need a HDD

<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: &lt;jpero(a)sympatico.ca&gt; To: &lt;classiccmp(a)classiccmp.org&gt; Sent: Tuesday, December 12, 2000 1:13 PM Subject: Re: need a HDD that the me