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Write Bits Directly Onto a Hard Drive Platter?
kidcharles writes "I'm working on a project that requires writing bits to a magnetic hard drive platter in a completely controlled fashion. I need to be able to control exactly where 1s and 0s will appear physically on the platter. Normally when data is written to a drive the actual bits that get written are determined by the file system being used, as modified by whatever kind of error handling the drive itself is using (e.g. Reed-Solomon). All of the modern innovations in file systems and error handling are great for reliable and efficient data storage, but they are making my particular task quite daunting. My question for Slashdot: is there a way to get down to the 'bare metal' and write these bits? Any good utilities out there to do this? Obviously a free and open source solution would be preferable, but I'm open to anything at this point."
The stuff Spinrite does stopped working 15 years ago. On modern drives you're pretty much doomed. Considering Gibson has been known to rip off SYN cookies and spout such nonsense as "Windows RAW sockets are going to destroy the internet", I wouldn't go anywhere near him for advice.
The cynic in me wonders if he is working for some hack start-up company trying to develop a DRM scheme for a hard drive, similar to the crap the studios do to DVD's to make them difficult to rip. Typically this involves creating some sort of currupt/invalid area on the disk that your particular device will know to ignore, but will lock up anyone else trying to read the data off the drive.
The optimist in me wonders if he is trying to defeat such a scheme.
We don't need to work like that any more.
The submitter appears to know enough about what he's asking to know that it's also impossible / completely impractical. Recording ones and zeros directly isn't done for a reason, submitter appears to understand this.
Keep in mind that the question is not just why the submitter wants to write directly to the magnetic domains of a hard disk, but why the submitter asked the question of how to write directly to a hard disk.
I can think of a number of reasons for the latter:
- The submitter could be an author writing some cyberpunk techno-thriller, and wanted some technical feedback from the 'experts' on Slashdot.
- The submitter could be a CIA drone trying to write a report on how it's impossible for the terrorists to somehow 'hide' data on hard drives that even 'dd' can't read.
- The submitter could be a troll.
That's just off the top of my head.
On the other hand, I seriously can't think of a good reason why anyone would want to actually damage a hard drive that way. If all you wanted to do is very precisely create a surface with a complex pattern of specifically oriented magnetic domains, there's easier ways. For example, there are equipment suppliers that can provide high-precision two axis steppers with ready to use computer control interfaces. It's not hard to get equipment that'll go down to atomic precision.
The submitter doesn't appear to know enough to say why he wants to do this. If this were a consulting job, I would say, what are you really trying to do ? My guess is that, whatever that is, there is a better way to do it.
A whole chip? Really? That sounds hard. Just Ebay an old 20MB Seagate ST-225 MFM drive, and write whatever bits you want. It doesn't know any better.
Or, the submitter could contact Seagate or another drive manufacturer and ask what it would take to get a drive with special firmware that let him write 1's and 0's directly to the drive wherever he wanted. Basically, remove the intelligence on the drive.
It's not that impossible for drive manufacturers to do things like this for you, if you have the $$ to pay for it. I don't know what the cost would be, especially since he's really only [probably] looking for a few drives for this project. If it's grant-funded research, the grant would pay for it. If it's an independent project of some kind, he's in for a surprise.
I took a behind-doors tour of a major drive manufacturer a few years ago. During our visit, we were able to visit with engineers - one of whom was head of the firmware engineering team. He told us lots of stories about the firmware requests they've fulfilled. One example was a customer who supported lots of old PBX systems. These PBX systems ran software from a hard drive, but due to the age the system only supported drives up to (around) 200MB. Nobody made drives that small anymore, so this drive manufacturer re-wrote the firmware for them ($$) so a 120GB drive (the smallest they made at the time) would only recognize & address the first 200MB.
So yeah, I'm sure a drive manufacturer like Seagate could write custom firmware for him that would meet his project needs.
- Submitter wants (for whatever weird project of theirs) a surface with magnetic image on it (a'la LightScribe, only magnetically).
- Submitter missed the actual point, and wants to write raw data to drive (some embedded project) circumventing partitioning and filesystem overhead - quite frequent.
- Submitter wants to record a lot of analog/unreliable data - skipping error checking and using the extra space to store more data (errors = acceptable noise)
- Submitter doesn't care about data storage and wants to use disk heads as a very fast magnetic field sensor/generator
This is quite doable with ANCIENT pre-ATA drives. The computer controlled everything then, the head position, the moment of writing and so on.
It is doable with old ATA drives that run PIO modes, probably with a bit of electronics tinkering.
It is about impossible with modern drives. You'd have to replace the whole electronics with your own and drive the head and the motors with your own.
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It would be nice to know why the poster thinks this feature is important. The only things I can think of is the following...
He is using parts from a hard drive to make a robot. So he wants to control a Robot using the hard logic board, to control the mechanisms.
He is using the high speed nature of the drive and the noses it makes to make a speaker out of it by moving writing bits in the right spot.
Trying to make a full real-time application.
Researching better algorithms for drive storage.
Attempting to make some sort of digital watermark on the drive.
The first two are just silly hacks which would get geek creds but not overly useful.
The Real Time System You probably need more then off the shelf and free software to do the trick
And the Research you could probably program a simulator to simulate the results.
The Watermark idea will work until someone fills up the drive.
So I would agree with the poster unless you come up with a good reason where there isn't an other approach I don't see the need to do this.
If something is so important that you feel the need to post it on the internet... It probably isn't that important.
Since the intricacies of the drive's physical address space are not accessible from the outside, there will never never never be a reason to try and fiddle with it directly. Because you can't.
Careful there. I know you're addressing a typical user of the hard drives, but there ARE ways of -- and reasons for -- getting at the "bits themselves". One of my colleagues, as a fresh student at one of the National Labs in the US, was tasked with recovering data from a crashed (literally crashed, so that the controller was destroyed and platters bent, with lots of data loss) disk. Of course there are ways and means of doing so, usually involving fantastically specialized equipment and lots of expense (and, often, the complicity or orders at the Federal level).
He ended up building a sweet little system which could scan the surface (in a low-level clean-room, of course), albeit slowly, and interact directly with the bits.
I'll have to ask him how they figured out the filesystem, the error-correction, and so on, without any of the usual partition tables and so forth.
I'm surprised by the number of people who seem hostile to this question, mostly because they can't imagine any circumstances where they would want to do this. I can think of several. In fact, I was thinking about something similar with optical disks just earlier today. (I'm curious whether small holograms could be created by writing an interference pattern directly onto a CD or DVD, but I would need exact control over how the tracks lined up to achieve this.)
Here's some concepts just off the top of my head:
* He's come up with a new disk encoding scheme, and wants to try it out.
* He's doing research into how long disks retain data, and is questioning basic assumptions like whether surface bits permanently magnetize the platter underneath, affecting later bits in the same location. Or how far the domains spread.
* He's working with self-assembling molecules and needs to give them a patterned magnetic surface to build on.
* He wants to 'print' a 2-D picture onto a small portion of the hard drive, and bounce a laser off it. (The magnetic alignment of the surface domains would polarize the photons slightly.)
* He's making a high-resolution rotational position encoder, so by reading across 32 tracks knows the rotation of the platter down to a few nanoarcminutes.
* He wants to totally destroy the contents of a disk. (I assume this is what most of the hostile people think is the intention, presumably as the payload of some virus)
Those are just the ones off the top of my head.
However, the ranting people do have a point that without knowing WHY you want to do this, we can't really suggest the best solutions. A lot of people have recommended going back to super-old MFM hard drives that allowed this, but we don't know if you require the density of modern hard drives.
To do this with a modern drive, you're basically going to have to rebuild the controller. Either totally remove the controller board (leaving handy raw connections to the stepper motors and drive heads) or cut the connections between the microcontroller and the low-level electrical functions of the drive, and substitute your own. Here's where knowing your accuracy requirements could have help, because if you want relatively large bits, you can get away with fairly low-frequency components. A 20Mhz microcontroller can, with say an external high-speed shift register, push out an 80mbit/s serial stream, which equates to >120,000 bits around the track of a 6,000RPM drive. Not quite the same density as the manufacturer, but better than the old MFM drives.
Your next problem is going to be this: It's really, really hard to tell where the head is on a platter. I've no idea how modern drives do it, but it used to be done with 'marker' bits either in the track, or on a nearby 'index' track, plus a little timing. Preserving these location marker bits is actually the most important job of the drive controller.
It's not impossible, merely very difficult. I could probably make one with only several weeks of hard work.
Alternately, you could try getting into the firmware and re-writing it to your specifications, but that might take longer. You would have to reverse-engineer a lot of stuff that is specifically hardened against this, but at least the hardware would be stable.
Jeremy Lee | Orinoco
I was stumped as to why one would want direct access to the drive like that, until I read your post. Thank you.
But I also agree that this is just about impossible, depending on what he's trying to do. There's no way he can control the heads of the disk: too many layers of abstraction exist between the user and the hardware. But it should be possible to control where data is placed on the disk: this is what disk defragmentation does, after all.
But even then I'm not sure that what the device reports is necessarily what happens on the platters. Flash memory drives, for example, relocate information to balance the number of writes and extend the life of the drive.
I would recommend contacting the drive manufacturer and then making my own block device driver for Linux based on their recommendations. But even then I'd question the core reasoning: is this really, really necessary?
What you say is all well and good, but you don't think that knowledge of that purpose might help with the solutions?
It's nothing like that at all. It's more like that-won't-work-so-what-are-you-trying-to-achieve-maybe-something-else-will-work, which is fair enough.
A lot are asking "Why do you want to do that?", which sure looks like curiosity to me.
Confucius say, "Find worm in apple - bad. Find half a worm - worse."