       ## Life is fast enough as it is ........
Peter Lim.                     ## .... DON'T PUSH IT !!          >>>-------,
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