Debugging the 1959 IBM 729 Vacuum Column Tape Drive at the Computer History Museum


Our magnificent IBM 729 7-track magnetic tape drive is giving us read and write errors. We attempt another heroic repair. Which is a great excuse to take a close look at its amazing innards. Looks like nothing in the video, but just putting the 3 brush blocks back was a 3 hour operation with mostly 6 hands at a time inside the drives – including mine, which is why there is no video documenting it. Hence the clapping at the end, we were quite relieved we did put it back together correctly!

Tape capacity is around 20 MB at the highest (800 cpi) density setting. Actually quite respectable if you compare it to this machine’s main memory (16KB).


Special thanks to Samtec for fabricating and donating the IBM-spec special wire. Extra special thanks to Shashi Chuganey for spooling the wire from scratch at our Oregon facility, and to Raymond Lee for silver epoxying them in our clean room facility in California. Also thanks to CHM docent team member Dave Bennett for finding a commercial source of replica brushes. So I didn’t have to do the 92 production ones after the first 8 hero prototypes…

Many more people were involved in getting these tapes operational, but limiting ourselves to the ones that appear in this video:
Ignacio Menendez
Glenn Lea
Carl Claunch
Stan Paddock

Related Links:
Official video of our IBM 1401:
Period video introducing the IBM 1401:
Robert Garner’s blog article about the restoration:
The restoration team’s hardcore technical website:

Our sponsor for PCBs:
Support the team on Patreon:
Merch on Teespring:
Learn more on companion site:
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  1. Frances Bernard says

    Looks a little more like a 'modern' instrumentation technology classroom at N.A.I.T. than a computer room now doesn't it? In other words, the mechanical parts behind the more 'modern' computers sitting at desks for people to run our oil field instrumentation systems that are still running in some oil field facilities and in some switching to another mode of transport of oil products is lagging very far behind the proliferation of the numbers of computer languages always being invented so fast now [700 last count] so now few people can keep up now when tryiing to do the budgeting math for AMCO.

  2. Siamak Aghazeinali says

    great video . i was use to watch this computer in old movies and it was showing advanced technology now it looks like a joke! i am astonished if you compare with new computer how much was capacity and ram and speed. ?

  3. FerdinandFake says

    Why would you ever need special wire to run a brush for a simple magnet???

  4. Pilot Paul says

    Is it me or does this remind me of aperture science in the 1970s

  5. Buff Barnaby says

    On Mannix they use colored reels that look so cool , and a punch card comes out with his name on it.

  6. Buff Barnaby says

    Who had the brainpower to design a machine like this ??? Unreal.

  7. Buff Barnaby says

    Voyage to the bottom of the sea had computers like these onboard submarine LOL

  8. Saskia van Houtert says

    Carbon-brushers are also needed in washing-machines, mine is repaired. Nice to see them made.
    Kind regards.

  9. Saskia van Houtert says

    Mainframes from old history, perhaps a new one can be made with a plotter then we have for example a new Matrix-mainframe. Who can design one ? Remarks are liked. Kind regards.

  10. Paul Cohen says

    Tape drives I worked on in the seventies were much better.
    They had capacitive coloum position sensor in a bridge config.
    That made positioning with servomotors much faster quieter and accurate.

  11. Paul Cohen says

    From where you got the carbon rod?
    What are the specs?

  12. SteelRodent says

    8 motors in these old things… modern LTO units usually have 5-7 motors depending on who made it. Despite of how much faster the modern drives are, they really haven't gotten much simpler, just a bit smaller.

  13. Rubbishcop says

    Is that conductive epoxy you used in the back of the new slip ring clutch brushes?

  14. Edgar Vega says

    omg it's the computer room from tf2 2fort

  15. percival23 says

    The sound of that computer room brings back memories. They even have the raised floors …love it.

  16. Jimmy_James Jams_A_Lot says

    I had never considered, just how much ‘mechanical’ goes into the more modern computational rigs. And more recently even, it is not at all apparent until you try to change your ink cartridge, or even more applicable is storage devices. Mechanical engineering really is a precursor in all things electronic, to where we’d be nowhere if it weren’t for our ability to predict the mechanical implications of anything. SO AWESOME!! You know what you’re doing is important when the World wants you to film every minute of it!!

  17. Leo Gonzalez says

    trying to figure out Marcs accent is he German??

  18. arjovenzia says

    very cool. I always wondered how the old tapes you saw in the typical Hollywood 'computer scene' were out of sync. I always thought it was a camera artifact or something. vacuum feed, thats so cool

    I also very approve of having to use a lathe for repairing a computer peripheral.

    most excellent

  19. Daniel's Videos and Etc. says

    After watching this, It shows how inaccurate hollywood portrays these tape drives in movies.

  20. erikderuiter7 says

    Thank you so much for making all these wonderful video's!!

  21. Random Indian Dude says

    Damn there's a flippin clutch !

  22. RobM says

    beautiful !!! kids this was computing before facebook 🙂 I need a time machine.

  23. srinivasa murthy karumuru says

    The red shirted working hands look to be of same age as 1401, marvellous video..

  24. 2BTV Dave'sMusic says

    I wonder how many punch cards to read in a cat pic

  25. 2BTV Dave'sMusic says

    I've just found my favourite videos 😎

  26. Gary Hoffmann says

    Now the same can be done by a small section of one IC in your mobile phone.

  27. Keith Willis says

    Does anyone have any footage of the Storage Technology Corporation STC-3600 series drives? I worked with them in the late 70s (hanging off Gould SEL minis), and loved them a lot.

  28. Ray Rafferty says

    Are those gentlemen in red shirts former customer engineers? Imagine repairing these in the old days with your white shirt and tie on (required) to project the air of professionalism. Many white shirts were ruined and no expense reimbursements. IBM had boat loads of part numbers! Once an amazing place to work with a great group of amazing people!

  29. runner007 says

    Amazing expertise

  30. Rob Scovell says

    Those under-floor connectors!

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