Magnetic Media (Floppies and Tapes) – Computerphile

Magnetic Media (Floppies and Tapes) – Computerphile

So I thought we’d look at today is how do pop adidas hardest tape store information they all store the data but in terms of electrical signals in silicon, but as basically magnetic data stored on bits of spinning rust So what I’ve got here is a five and a quarter inch Floppy disk this one’s got a copy of small talk on it Probably for PC. It’s what small talk small. Talk is the the classic Object-Oriented programming language then what about object-oriented programming then look at one of our arrow videos This is not the word saver icon. This is actually a three and a half inch floppy disk Which is what people are probably more familiar with? Essentially this and this work in exactly the same way That’s just easier to see what’s going on and why they’ll call floppy with one of these when these are produced they put a protective Hard case around the floppy disk and a mental cover to protect the actual floppy Information there so it’s easy to see why these are called floppies if you actually take them apart and here’s one I destroyed earlier. This is a five and a quarter inch floppy They’re also eight inch floppies, and if you actually take it apart, you’ll see this is a sort of protective plastic case there We are in and inside that there is a sort of material thing that’s actually there to protect the floppy disk Which is this bit, so when the iBm originally created the floppy disk? They originally just had the floppy part like that But they found that dirt and things would scratch it and Destroy the data So they put it in a protective case so that only the readwrite area was exposed to protect the data and the material side Just sort of mopped up any adjuster got in there and stopped it scratching the data and it is literally just a piece of plastic coated in Effectively rust is probably a cobalt based compound rather than iron, but it’s basically rust. It’s magnetic data I knock so Just like a classic cassette tape or a video tape that you may have used so what have we got well we’ve got a magnetic Material and the way the computer would use this is actually easier to see with tape so computer tape effectively, the same sort of things is a classic tape you may have seen these in sort of old movies sort of sitting in the background turning and that’s exactly what they did if we take the Casing off you have an even thinner even floppy a piece of tape than the actual Proper disc and you can start to see why tape is even still used today because it just holds so much data you think about it the amount of surface area that you can write to on a floppy disk is only going to be a small amount of Tape that you need to store the same thing and yet if you think about the size of this you can get a lot more tape Into the same area well that’s someone else do the math on that so you have the tape and you have one side of it got all your data on and another one going to the take-up spool just like an Old reel-to-Reel audio cassette and then you would have a head and I’m going to use the pen to represent the head of the machine Which would sit in contact with the tape and the tape would be pulled across the head as it was Transferred from one spool to the other and that head could either read the data that was on the tape or write the date on The tape and how is actually arranged depends on the tape format? We won’t go into the details, but you could basically store bits of information Sequentially on the tape so you start off with the first bit here say than the next bit and so on and as you read through the tape you would store more and more information as I said the Order on the actual day two depends on the tape format This is general principle and as you read through it you get more and more the data Was it would it be one one-line thick or would you be using multiple tracks? There was various different formats. I mean this is nine track tape I think I’m not entirely sure what you sort of had nine track Tape formats you had other ones some of them use helical scan were actually the head is spinning itself and so it’s writing stripes across the actual tape like a video cassette does These various things some are linear when they’re ready writing in that though actually it literally depends on the tape format most common one today Is called Linear tape whether it’s actually still linear I am not certain So you can store a lot of information on this But you have to access it effectively sequentially you have to start at the beginning and move through to the end before you can get To any information that you want on it Which of course takes time if you want the information right at the end here you? Have to spill out all the information on the tape and you can do this relatively fast and Shawn’s going to wind all this back up later So only works you have to access things sequentially you don’t have easy random access to the data You could do it You could get the computer to sort of work out where how far needs to fast forward and then put markers in the data So you can find different bits, but you still have to wait while it gets to that point? To access it What we disk work? In Roughly the same manner to record Data. I’ve got a floppy drive here which I’ve taken apart Eagle-eye viewers may recognize it you still have The heads just here the disk is Popped in and you manually have to close the thing down to lock the disk in place And then there’s a motor which spins the disk ground So the disk is spinning round and round around very fast like a cD does so the really important thing is that the head? Can move backwards and forth? Over the top of the floppy so we have two axes of movement here We have the disk spinning, and it’ll go in One direction Let’s go that way which means that the head is getting the data in a loop So it’ll get some of the data as it goes around and round around around and they’ll come back again you can start getting the data again, but the head can also move backwards and forward along The dryer which means it can step out or step in to different parts of the disk and so get a different loop or different? Trackers, they’re known of Information from the disk if I can draw a circle which I can’t hurry up, so this is a disk So we’ve got the head going up and down which means it can draw Tracks around with this as I said I can’t draw circles. Just one more and so the head can step out To each of these track and read a different set of data at each of these different points So protocol this track 0 this would be track 1 this would be tracked – this is the track 3 and this would be tracked 4 so we’ve now got 5 tracks of information where we can store data So where’s on tape we have one long piece of information? And we have to scroll backwards and forwards in it with a disk we have lots of small tracks of information, but the sort of consent along the disk surface And we can step our head to read one of these tracks and because the disk is spinning probably with a floppy like one of those at 300 rPM with a modern hard disk which works in exactly the same way at 7,200 rPM. We very quickly get all the data that’s stored on their path under the head in one go so we can specify Which track we want to read the data from and we can move our head to the right point? But we actually go one step further because we actually break the data up into what we call sectors like so And then hami ok I’m not an artist looks like a giant spider’s web. It’s not yeah I mean, it’s the same thing you bisecting the Circle into several slices, we’ve got 1 2 3 4 5 6 7 8 9 10 we have 10 sectors So we say that the data we want to access is on track to Set to 8 and we go to Track 2 and we wait as this spins around until we get the data for sector age Read across and then we might say we actually want the data from track for sector worn so we wait until the Data for sector 1 of Track 4 comes across So if we go back to the drive if we put the disk with our drive on a diagram here And we eliminate it. We’ve got the sector’s around here. The disk is spinning Very very fast so the head just moves Backwards and forwards and say so it’s down there their position for track 1 and it waits until sector To say comes across reads the data and then send it out to the computer or take the data from the computer and write it Onto the floppy and so because of that we can access any particular sector of data We want to on the disk because of the nature of a circle surely the inner tracks store less data than the outer tracks so yes They will or maybe they won’t it depends on how the disks formats the information a standard sort of PC floppy The inner track store as much data as the outer tracks because the disk is spinning it’s not Distance it’s an angular velocity, not air So it’s got a constant angular velocity So it takes the same amount of time to go around once all that means is the data is packed into a smaller thing But it out at the same speed it probably means the Data is more Likely to get corrupted on the inner tracks rather than the outer tracks on something like a five and a quarter inch floppy Probably depending on the type would either be storing 256 Bytes, Maybe 512 bytes of Data in one Sector of the same on a three and a half inch floppy you’d have 512 byte Sectors, and actually your hard disks work in exactly the same fashion they have tracks They have sectors and they also have different heads and the other thing you get in the hard disk is you just have multiple platters And the reason they’re called hard is because they’re made out of things like glass rather than after flexible bits of plastic We keep carving away at this and what we’ll end up with is something that looks nearly like a cube So we probably may be a bit a bit of extra there and a bit of extra there and there, but we’ll get it We’re getting there, okay. Now some objects obviously are more amenable to miss than others, but the more images we get the better it is


100 thoughts on “Magnetic Media (Floppies and Tapes) – Computerphile”

  • Ze Rubenator says:

    All the CRT's make this video impossible to watch for me. There's a constant high-pitched tone all the way through and it makes my head explode.

  • Maizuma Games says:

    I'm kind of disappointed. The guy spend a lot time describing how things rotate and how heads magically read magnetic data… I was expecting to hear about the actual read/write process. Sensors and precise numbers, speed comparisons, etc.

  • rchandraonline says:

    While Compact Discs start at the spindle and spiral outwards, the numbering of floppy and hard disk tracks generally starts at the edge and increases towards the spindle.

    Audio Compact Cassettes (audio cassettes) normally have the supply reel on the left and the takeup reel on the right. The shown animation must be of a reversing deck 🙂 Love those autoreversing ones; gets to the end of the tape, senes the reels aren't moving, flips the head around, and starts rotating the reel on the left and the capstan in the opposite direction.

  • Wish he'd talked more about variable sector/track drives. Apple used those in the early macs, and they sped up as things went along, producing a distinctive musical effect!

  • NotMarkKnopfler says:

    Great to see smalltalk mentioned. As the first object oriented language written in itself it was decades ahead of its time. Even now there's nothing quite like it. It would make an excellent subject for a video.

  • On the back of my 5 1/4 disks there's a pictograph saying do not store under 10c. Will freezing the disk really kill the magnetism?

  • Alexander Roderick says:

    Music CDs were designed for constant linear speed, so the disc spins at 200 rpm near the rim and 500 rpm near the center. This wasn't a problem for music all read in order, but when you got to CD-ROM the drive would speed up and slow down constantly when it skipped around the disc. Eventually the constant speed drive became standard, and the drive would just read data slower closer to the center rather than speed up.

  • How does the drive know which sector it is reading? Is there a special area somewhere on the disk that it can detect as it goes round?

  • Seems kind of unfortunate though, that you read and write with angular speed, rather than surface area on the disk…

    But I guess it would be more complicated and probably expensive in terms of parts to vary the rotational speed of the disk…

    Because right now the theoretical limit of the information density on the disk, is determined by the track/sector closest to the center of the disk.
    Guess this would also make for a fun math problem in which you put number of tracks vs the writing desity and see which settings gets you the largest data capacity for the full disk.

  • In a late 90's computer magazine I saw a review of a device that'd let you store data on a VHS tape. It let you store quite a large amount of data on a relatively cheap format, but the machine was expensive and it was slow as molasses.

  • Don't forget the Exatron Stringy Floppy. An ultra-thin, continuous loop cassette.

  • Jan Sten Adámek says:

    Fun fact: all floppy disks are double-sided. 3½" disk drives have two heads so they use both sides. But 5¼" ones have only one head and you could write only on one side because the other was mechanically marked as read-only. But if you punched a hole in the diskette with a special puncher, you could then write on the other side as well.

  • IIRC the Apple IIe floppy drives used a variable-speed spindle for its floppies so the outer cylinders could have more sectors per track.

  • I just dug out my old C64 the other day. It's so funny to work with actual "floppy" discs again. I even enjoy the awkwardness of it all 🙂

  • Please, a followup video to show how magnetism is used to turn bits on and off, and why magnetic tapes/discs deteriorate over time.

  • Helge Frisenette says:

    BS. A hard disc is much more involved than a floppy. The track alignment alone is just amazing in that it not only works, but is also robust. It's like saying an LP and a CD works the same. Might be true in a very general sense but there is a world of difference in the actual implementation.

  • Björn Dahlberg says:

    i'm still having nightmares about installing Windows with floppies and one of the last one is damaged…

  • Chaitanya Shukla says:

    All of a sudden I feel I am old wathing this video. I have used those old floppy disks and magnetic tapes regularly on my old pc which was powered by a Intel Pentium(100Mhz ) Cpu. In my company I still use magnetic tapes for backups as they are lot more reliable than hdds and ssds.

  • Zeedijk Mike says:

    I almost became nostalgic while watching this video.
    Brings back good old memories when installing AutoCAD using 30 3.5" floppies on 25 PC. A good days work 😅

  • It doesn't matter who we are, what matters is our plan. says:

    And now I can have a MicroSD card the size of a pinky nail holding 128GB of media delivered to my house in 24 hours. I feel like we can't fully appreciate current tech unless we've all tried using floppy disks.

  • Is there any technical reason why optical media like CDs only have one long spiral track while magnetic media like floppy disks or hard disks have many circular tracks?

  • I've still got more than 160 analogue VHS tapes, and a working VCR. All of them my own recordings from German TV, roughly from 1995 to 2005.

  • Guðjón Ólafsson says:

    We had a silly joke once: Did you hear about the computer virus called Viagra? It changes your floppy disks into hard drives.

  • Wicked Mouse says:

    I was hoping to see an explanation of the technical side a bit of magnetic data as well, on a molecular level. I know that these pieces of rust on the tape are like small magnets and the direction they are standing defines whether it will be read as a 1 or a 0, but would have loved to see a more in-depth explanation.

  • On modern hard disks the outer tracks do hold more data, unlike floppies…
    if you measure the speed of a modern HDD, data near the start of the disk will be read or written faster than near the ending…

  • icedragon769 says:

    Oh, man, there's a super high-pitch squeal in all Dr. Bagley's audio. I want to watch but it actually hurts a bit.

  • Ryan Burnside says:

    One thing I like about technology is that it doesn't really get outdated. Sure the actual devices might become obsolete but the knowledge that makes them work the real "technology" can be used in strange new ways any time it fits the bill. It is very frustrating how careful marketing has directed consumers' definitions about technology. It's not the device, it is the study of the principles that make the device work. Too many people say they like technology but really just love consumer devices and would be bored to tears learning the technology itself.

  • Seth Roughani says:

    Hard disks can also be made of aluminum or ceramics, anything non-magnetic so eddy currents are not generated.

  • 100 years from now, archaeologists will come across this video and scream at destruction of archival material.

  • You missed the best part! you didn't record the glorious operating noise!
    That kachunk when you insert a 3.5" is so satisfying

  • Fernando Deveze says:

    If you do a follow up could you explain how does the new japanese cd's and cassettes store more data than a normal crystal one. Thank you and great video.

  • ɐɯɹɐʞ ɐıuɐɯ says:

    at 8:38 How is that connected to previous question?
    It answers why read/write speed is the same for inner/outer tracks, not how much data is stored.

  • Phil Boswell says:

    Wow, SMALLTALK/V 😉

    It is not impossible that I sold him that floppy disk while I was working for the company that imported it into the UK!

  • This is awesome! Now I'd love to see a video explaining how SSDs work—or would it be essentially the same as the video on "How Computer Memory Works"?

  • goeiecool9999 says:

    I would like to see a followup explaining more about the read write mechanism. And also an explanation of why punching a hole makes a disk double sided.

  • 666Tomato666 says:

    5.25" floppies? such newfangled stuff! you couldn't launch even nuclear rockets with those! 8" floppies is where it's at!

  • isaacsailor1 says:

    Could you do a comparison between HDD and SSD data storage methods? Is there a why to visually describe the disk access speed between the two storage types?

  • Rust is specifically iron (III) oxide; while if any iron compound is used in a magnetic coating, it would most likely be iron (II) oxide, similar to magnetite.

  • It was really interesting but I couldn't finish it. There's this high pitched noise in the soundtrack and it's making my head hurt.

  • Yep, linear tape is still a popular format. The most common format these days is LTO, or Linear Tape-Open. Modern, generation 7 LTO tape carts can hold up to 6TB of uncompressed data, with 12, 18 & 48TB capacities on the horizon. LTO cartridges have only one spool, so the tape drive contains a take-up spool internally. Data is written on the first track from the beginning of the tape to the end, then written on the second track from the end back to the beginning. Data continues to be written in this serpentine fashion until all tracks are full, and the tape has been wound back into the cart.

  • Back in the day, I worked on a PDP-11 system which employed a TU-58 tape drive. The media was "block structured". These tape drives were also present on all VAX-11/730 machines to load the microcode during boot.

  • Richard Dale says:

    Would have been interesting to know how the data is actually read and wrote to the magnetic media. How it physically reads the disk I think most people already knew.

  • Edgewalker001 says:

    I grew up actually USING those, like, to store things on.
    I had a bag of 3,5s with loads of little applications on that I brought to school so I could mess around with them on the public workstations during recess… =p
    And before that I had a C64 with a floppy reader, my parents didn't have enough money to buy me a Super Nintendo so they got me one of those instead (Just kidding, I had a Sega Genesis too =p).
    Here in Europe the 3,5 floppies were called diskettes and the larger ones were called flex disks though.

  • Edgewalker001 says:

    So basically, file allocation tables are literally bits of data that tells the computer where on the physical disk to look for the information in an actual file?
    I don't think I never really understood that until now.

  • the large floppys are great for storage. specially for cd's.
    I hope to see videos about optical and flash storage

  • Oh god I can hear the CRT displays. Even through youtube's compression, the audio capture, and my speakers, i can still hear them…

  • My lab partner worked at NetApp, said they've only replaced their tapes archives a couple years back…gotta ask why? Is the speed differential between magnetic and silicon storage not drastic enough to justify the replacement price? We still got hard disks on the market so I presume the answer is yes, just wondering if there's anything in the future of magnetic storage, or if SRAM will eventually absolutely replace it….

  • Strange that the floppies didn't originally have cases.

    Looks like something has gone wrong with that Apple II in the background towards the end.

  • That tape holds 170 megabytes, not so much by modern standards. The nine tracks store eight bits and parity so it is not like one reads first one track, then another.

  • Ghost Emblem says:

    am I the only one who didnt understand why the inner portions store the same amount of data as the outer portions?

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