need a HDD

From: Don Maslin <donm_at_cts.com>
Date: Tue Dec 12 23:39:25 2000

Jeez! Four times!!!
                                                 - don

On Tue, 12 Dec 2000, Richard Erlacher wrote:

> <stroking beard and clearing throat>
>
> It seems as though, whenever there's a substantial discussion about rotating
> memory systems for the computers of yesteryear, the muddled distinctions
> between "drive type" as used for describing what is being sought gets mixed
> up with "drive interface" and "modulation type" among other concepts. Here,
> again, we have a reference to MFM/RLL, both of which are modulation
> techniques, both of which were commonly used by SCSI, SMD, and ESDI drives,
> among others. Another item that doesn't seem to help, is that the
> distiction between physical interface, e.g. ST-506/412 (actually the same,
> from all obvious features, though there were some minor differences), gets
> mixed in as well. SMD is an interface specification, as are SCSI, SASI, and
> ESDI.
>
> A look at the SEAGATE spec's for their various drives, including those made
> by CDC before SEAGATE acquired them, and you'll see ESDI drives that use RLL
> and other that use ERLL and still others using MFM. Likewise with SCSI
> products and SMD.
>
> Real confusion comes from the fact that people referred to drives as being
> RLL or MFM drives, which was, perhaps, a difference, but not in the drives.
> There were a few models that performed badly with RLL that performed better
> (more reliably) with MFM, but those were the exception rather than the rule.
> The drive, actually the head/media combination, determined the flux reversal
> density, and the spindle speed determined the resulting bit rate, right? It
> seems simple enough. Sadly, there's more ... particularly after the
> adoption of ZBR, in which the data rate with respect to time borrowed from
> the strategy of CLV recording as used with optical media as opposed to the
> previously popular CAV. It's no wonder that folks are confused, but it's
> been 10 years or more since MFM fell out of fashion, and, in fact, since
> controllers became a drive function rather than a host adapter function.
> You'd think folks would have gotten these concepts straightened out. <sigh>
>
> <getting down from soapbox>
>
> That drive I'm looking for has to have at least 8 heads, and it has to have
> at least 640 cylinders. In this particular case, until I find my source
> code, I can't benefit from more heads or cylinders, nor can I "get by" with
> fewer. I have plenty of drives that don't fit this model, but I want one
> that will, to help stomp out an immediate fire.
>
> Knocking out an interface that would handle all the modulation schemes, data
> rate variations, and wiredo data rates, etc, might not be so easy as it
> looks. Yes, one could analyze the format with a combination of various
> hardware and firmware techniques, and that way one could continue to use
> hardware that would otherwise be unsupportable, but that's the sort of thing
> that companies like Adaptec or Mylex spend megabucks to accomplish for just
> ONE of the modulation types. The reason that's what's spent is because it
> can't really be done for much less. If you want to do that, then have at
> it.
>
> I've done lots of this sort of work, yet nobody's offered me a dime to build
> an RLL or MFM controller for an ST506-type drive in the last ten years.
> It's much easier to replace the drive with one of the more modern ones,
> rated, yet not really expected, to have a lifetime of >100K hours, while the
> ones of 10 years ago were rated for MTBF's of 5-10 KHours. I can't see how
> anybody could justify the investment in technology that will croak in a year
> or two. It's easier to rework the firmware and replace the old, 150-lb SMD
> with a 150-gram microdrive of 20x the capacity. You can mount that on the
> board next to one of the IC's and it will get lost.
>
> Thanks,
>
> Dick
> ----- Original Message -----
> From: <jpero_at_sympatico.ca>
> To: <classiccmp_at_classiccmp.org>
> Sent: Tuesday, December 12, 2000 1:13 PM
> Subject: Re: need a HDD
>
>
> > > Date: Tue, 12 Dec 2000 16:33:06 -0800
> > > From: Marvin <marvin_at_rain.org>
> > > To: classiccmp_at_classiccmp.org
> > > Subject: Re: need a HDD
> > > Reply-to: classiccmp_at_classiccmp.org
> >
> > >
> > >
> > > Richard Erlacher wrote:
> > > >
> > > > Just in case someone's got one, I'm looking for a hard disk with 640
> > > > cylinders x 8 heads to replace a Rodime 204E. If anyone has somthing
> that
> > > > will fit this geometry, and it's available, I'd like to be informed.
> > >
> > > My memory (and docs) are not so good right now, but isn't that basically
> the
> > > same configuration as the Seagate 251? If so, I probably have several of
> > > them just sitting around *waiting* for an application to pop up :). Let
> me
> > > know if you need one.
> >
> > Mavin,
> >
> > In MFM world, most commonest n of heads and cylinders is usually 6xx
> > and 8xx and 4 to 6 heads. Beyond that, that not very common.
> >
> > ST251 is 820 (check) x 6 heads (not met) needs 8.
> >
> > On this topic,
> >
> > Even I was latecomer to MFM I deal with MFM/RLL, exrotic ESDI in
> > early '90's.
> >
> > While I was thinking, why not have someone design and program a
> > adapter to take MFM/RLL as well as ESDI and translate it to SCSI or
> > IDE and wrap it up in DSP and all in one microcontroller, interface
> > chipset and some ram, rom? This way, helps people to upkeep their
> > oddball machine that insists on odd drives. To set up that adapter
> > board to report specific cylinders range and heads, N of sectors that
> > reports back to that host machine and just "LL format" the scsi or
> > IDE hd if needed then HLF it in normal manner as you would do with
> > any MFM/RLL, ESDI drives.
> >
> > Cheers,
> >
> > Wizard
> >
> >
>
>
>
Received on Tue Dec 12 2000 - 23:39:25 GMT