Re: [vcf-midatlantic] Hard drive art
Thank you for your thoughtful comments, I'm very sorry if I caused any agitation as a result of my art. I must admit, lurker may have been too strong of a word. I have a friend involved with vintage computers and is the one who pointed out the one 14" platter I found from this group. Since then I subscribed, but dont get a chance to read often. The majority of my art supplies have come from Ebay with a substantial investment on my part, most being sold as scrap. Some platters, spacers, and actuators were bought disassembled already. The ones not sold as scrap, I'm paying the value of a working drive. Now at this point anyone else could have purchased these drives and attempted to use them. I would be happy to work with people from this forum to sell some individual parts one might want. As for the drives themselves, I've spent over $300 in shipping alone for some of the 8" and 9" drives I've bought and disassembled from CA. I've been scanning Ebay for over a year targeting value, and specific models , I've got 60+ searches I check daily. I've invested thousands of dollars, countless hours disassembling drives, countless hours designing and creating my art, and tons of blood and sweat. That all being said, I do have an impressive collection of hard drive parts from the last 50 years, and I can understand your frustration as a vintage computer restorer. I would honestly rather use my parts for art, but I could be willing to help provide parts for sale where I could. I have sold 90% of the circuit boards on Ebay, including many from real vintage drives. I will say, when I looked into starting this project, I did tons of research into art made from hard drives, what I found was there were lots of clocks, and a few sculptures here and there, but nothing anywhere near what I had in mind to make. So, I found something new and unique and creative to reuse many old hard drives that eventually all would find their way to a scrap yard or landfill. New + unique + recycling seems a rare thing these days, and something I feel the world needs more of. I think the shelf life (or wall in my case), can out live any working vintage hard drive. That being said, I'm happy to work with those who want to prolong their own vintage computers. On Sat, Apr 13, 2019, 12:43 PM Herb Johnson via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
Brian Brubaker posts about use of hard-drive parts to create art, for our appreciation. Well, this use of vintage electronics as art, gives me pause. I thought about it; I wrote a lecture; I decided a lecture would not be read or appreciated. So here's my straightforward considerations.
Brian: I restore vintage computers to operation. So I see in parts of your art, computers that can't be restored because they were demolished. That's not an abstraction, for me - that is a fact.
This situation is not your fault. However, you have posted in a group of vintage-computer restorers; so my point is relevant in this forum.
So: Brian, I encourage you to make available, such ancient drives and parts as might be useful to restore ancient computers. I'm sure you can get guidance about doing so.
I don't mean to spoil your fun or interests. Do not go back to "lurking" because some old-guy doesn't like your work - that is not what I said, that's not how I said it. Art evokes responses; the artist can't determine all those responses. This is part of my response. And certainly, there's art today which is FAR more controversial than a bunch of old computer parts. I'm making a point, not cursing your works, which have artistic merit.
Brian, thanks for showing your works in this forum.
Herb Johnson
-- Herbert R. Johnson, New Jersey in the USA http://www.retrotechnology.com OR .net
All good responses, Brian, you've thoughtfully described your process and activities. If my judgement matters, you're doing some of the right sort of stuff within the vintage ecosystem. As you state, you have some purposes and intentions that are certainly of value; and you produce items which are a product of your considerations and efforts and investment. I did not suggest your art lacked consideration, value or merit. But you also compete for use of those drives you buy whole - "could have purchased" suggests that. You mention such use as "those who want to prolong their own vintage computers". Well, that's a limited view. So this discussion is not about "agitation", yours or mine. This is a mutual learning conversation, in principle why people post in forums. I can tell you as a fact, not all of those whole-drives go to the landfill or become recycled. Several of my colleagues recently engaged in buying 8-inch hard drives, to restore Intel brand Multibus (call them "industrial") vintage computers. They were doing component level repair, and reverse engineering of their software and hardware. Whole drives, even not completely working, allow them to do this. And of course they hoped for working "HDAs" (hard disk assemblies, the working platters and heads) not only for repair, but to *recover original software* not otherwise available. Some go to great lengths to extract operating information about vintage computers; they make it available, often freely, to others. I've offered S-100 manuals for DECADES. That's not about "prolonging my own vintage computer". And, just as you suggest your art has an extended lifetime; so does purposeful recovery and restoration of vintage computers. Lessons learned and software and hardware recovered, as I've described, is and will be used to restore additional computers of the same kind. The effort is itself a demonstration of restoration possible for other computers. That encourages others who otherwise would give up such an effort. You can visit my Web site, to see many restoration examples. People tell me, they learned from my "art", and went on to other kinds of vintage computing, or modern "versions" of vintage computers. The contents on some computer drives may happen to include data of personal value. Some start with wanting to "restore their own computer", or their first computer, or their parent's computer. But people who are *persistently* involved in vintage computer restoration restoration, recovery (or expansion) of *technology* is often their primary value. Most of that work is done by individuals or collectives, not (in my experience) by institutions. Few have a large budget; you mentioned yours; budgets vary. Also: I have clients who use vintage computers for purpose; they lack my technical skills, or resources. They need drives for continued operation. Some purposes are industrial, unique control equipment hard to replace. Other clients, well, they are satisfied with their vintage software, which won't run on modern hardware; or runs poorly. Modern alternatives have needless complexity, or excessive cost. Who am I to tell them they are "prolonging"? Or to pass judgements on their personal interests? Pardon me, or them, for being old and continuing use of a known tool! There was a time, when computers were not disposable consumables, and software worked adequately. That's another kind of "preservation", that point of view. So, you have some feedback from me, representing the "other side" who have continued purpose, of value, some beyond personal; for these drives, those "personal computers". We have things in common, we both have our reasons, but we are in some competition. I'm glad you give "us" some consideration. If I determine some of my drives no longer serve any purpose, I'll consider offering them to you as opposed to scrap. And I'll see if you have some boards I may use for repairs. Thanks for the discussion and the exchange of considerations. Herb Johnson On 4/15/2019 7:50 PM, Brian Brubaker wrote:
Thank you for your thoughtful comments, I'm very sorry if I caused any agitation as a result of my art.... -- Herbert R. Johnson, New Jersey in the USA http://www.retrotechnology.com OR .net preserve, recover, restore 1970's computing email: hjohnson AT retrotechnology DOT com or try later herbjohnson AT retrotechnology DOT info
"not all of those whole-drives go to the landfill or become recycled" I would argue that you may have a limited view as well, and while I may not have a complete picture of what vintage hard drives are currently used for, I believe my point is still valid. For all the points you mentioned, EVERY hard drive eventually stops working and is thrown away or recycled(aside from the 1% that go to museums). Furthermore, I would suggest that hard drives with moving parts will soon no longer be produced or used. I'm no futurist, but I'd bet they are mostly gone within 20 - 30 years. I would ask you how long you honestly think people will be attempting to use these drives from the 60s-80s? I expect my art to last lifetimes, can you say the same for any vintage computer today? you referred to yourself as the "old-guy", I'm not exactly in my 20s either. I'm a programmer by nature, and have a love of hard drives that has existed most all of my life. With that being said I have had my fair share of drives die, data lost, and attempts to transfer old data from older storage devices so I certainly understand your point of view. Now, at this point I've already disassembled most every hard drive I've bought, including 36 8"-10" drives, 179 5.25" drives, and about 54 3.5" vintage drives. Over 200 different models. The only things I've not yet fully disassembled are from 1" and 2.5" drives, I imagine these don't qualify as vintage. I've sold 90% of the circuit boards, 95% of the scrap aluminum and other outer casing materials. At this point I've invested about as much as I can into my art supplies, so I more then likely won't be buying many more vintage drives unless I start recouping my investment into my hobby turned side business. What I don't use in my art I sell on e-bay or recycle. I'm more then happy to sell the things I sell to anyone reading this. I have a collection of parts I've yet to list, and some I could be convinced to sell for the right price.. Aside from my art, everything I've sold on e-bay has sold for under it's value, so I'm not exactly trying to get every penny I can, I just can't loose $. I would love more avenues to get old drives, they get harder to find every day. Doing some On Mon, Apr 15, 2019 at 11:30 PM Herb Johnson <hjohnson@retrotechnology.info> wrote:
All good responses, Brian, you've thoughtfully described your process and activities. If my judgement matters, you're doing some of the right sort of stuff within the vintage ecosystem. As you state, you have some purposes and intentions that are certainly of value; and you produce items which are a product of your considerations and efforts and investment. I did not suggest your art lacked consideration, value or merit.
But you also compete for use of those drives you buy whole - "could have purchased" suggests that. You mention such use as "those who want to prolong their own vintage computers". Well, that's a limited view. So this discussion is not about "agitation", yours or mine. This is a mutual learning conversation, in principle why people post in forums.
I can tell you as a fact, not all of those whole-drives go to the landfill or become recycled. Several of my colleagues recently engaged in buying 8-inch hard drives, to restore Intel brand Multibus (call them "industrial") vintage computers. They were doing component level repair, and reverse engineering of their software and hardware. Whole drives, even not completely working, allow them to do this. And of course they hoped for working "HDAs" (hard disk assemblies, the working platters and heads) not only for repair, but to *recover original software* not otherwise available.
Some go to great lengths to extract operating information about vintage computers; they make it available, often freely, to others. I've offered S-100 manuals for DECADES. That's not about "prolonging my own vintage computer".
And, just as you suggest your art has an extended lifetime; so does purposeful recovery and restoration of vintage computers. Lessons learned and software and hardware recovered, as I've described, is and will be used to restore additional computers of the same kind. The effort is itself a demonstration of restoration possible for other computers. That encourages others who otherwise would give up such an effort. You can visit my Web site, to see many restoration examples. People tell me, they learned from my "art", and went on to other kinds of vintage computing, or modern "versions" of vintage computers.
The contents on some computer drives may happen to include data of personal value. Some start with wanting to "restore their own computer", or their first computer, or their parent's computer. But people who are *persistently* involved in vintage computer restoration restoration, recovery (or expansion) of *technology* is often their primary value. Most of that work is done by individuals or collectives, not (in my experience) by institutions. Few have a large budget; you mentioned yours; budgets vary.
Also: I have clients who use vintage computers for purpose; they lack my technical skills, or resources. They need drives for continued operation. Some purposes are industrial, unique control equipment hard to replace. Other clients, well, they are satisfied with their vintage software, which won't run on modern hardware; or runs poorly. Modern alternatives have needless complexity, or excessive cost. Who am I to tell them they are "prolonging"? Or to pass judgements on their personal interests? Pardon me, or them, for being old and continuing use of a known tool! There was a time, when computers were not disposable consumables, and software worked adequately. That's another kind of "preservation", that point of view.
So, you have some feedback from me, representing the "other side" who have continued purpose, of value, some beyond personal; for these drives, those "personal computers". We have things in common, we both have our reasons, but we are in some competition. I'm glad you give "us" some consideration. If I determine some of my drives no longer serve any purpose, I'll consider offering them to you as opposed to scrap. And I'll see if you have some boards I may use for repairs. Thanks for the discussion and the exchange of considerations.
Herb Johnson
On 4/15/2019 7:50 PM, Brian Brubaker wrote:
Thank you for your thoughtful comments, I'm very sorry if I caused any agitation as a result of my art.... -- Herbert R. Johnson, New Jersey in the USA http://www.retrotechnology.com OR .net preserve, recover, restore 1970's computing email: hjohnson AT retrotechnology DOT com or try later herbjohnson AT retrotechnology DOT info
This is becoming an argument. That's understandable, but that's not my goal. My point of throwing the "old guy" card, is to say some interest in vintage computing is persistent, is beyond keeping one's computer running, but in goals you refer to as "museum". Most museums put a computer on a shelf, don't touch: the work I describe re-engages people with now-working computers. Your work also engages others; I don't question the value of art, or oblige it to be for purpose. This is what engagement looks like. You assert the permanence of your art, versus eventual drive failure. Certainly, all things come to an end; I don't give up, neither do you. As I said: we have some common interests, we compete for some resources. That's fine, we are adults, we can work in concert and good will to further mutual ends. You accommodate restoration interests, as do the recyclers. That's good. (You might tell me, where on eBay you sell electronics, I need a CMI 5619 5.25-inch drive for electronics.) I'll remind you: this is a vintage computing forum. I asserted that point of view in response to your post about your art. You've given mostly reasonable responses, thank you. Other people can review our discussion, see work done, make their own considerations. Those were my goals. Thank you. - Herb On 4/16/2019 11:35 AM, Brian Brubaker wrote:
"not all of those whole-drives go to the landfill or become recycled" I would argue that you may have a limited view as well, and while I may not have a complete picture of what vintage hard drives are currently used for, I believe my point is still valid....
-- Herbert R. Johnson, New Jersey in the USA http://www.retrotechnology.com OR .net preserve, recover, restore 1970's computing email: hjohnson AT retrotechnology DOT com or try later herbjohnson AT retrotechnology DOT info
On Tue, Apr 16, 2019 at 11:35:41AM -0400, Brian Brubaker via vcf-midatlantic wrote:
For all the points you mentioned, EVERY hard drive eventually stops working and is thrown away or recycled(aside from the 1% that go to museums).
I think its when we get to drives that only a limited number are left so we are competing that people in this group have problems. For much of the period there are more drives than the collector market can use. More interesting discussion for me would be what have people heard on techniques for repairing drives. I agree all will stop working. When they are plentiful simple repairs and getting another/parts donor is the easy way but that will only work for so long before needing to develop more advanced fixes. So what have people heard on advanced repairs? Somewhat long winded ramblings from a not quite so old-guy. Assuming that the part of vintage computer collecting that wants to run their machine doesn't peter out I expect that some of my machines will be running when I no longer am. I suspect that will include some of my drives. For my RK05's (~1974 14" removable platter) the only parts I see issues with dealing with failure of are the platters and the heads. The bearings look to be reasonably easy to replace for people with access to reasonable tools unlike newer drives. This page about half way down has an interesting repair of RK05 cartridge. http://rescue1130.blogspot.com/2017/11/resolved-copy-and-burn-of-264x-termin... I suspect that I have ran across this when I was reading some of my cartridges in the past but assumed it was damaged platter when I saw the wobble. I still have them so can check and possibly repair them when I get some more of that spare time. Has anybody heard of the oxide binder breaking down on hard drive platters like it does in some tapes and floppies? The RK05 being non contact will help some in tolerance for minor deterioration. If the media deteriorates this could limit how long drives can be kept running. I also think that with sufficient $ or persistence someone will develop a method to re-coat platters if needed. Since the process should work for multiple drive models this may be able to generate enough volume to be worth someone doing this. I would think doing anything about damaged heads will be harder. I heard from one person trying to restore an early synthesizer that was wanting to have a platter swap done to try to recover data from a ST506 with bad bearings that the commercial data recovery places have started to throw out the tools needed to work on these drives due to low demand. From my understanding these places were really data recovery and not drive repair for long term usage. I gave a MFM drive to one of the list members who was looking for drives to investigate bearing replacement. It has the common noisy bearing problem. What was unusual was the second time he powered it on one of the head positioner bands broke. I had never heard of that failure before.
From looking at it I suspect with modern scanning and laser cutters you could actually make a replacement out of the proper spring steel stock.
For repairs that people can't do themselves will costs reach a point where enough people will be willing to pay for them? If not it will be emulators since the costs for them are more likely to go down. I also make an MFM emulator but for me its a tool and not an end goal. That's why I have put so much effort into reading existing disks. I would like to be able to keep the original drives working and if not make sure the data is captured so at least the computer can be kept working. The next step of this I posted about before will be to use my emulator to rewrite the contents back to the disk so hopefully it is usable again. I want to do something more permanent with the shims first. http://www.pdp8online.com/mfm/head_servo/
Speaking of which, Jason P. is doing a class on hard disk repair at VCF East. :)
Yes, working on drives is going to be a portion of that class. Unfortunately as I've dug into the motors, it looks like servicing them might be very difficult. Another issue we'll run into is servo tracks, and no way to re-create them once they fade. With the software / fixtures only available at the factory I don't know how we could recreate those tools. -J On Tue, Apr 16, 2019 at 11:21 PM Evan Koblentz via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
Speaking of which, Jason P. is doing a class on hard disk repair at VCF East. :)
-- Jason Perkins 313 355 0085
On 4/17/19 11:46 AM, Jason Perkins via vcf-midatlantic wrote:
Another issue we'll run into is servo tracks, and no way to re-create them once they fade. With the software / fixtures only available at the factory I don't know how we could recreate those tools.
First you'd need to first determine the exact format of the servo tracks. Keep in mind that they may not be "digital" tracks. If the format cannot be determined from patent info, etc, then the only choice might be to temporarily disassemble a functioning drive of the same model, identify the servo head (assuming a dedicated head for early drives), connect it to a signal processing chain and then digitize it. In fact, that's probably something that should be done sooner rather than later, for some makes and models of drives that are dropping like flies now. Then it should be possible to synthesize those waveforms and lay them back down on the platter. Not easy, of course, but similar things have been done by smart and motivated people with, say, QIC tapes. (I'm looking at YOU, AJ!) -Dave -- Dave McGuire, AK4HZ New Kensington, PA
I have a couple Macintosh external drives that aren't working properly. Would it be the right venue to bring them to VCF East to the class? Or should I wait for a repair workshop? Thanks, Eric On Wed, Apr 17, 2019 at 12:36 PM Dave McGuire via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
On 4/17/19 11:46 AM, Jason Perkins via vcf-midatlantic wrote:
Another issue we'll run into is servo tracks, and no way to re-create them once they fade. With the software / fixtures only available at the factory I don't know how we could recreate those tools.
First you'd need to first determine the exact format of the servo tracks. Keep in mind that they may not be "digital" tracks. If the format cannot be determined from patent info, etc, then the only choice might be to temporarily disassemble a functioning drive of the same model, identify the servo head (assuming a dedicated head for early drives), connect it to a signal processing chain and then digitize it.
In fact, that's probably something that should be done sooner rather than later, for some makes and models of drives that are dropping like flies now.
Then it should be possible to synthesize those waveforms and lay them back down on the platter.
Not easy, of course, but similar things have been done by smart and motivated people with, say, QIC tapes. (I'm looking at YOU, AJ!)
-Dave
-- Dave McGuire, AK4HZ New Kensington, PA
I have a couple Macintosh external drives that aren't working properly. Would it be the right venue to bring them to VCF East to the class? Or should I wait for a repair workshop?
Thanks, Eric
Bring those to the next repair workshop. VCF East is not a repair event -- it's lecture-style classes, exhibits/demos, consignment, vendors, etc.
On Wed, Apr 17, 2019 at 12:36:04PM -0400, Dave McGuire via vcf-midatlantic wrote:
On 4/17/19 11:46 AM, Jason Perkins via vcf-midatlantic wrote:
Another issue we'll run into is servo tracks, and no way to re-create them once they fade. With the software / fixtures only available at the factory I don't know how we could recreate those tools.
First you'd need to first determine the exact format of the servo tracks. Keep in mind that they may not be "digital" tracks. If the format cannot be determined from patent info, etc, then the only choice might be to temporarily disassemble a functioning drive of the same model, identify the servo head (assuming a dedicated head for early drives), connect it to a signal processing chain and then digitize it.
On some of the drives I've poked at you can get at some of the servo signals on the circuit card. May or may not be available as analog waveform at convenient levels. The low level head signals should be available on the head cable. None of the drive I have poked at have more than a head amplifier in the HDA. Only a few drives have schematics and hit or miss on if datasheets are available for the major chips. Some of the drives encode data in the servo identifying track and areas outside data tracks. I haven't looked much at embedded servo since its rare in the SA1000/ST506 type drives. I was surprised that the Quantum Q20X0 drives and the Syquest SQ306 use an early form of embedded servo. The SQ306 uses servo with a stepper motor I assume in microstepping mode.
Then it should be possible to synthesize those waveforms and lay them back down on the platter.
Accurately positioning the heads seems like a challenge. I assume you could do some sort of optical position measurement and make your own servo loop to position them. That would require opening the drive.
Not easy, of course, but similar things have been done by smart and motivated people with, say, QIC tapes. (I'm looking at YOU, AJ!)
I think it may be possible but significant work for the first drive and more for each additional make of drive so I don't expect it to become common.
On 4/18/19 9:58 PM, David Gesswein via vcf-midatlantic wrote:
First you'd need to first determine the exact format of the servo tracks. Keep in mind that they may not be "digital" tracks. If the format cannot be determined from patent info, etc, then the only choice might be to temporarily disassemble a functioning drive of the same model, identify the servo head (assuming a dedicated head for early drives), connect it to a signal processing chain and then digitize it.
On some of the drives I've poked at you can get at some of the servo signals on the circuit card. May or may not be available as analog waveform at convenient levels. The low level head signals should be available on the head cable. None of the drive I have poked at have more than a head amplifier in the HDA. Only a few drives have schematics and hit or miss on if datasheets are available for the major chips. Some of the drives encode data in the servo identifying track and areas outside data tracks.
Agreed on all points, and yes the only thing really ever put in the bubble is the head amplifiers.
I haven't looked much at embedded servo since its rare in the SA1000/ST506 type drives. I was surprised that the Quantum Q20X0 drives and the Syquest SQ306 use an early form of embedded servo. The SQ306 uses servo with a stepper motor I assume in microstepping mode.
Ok that's neat, I hadn't heard of a servo-positioned stepper head positioner.
Then it should be possible to synthesize those waveforms and lay them back down on the platter.
Accurately positioning the heads seems like a challenge. I assume you could do some sort of optical position measurement and make your own servo loop to position them. That would require opening the drive.
But if we're rewriting the servo tracks anyway, it won't matter, unless we're trying to recreate them to align to existing data. Otherwise they can be anywhere, and the other tracks will follow suit when the drive is low-level formatted. I guess the question is whether we'd do this to recover the functionality of a drive or recover the data from a drive. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
On Thu, Apr 18, 2019 at 10:24:47PM -0400, Dave McGuire via vcf-midatlantic wrote:
But if we're rewriting the servo tracks anyway, it won't matter, unless we're trying to recreate them to align to existing data. Otherwise they can be anywhere, and the other tracks will follow suit when the drive is low-level formatted.
If its a voice coil servo drive I'm not sure how you would get the track at uniform spacing without some sort of measurement and feedback.
I guess the question is whether we'd do this to recover the functionality of a drive or recover the data from a drive.
I've heard of the degaussing to erase packs problem. I haven't seen bad servo tracks as the reading problem. Is normally some mechanical shift so when the servo has the servo head centered some of the heads aren't on track. Pulling the servo loop method I linked to in the first posting is the easier way to recover the data. I also had tracking problem when I did a board swap to recover a drive. The replacement board servo null was physically off from the original.
Some drives (Apple Widget, Plus Hardcard / Quantum) had a fine position sensor on the head arm. The Lisa disk uses this during a low level format. -J On Thu, Apr 18, 2019 at 10:35 PM David Gesswein via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
On Thu, Apr 18, 2019 at 10:24:47PM -0400, Dave McGuire via vcf-midatlantic wrote:
But if we're rewriting the servo tracks anyway, it won't matter, unless we're trying to recreate them to align to existing data. Otherwise they can be anywhere, and the other tracks will follow suit when the drive is low-level formatted.
If its a voice coil servo drive I'm not sure how you would get the track at uniform spacing without some sort of measurement and feedback.
I guess the question is whether we'd do this to recover the functionality of a drive or recover the data from a drive.
I've heard of the degaussing to erase packs problem. I haven't seen bad servo tracks as the reading problem. Is normally some mechanical shift so when the servo has the servo head centered some of the heads aren't on track. Pulling the servo loop method I linked to in the first posting is the easier way to recover the data. I also had tracking problem when I did a board swap to recover a drive. The replacement board servo null was physically off from the original.
-- Jason Perkins 313 355 0085
On Sun, Apr 21, 2019 at 05:04:25PM -0400, Jason Perkins via vcf-midatlantic wrote:
Some drives (Apple Widget, Plus Hardcard / Quantum) had a fine position sensor on the head arm. The Lisa disk uses this during a low level format.
Found picture of the drives online. Looks like they used an optical position sensor similar to how my RK05's work. This was probably the last gasp of that method before the track density got too high for it to work. Are you saying the Widget only uses it to format? How does it determine head position during normal operation? For my RK05 its always uses the optical sensor for positioning the heads.
It uses the optical sensor for formatting, and if I recall correctly for large head movements. Fine movements are done with servo information on the platters. -J On Mon, Apr 22, 2019 at 7:39 AM David Gesswein via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
On Sun, Apr 21, 2019 at 05:04:25PM -0400, Jason Perkins via vcf-midatlantic wrote:
Some drives (Apple Widget, Plus Hardcard / Quantum) had a fine position sensor on the head arm. The Lisa disk uses this during a low level format.
Found picture of the drives online. Looks like they used an optical position sensor similar to how my RK05's work. This was probably the last gasp of that method before the track density got too high for it to work.
Are you saying the Widget only uses it to format? How does it determine head position during normal operation? For my RK05 its always uses the optical sensor for positioning the heads.
-- Jason Perkins 313 355 0085
On 4/22/19 7:39 AM, David Gesswein via vcf-midatlantic wrote:
Some drives (Apple Widget, Plus Hardcard / Quantum) had a fine position sensor on the head arm. The Lisa disk uses this during a low level format.
Found picture of the drives online. Looks like they used an optical position sensor similar to how my RK05's work. This was probably the last gasp of that method before the track density got too high for it to work.
Are you saying the Widget only uses it to format? How does it determine head position during normal operation? For my RK05 its always uses the optical sensor for positioning the heads.
It's only for relative position; the quadrature approach cannot "unwrap" the phase. The drive logic must have a general idea of where the heads are, by counting the sine/cosine phase wraps as they cross 0 degrees as the head carriage moves. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
participants (7)
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Brian Brubaker -
CT -
Dave McGuire -
David Gesswein -
Evan Koblentz -
Herb Johnson -
Jason Perkins