back to article Techie invented bits of the box he was fixing, still botched the job

Greetings and salutations, dear readers, and welcome to the sunny spot on the interwebs we like to call Who, Me? in which Reg readers share their tales of tech tasks gone awry. Apologies if that bright, cheery attitude is off-putting to you. Your correspondent is experimenting with being a "Monday person" and it feels weird. …

  1. nobody I know

    Oh I remember top loading disc drives well, and replacing heads after disc crashes. (Is it disc or disk?) Initially drives on ICL systems and them CDC drives in Calma CAD/CAm systems.

    Also wondering why it wasn't as late as I though it was when I checked the time on my watch. The drives had very powerful magnets which didn't play nice with a Seiko watch, it was never the same afterwards.

    1. Pascal Monett Silver badge

      Same here.

      I started my career in computing as an operator on a Bull DPS 9. The night shift was where we were doing most of the disk swapping because that's when the accounting packages ran.

      I moved on to programming after that.

    2. GlenP Silver badge

      We had disc packs for the VAXen in my first role, primarily for backup purposes. One issue was if you had to search for something on the backups, as the drives didn't like being spun up too many times in a row. First time this happened the drive died and we didn't have a clue what to do other than call an engineer. All he did was reset the trip - oops! After that it didn't matter how urgent the restore was, we'd tell the requestor it would take a few hours.

      1. jake Silver badge

        Disk packs, not disc packs.

        In that era, a disc was another name for a Frisbee, or a vinyl record (which is where we got Compact Disc).

        Spinning rust was universally called a disk, from the days of IBM's original Winchester drives.

        1. rafff

          Re: Disk packs, not disc packs.

          It really depended on which side of the Water you were. IBM's dominance in Europe was not total, so here they were discs.

          Later we used dis[ck] to distinguish which sort of disc we were referring to. A similar distinction to program[me].

          1. that one in the corner Silver badge

            Re: Disk packs, not disc packs.

            When the BBC Micro gained floppy disc drives, Acorn were careful to include a second star-command to select DFS instead of tape, just in case you typed *disk by mistake.

    3. jake Silver badge

      "Is it disc or disk?"

      The indicated drive uses disks.

      A CD is a compact disc.

    4. Aladdin Sane

      Yeah, unless you're wearing something like an Omega Railmaster or Rolex Milgauss, best stay away from magnets. Even the ones used in knife racks can cause issues.

      1. Jedit Silver badge

        "stay away from magnets"

        Working magnets - how do they fuck (your watch)?

        1. Aladdin Sane

          Re: "stay away from magnets"

          They can slow your watch down so you might end up doing some unintended overtime.

        2. rajivdx

          Re: "stay away from magnets"

          All mechanical quartz watches have a magnetic rotor which is spun around every 1 second by an electromagnet. The electromagnet is very weak or else it would drain your battery in no time. So if you exposed the watch to a strong magnetic field, the rotor will align with the magnetic field and the electromagnet will bot be able to make it budge -resulting in the second hand making half hearted attempts to move from a stuck position.

          This may affect windup watches too if they have too many ferromagnetic moving parts - of course digital watches are unaffected.

      2. Caver_Dave Silver badge

        Between two exposures to lightening! I was very good at demonstrating a similar issue. You could place an Omega or Timex analogue watch in the palm of my left hand, with a straight arm and the second hand would tick forwards and then back every second, or in some cases, it would actually go backwards, but not at 1 second intervals. Found when passing my watch to a very observant person who wanted to borrow it. I was also very good at letting the smoke out of CMOS devices which nearly ruined my career in electronics.

        1. Anonymous Coward
          Anonymous Coward

          > Between two exposures to lightening!

          You lost weight and your watch ran backwards?

          1. Someone Else Silver badge

            You lost weight and your watch ran backwards?

            Sounds like the opening verse to a country song...

    5. Anonymous Coward
      Anonymous Coward

      ICL EDS200 - a whole 200Mb on a very large multi-platter disk.

      They were cumbersome, but could take quite a lot of abuse. Whenever we experienced a brake failure, the drum would spin for ages before we could take out the disk. Quickly learned a highly unofficial trick from an ICL engineer, who showed me how to spring the interlock and manually slow the drum down....

      I don't ever remember seeing an interlock fail. The ICL drives used to have a circle or cross - the circle meant the drive was up to speed and ready for use, and the cross would always flash as the drive span down and go solid when it was not in use.

      Fun times!

    6. I Am Spartacus

      I cut my teeth on DEC equipment

      Still with top loading washing machine type disk packs.

      We had one which kept falling off line, and brining it back required a reboot. These were the days when there was a key that slotted in the top which set the bus address number The microswitches were faulty, so heavy use of the disk, with the heads moving in and out, caused the unit to wobble and shudder just enough for the address to change.

      Oh, how I miss these.

      1. Antron Argaiv Silver badge
        Thumb Up

        Re: I cut my teeth on DEC equipment

        Had a summer job at DEC Westfield, as a test tech on the RK06 disc assembly line. I don't think many of them made it to market, as the RK07 superseded them with double the capacity.

        Best part of the job was that the parking lot backed up against a combined civil/military field. One day, as I pulled in to work, I heard turbines spinning up, so I waited to see what took off. The answer was two F-4 Phantoms, simultaneously, on afterburners. I had my fingers stuck into my ears up to my elbows, and it was still loud (but worth the wait!).

      2. John Brown (no body) Silver badge

        Re: I cut my teeth on DEC equipment

        This guy plays with similar stuff. In that video, the problem is heads going out of alignment when the rubber stops for the heads to "bang" against are perished or missing. Some interesting insights for those who never saw these types of drives before.

    7. Luiz Abdala

      Pedantic grammar nazi alert, just because you asked. And because it is a neat explanation:

      - Disc is reserved for compact-discs, or removable laser readable-writable drives, or round flat objects unrelated to computers;

      - Disk is reserved to computer-used rust platters.

      Or disk is American English, and disc is British English. Even Google can't tell them apart with certainty, but there seems to be a consensus on the first set of definitions.

      So, Floppy disk is fine, compact-disc with the Beatles' White Album is fine. Well, this is not set in stone, but there is some logic in it. Disk was reserved to computer parts, apparently.

      So, a Frisbee is a disc. Those giant, washing machine-sized storage devices rotating at 3600 rpm are disks then.

      1. FIA Silver badge

        Or disk is American English, and disc is British English. Even Google can't tell them apart with certainty, but there seems to be a consensus on the first set of definitions.

        Based on some very unscientific clicking both1 were used in the UK in the 80s, although 'disk' seemed more popular. By the early 90s I suspect it'd largely won.

        1. As can be seen in this delightful advert that shows someone inserting a disk into a disc drive.

      2. JamesTGrant

        Disc is from the Latin, like discus (the throwing object or the fish)

        Disk is from the Greek, like diskos (the throwing object)

        Modern English typically uses disc, coz the Romance languages were considered elegant. But disk was the norm in late 1600s until usage settled on disk by about mid 1700s

        Whereas the Americans typically use disk, coz that was what the English speakers/writers took with them in mid 1600s.

        Helpful? Almost certainly not!

        Interesting? Welp - perhaps!

        1. jake Silver badge

          Regardless, IBM invented the spinning rust-on-a-platter drive, so they got to name it.

          They called it a disk.

          Look on the bright side, they could have called it Platter Storage ... remember, Marketing was already running the show at IBM by that point; they didn't even want to sell the thing at first because they were afraid it would cut into their punch card business.

          1. werdsmith Silver badge

            I liked a fresh shrink wrapped pack of 5 1/4 inch diskettes.

            Often made by a company called Dysan (1973-2003)

      3. Philo T Farnsworth

        IBM saved use the trouble of the spelling ambiguity. We mainframers of the era called them DASD -- pronounced daz-dee. It stands for "direct access storage device" if memory serves.

        But, getting back to the story, sort of, it was a mark of status to have your own personal disk pack.

        1. swm

          Did anyone ever see an IBM RAMAC 305 in operation?

          1. jake Silver badge

            RAMAC 305

            Yes, I saw one used in anger at SLAC. I've got a couple of 126 format B&W pics of me standing in front of it to prove it, in all their awful squareness. Probably taken with an Instamatic, but I honestly don't remember ... somewhat surprisingly, the negs are still good. The pics are dated July 1965.

            I've also seen the one at the Computer History Museum run a couple times. It is supposedly fully operational, and gets demonstrated occasionally. Recommended.

            1. midgepad


              Negatives are very durable.

              One of their positives.

    8. Lennart Sorensen

      I always go by the system that cylindrical tracks are disks and spiral tracks are discs. No idea if that fits any reality other than in my head, but it works for floppy disks, hard disks, optical discs (like compact disc and digital video disc and such) and the other ones I can think of.

  2. Bebu Silver badge
    Big Brother

    "I am not a number," ... MagicSix

    If like me you were wondering about this bit of computing history MagicSix OS.

    The inspiration for the name of the OS apparently was the 1967-68 Patrick McGoohan (#6) ITV series The Prisoner which also made quite an impression on me at that time. I would dearly love to visit Portmeirion but I still have problems with large white balloons. :)

    Be seeing you.

    1. richardcox13

      Re: "I am not a number," ... MagicSix

      > visit Portmeirion but I still have problems with large white balloons

      It is well worth a visit. And is just as wonderfully out of place in Wales and it appears on the screen. To avoid Rover leave just after someone else.

    2. Dabooka

      Re: "I am not a number," ... MagicSix

      Well worth the jaunt, it's really rather lovely.

      I had the pleasure of going last summer although my son and his two friends were not overly bothered about Rover, Lotus Sevens or much else (although the fatality chess game seemed to garner their interest).

    3. Caver_Dave Silver badge

      Re: "I am not a number," ... MagicSix

      They used to have a large white ball/balloon in one of the house windows (going back a couple of decades.)

      We could not find it when we went at Easter. We were there as soon as it opened on a very cold, overcast, but clearing morning and almost had the place to ourselves for the first 45 minutes - quite magical.

      1. The Oncoming Scorn Silver badge

        Re: "I am not a number," ... MagicSix

        Much like the opening minutes of "Arrival" then.

  3. PB90210 Bronze badge

    I was picked to babysit a GEC 4000 computer back in the 80s, in case either of the 2 normal operators were on leave. As it wasn't anything to do with my normal day job (telecoms), I was sent on an in-house training course on one of the testbeds.

    As part of the training, we (there were about half dozen of us) we got to change the single platter 24in(?) disk pack of a whole 5Mb. All went OK until one guy, having uninstalled and reinstalled the pack, tried to start it up... 'ping'... oops!

    1. Roland6 Silver badge

      The one I used (circa 1983) still had boards of magnetic core memory.

      1. rafff

        *boards*of magnetic core memory.

        The core stores I worked with came in a box about 9" on a side. And a whole 6' rack of read/write amplifier boards to drive it.

  4. jake Silver badge

    Stupid "tired operator" tricks ...

    I was burning in some two dozen nodes of T-carrier gear.

    After the end of the ten day burn-in period, one of the final tests was to physically pull the plugs on the redundant power supplies, and then re-insert the plug, before moving on to the next supply. Lather, rinse, repeat, first with the supplies plugged into "power A", and then the supplies plugged into "Power B". A Sun workstation logged the relevant voltages & currents, to be printed out as part of the complete verification package for each machine. I got to the end of the long line of plugs, absentmindedly noted that this plug was different from the rest & unplugged it ... only to take down the Sun box, and completely trash the drive holding the data. It's the only time I ever lost data on a CDC Wren SCSI drive ... and it invalidated the ten day burn-in results for about two million dollars worth of "must ship" gear at quarter end.

    I shouldered the blame, as I had pointed out to my Boss that having the Sun plugged into the test power bus was probably not a very good idea. All I could do is claim exhaustion, working a couple weeks of fourteen hour days because Sales had over-sold production capability and for some reason TheBoard decided we had to make the projected sales figures. Fortunately, my Boss managed to cover my ass & I kept the job. Daft thing is that I wasn't even part of the QA group that managed the burn-in, I was only roped in to help because of a lack of hands ...

  5. Bluebottle

    Split disc

    At one of my jobs we had a Singer System Ten which had 2 washing machine disc drives which boasted split discs - models 41 and 42. The bottom half of the disc pack (2 or 3 platters) was fixed in the drive, and the top half was removable so you could put different top halves on (making sure they were aligned with the tiny locating pin). Very useful for backups. Of course if the top half wasn't exactly located and you managed to remove the lid then yes, a head crash.

    1. Elongated Muskrat Silver badge

      Re: Split disc

      Singer? Sure those were washing machine drives, and not sewing machine ones?

      Alright, alright, I've already got my coat on.

      1. Luiz Abdala

        Re: Split disc

        There is also a Singer in the business of modding Porsche vehicles...

        Midlife crisis cars, beautiful ones.

        1. werdsmith Silver badge

          Re: Split disc

          Also one time part of Rootes Group car makes. Eventually rebadgers of Hillman cars.

  6. heyrick Silver badge

    experimenting with being a "Monday person" and it feels weird

    It's a public holiday here in France, so a croissant and a nice mug of Tetley and no alarm to get up to. This is how Mondays should be.

    (and Tuesdays, and Wednesdays......)

    1. Yet Another Anonymous coward Silver badge

      Re: experimenting with being a "Monday person" and it feels weird

      It's Victoria day in Canada. Nice to see that the French also honour the old queen.

      Surprised that the UK shows such disrespect by not having a Monday off for each ex-monarch.

      1. John Brown (no body) Silver badge

        Re: experimenting with being a "Monday person" and it feels weird

        Last time we had a short week was during one of the big miners strikes and there wasn't enough power to go around. Ah, here it is I don't really recall all that much about it as I was still at school. No street lights and carry torches is about the extent of my recollection :-)

        As for a day off for each previous monarch, I see what you did there :-) I think we'd run out of Mondays.

        1. Yet Another Anonymous coward Silver badge

          Re: experimenting with being a "Monday person" and it feels weird

          >As for a day off for each previous monarch, I see what you did there :-) I think we'd run out of Mondays.

          Well obviously, post-Brexit, we wouldn't have any of those French or German ones

          Just lots of Æthelstans and Æthelreds, maybe a few Cnuts

      2. werdsmith Silver badge

        Re: experimenting with being a "Monday person" and it feels weird

        We have two jour congés in !ay already. Another would be welcome of course.

  7. Ball boy Silver badge

    I remember aligning the heads in those

    An oscilloscope was the weapon of choice: you coupled it to the head and watched the signal peak as you physically moved the arm on its mountings. Ah, those were the days.

    A head crash was quite an event though: I forget the height the heads 'flew' at - about a human hair or so (what's that, about 2 x 10-4 Osmans?) and it didn't take much to cause a head to plough into the platter above or below. In order to do this head-alignment, we had to run packs with most of the covers off, using safety interlock override plugs - so FOD was an ever-present risk.

    1. Antron Argaiv Silver badge
      Thumb Up

      Re: I remember aligning the heads in those

      When aligning heads, it was tempting to rest one's free hand on top of the voice coil magnet. There was a flange on the carriage, to prevent the voice coil from being retracted too far into the magnet.

      Fingers dangling over the front edge of the magnet would be nipped by said flange, if the person doing the head adjustment managed to trip the emergency retract by exerting too much force on the carriage

      (the servo would detect too far out of position and assume there was an error in the drive goes the relay and the power rail is applied to the voice coil magnet.)

  8. that one in the corner Silver badge

    Reminder to self

    I have hanging over my desk at home a platter (14" for a 6.something inch spindle) with four deeply gouged rings, through the rust and into the lovely shiny metal beneath.

    Do try to avoid head crashes, there's a good lad.

    1. An_Old_Dog Silver badge

      Head-Crash Capture

      About a decade ago it occurred to me that PCs were getting quieter and quieter with advancing technology. No floppy diskette drives to buzz upon bootup, silent disk drives, water-cooling systems with quiet fans, etc.

      The modern young'uns didn't know what a "real" computer booot-up sounded like. As I had some old equipment, I decided to make a recording of the sounds. I got my digital audio recorder set up, opened the case, and flipped up the Big Red Switch. Fans on, POST "OK" single beep, disk coming up to speed ... then CLANG!! Clang, clang, bzzzzzhhhhh .... I powered off, stopped the recorder, removed the Quantum Q280 5.25", half-height, SCSI interfaced disk drive and opened it up with no fear, as the warranty was as expired as the company which had made it.

      The top platter had visible spots on it where the heads had impacted. Head #6 was twisted 90° at the end of its arm. Head #5 had been entirely ripped off its arm and was lying in the bottom of the case.

      It's why I cringe when I see fools on YouTube wearing no eye protection, messing about with a powered-up hard drive with its cover off.

      1. heyrick Silver badge

        Re: Head-Crash Capture

        "The modern young'uns didn't know what a "real" computer booot-up sounded like"

        Or being able to tell what speed their connection would be running by interpreting the warbles of the modem.

      2. jake Silver badge

        Re: Head-Crash Capture

        "The top platter had visible spots on it where the heads had impacted. Head #6 was twisted 90° at the end of its arm. Head #5 had been entirely ripped off its arm and was lying in the bottom of the case."

        So you took it the rest of the way apart and made some clocks for important people in your life's xmas presents, right?

        I used to sell 'em at San Jose Flea Market occasionally ... I'd wait until I had a hundred or so stockpiled, rent a space, and sell out in one day at $50 to $100 per, with a few "fancy" models (with blinkinlights and/or set in Redwood burl or driftwood and/or chimes and/or alarm) ranging up to $500. Paid the mortgage for close to ten years doing that. Haltec in Mountain View sold me dead drives at scrap value if I needed them, and would occasionally give me under/behind the counter space to sell them in their store ...

    2. Gene Cash Silver badge

      Re: Reminder to self

      Yeah, a trashed platter or two used to be semi-mandatory decoration for computer rooms and programmer's offices, complete with clean silver circles of doom.

      I remember the first time I was in a computer room and it didn't have one. Felt weird.

      1. John Brown (no body) Silver badge

        Re: Reminder to self

        These days, it's a melted and singed laptop where the battery has suffered a "thermal event" nailed to the wall :-)

      2. An_Old_Dog Silver badge

        Re: Reminder to self

        ... or decorations made from punched cards. The green ones made nice faux Christmas trees.

        Also, don't forget the obligatory 132-column ASCII (EBCDIC)-art banner of Snoopy on his Sopwith Camel, shaking his fist (or middle finger) whilst shouting, "Curse you, Red Baron!"

    3. Roland6 Silver badge

      Re: Reminder to self

      Only gouged, needed to try harder… rippled disks… :)

  9. Steve Kerr

    Don't know the truth in these

    Was told a story of a failure of the fixing for the spindle in a multi-disk platter.

    Think where you spin the handle until it's locked into place when you put it into the drive.

    So the fixing bit failed and the disk platte departed the drive went through the glass top and embedded itself into the ceiling, was told of this happening in the late 80s when I first started work, there may or may not have been someone close when this happened!

    the other story I heard was a computer manager who had enough and brought a gun in and shot the mainframe to death.

    Again, don't know the truth behind either!

  10. An_Old_Dog Silver badge

    Sleepiness is the Enemy

    Zeroing out an old, smallish hard drive:

    dd if=/dev/zero of=/dev/sda bs=16384 [Enter]

    Time passes ... "This is taking a long time for such a small drive.". ... ^C^C^C

    The correct target drive was sdb.

    1. Elongated Muskrat Silver badge

      Re: Sleepiness is the Enemy

      I guess that wrote off your weekend plans.

    2. Uncle Slacky Silver badge

      Re: Sleepiness is the Enemy

      It's not nicknamed "disk destroyer" for nothing...

    3. Yet Another Anonymous coward Silver badge

      Re: Sleepiness is the Enemy

      1, Accidentally connect your terminal emulator to /dev/sda instead of /dev/tty and overwrite your Minix installation.

      2, Decide to just write your own OS to replace it

      3, Profit

      1. Peter Gathercole Silver badge

        Re: Sleepiness is the Enemy

        Or cat a file to /dev/rp0 instead of /dev/lp0 when the system is in single user mode and you meant to print the file.

        ( rp was the disk types for RP03 disk drives, or in our case CDC SMD drives emulating RP03 drives).

    4. Peter Gathercole Silver badge

      Re: Sleepiness is the Enemy

      I deliberately did this to destroy IBM HMC's during the decomissioning of some Power7 775 supercomputers. You would be suprised how long the systems continued to respond. I presume the shell and a number of utilities were cached in memory (although it is possible that it was Busybox providing the shell and other utilities).

      Oh, and before anybody says, there are ways and means to get a root shell on an HMC, if you know the right people in IBM!

      1. David Hicklin Bronze badge

        Re: Sleepiness is the Enemy

        >> IBM HMC's during the decomissioning of some Power7 775 supercomputers

        I think it is a rite of passage when decommissioning UNIX boxes to see how long they stay up for - they are quite resilient usually

        1. Yet Another Anonymous coward Silver badge

          Re: Sleepiness is the Enemy

          "/usr/bin/rm file not found" ?

  11. The other JJ

    Back in around 1988 a client had a PDP-11/44 system with IIRC several RM06 disk drives, similar to the one in the story. One evening they called me in to do an overnight reverse engineering of the ODS-1 disk format to try to retrieve data from a drive.

    The backstory was that one of their PFYs, who already had a reputation as a bit of a cowboy, had swapped the packs for the evening backup, but tried to hurry and crossthreaded the pack leaving it at a slight angle, but the tension allowed the cover to unlock so he didn't notice. Apparently when MOUNT DUA0: was entered in the next room there was a sound like a gunshot as the heads, travelling at several hundred miles per hour, hit the edge of the platters full on. The remains of the heads were vacuumed from the drive bay.

    It also transpired that the filesystem had grown too large for two disks but he'd not had the balls to tell the beancounters they needed more disks, so instead of the A -> B -> C rotation of two drive sets, he quietly swapped to an A -> B -> A rotation of three drives. And the drive he'd trashed was the current copy and its pair, newly formatted.

    They told him not to come in the next day, or the one after that, or indeed, again.

  12. Stuart Castle Silver badge

    Where I used to , work we had a real old school technician. He was an electronic engineer by trade, and had got into computing almost by accident. His employer needed someone to support their new PDP, and he ended up doing it purely as a result of the act he had some electronics knowledge.

    When I first started working at the company, I shared an office with him, so we got talking. I also got used to the smell of burning, and the slight pop as something he was working on either exploded or caught fire. His electronics knowledge came in handy a fair bit. We operated several computer labs, and needed wierd bits of hardware more often than you'd think. He built his own Ethenet cabe and socket tester, which didn't do anything that you couldn't do with a low end commercial tester. It *did* cost a lot less though.

    Another project involved a video editing lab we'd set up. Because students frequently needed to capture video (analogue only at that time), we needed the students to be able to plug and unplug stuff at will but we didn't want them messing around at the back of the PC. We had £5k broadcast quality capture cards, we *really* didn't want the students messing round with them.

    So, this technician designed quite need breakout boxes. The box offered composite video, s-video, line level stereo audio phono sockets. It offered all that in both inputs and outputs. It also had a stereo 3.5mm headphone jack, which was amplified. A neat, if not exactly pretty, unit.

    He also dabbled a bit with scripting, but wasn't always careful. I noticed one day that a lot of the software i maintained in the lab had started complaining it wasn't installed properly, or otherwise malfunctioning. This was preventing tutorials, so I had to solve it ASAP. I would also have to notify my boss because there would have been complaints.

    After comparing a fresh install (done from the original disks) of one of the applications that was failing, with the install that was failing, I noticed that the failing install had no image files. No JPGs, No Gifs, No Pngs. This was what was then called "Multimedia" software, so the image files were part of the install.

    Concerned we had files going missing, so therefore concerned we had a virus on the machines that was somehow being missed by the anti virus software we used, I talked to all the technicians, asking if they'd noticed anything..

    That's when this technician stepped forward. We had a problem with the machines having too small a system drive (for whatever reason, we used an image with a tiny C drive and a D drive taking the rest of the space, and had the applications installed on the D drive), and he'd noticed that students, as they were browsing the internet, were using a lot of space on this drive, so he wrote a script that over night, logged on to each machine in the lab, copied any images to his machine (yes, for the reason you probably think), then deleted the original. When I complained, he altered the script to limit where it looked.

  13. Jotrav

    When I joined DEC in 1977 one of the first sites I visited had a couple of RPR02's, a whole 20Mb each, and I recall being advised that head positioning was based on a mechanical ratchet. Significant entertainment occurred when this ratchet became worn... Regular backups to magnetic tape were an essential recovery activity, and often required.

    However, I cannot remember which OEM the drives came from before DEC slapped a badge on the outside. To be fair, that was most of half a century ago, I must be getting old, or something like that.

    1. An_Old_Dog Silver badge

      Disk-Head Positioners

      The Data General 6045 drive unit (5 MB fixed platter, below, and 5 MB removable cartridge, above) in my Nova 4 had a nifty disk-head positioning system. A large voice coil drove the heads back and forth. There was a very bright light which shone through a glass strip attached to the moving assembly. The glass strip had a pattern engraved upon it. On the far side was a photocell hooked to an op-amp which did (IIRC) differentiation on the rate of received light pulses. The op-amp's output fed into a circuit which determined when the current to the voice coil should increase, hold steady, decrease, and change direction.

      Knowing which the track the moving head assembly was starting from, and which track it was to go to next, the controller maximized the acceleration and speed of the heads while preventing them from overshooting the track they were moving to.

  14. Martin-73 Silver badge

    I don't even work in IT

    But ffs, everyone knows what a disk pack is, it that which shall not be touched unless by the anointed ones.

    1. Martin Penny

      Re: I don't even work in IT

      "And lo, it was written than none but the BOFH or his designated PFY may enter the Holy of Holies, the Inner Sanctum of the Server Room, lest thee encounter a non-signed trip hazard or receive a bolt-from-the-blue."

  15. ben kendim

    Yup, been there, almost done that!!!

    Summer of 1978, I opened the still spinnning disc drawer on a 360 with inoperative interlock. Scared the heck out of me. I did not reach in to unload the disc pack, just stepped back from it... I was an intern, and was worried about being sent home.

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