You aren't building a museum, you're building a MONUMENT to digital computing's actual history. I'm learning a lot, I've been watching since the Centurion projects started, and I'm in for the adventure! You're also doing a phenomenal job of telling the stories. Please archive every video you've made. Your work and results at this time in history need to be preserved.

Brings back memories... I wrote my first computer program (1967) for an 40-bit machine with 5 kilobytes of core memory and a drum holding 60 kilobytes including swap area for the core, a small OS, an Algol compiler and a few extras. Files were on paper tape and I still have a few tapes in my belongings. The computer was called "Gier" and the danish company RC built several hundreds of them as far as I can remember.

The Librascope LGP-30 of the late 1950s was also a bit-serial machine. It was designed for scientific applications, and had a 31-bit data length and 15-bit instruction length. It had only 16 instructions but it implemented single-instruction multiply. Its bit-serial nature allowed it to be an exceptionally compact machine for the time. It had 4096 words of drum memory and three general purpose registers which were also on the drum. There is one fully working machine at the University of Stuttgart.

OMG the IC's dated my week of birth! Never have I expected to see the production ICs this old! In the autumn of my life, I dare to say it was a very good time to live in.

I LOVE those 60s/70s (?) carbon resistors... they remind me of my childhood salvaged components collection. A lot of it looks far more modern than I was expecting: ICs and flexible PCB cables, etc.

It is interesting how weird stuff persisted into the 1970s. This Litton machine is pretty epic with drum storage rotated by a Bodine motor which would have been at home in the 1930s. I worked for a bank in the proof and transit operation supporting 32 IBM 1260 electronic inscriber machines. The 1260s were full of boards of SLT, used plugboards for setting up the routing program and stored their totals on a acoustic delay line memory. The delay line was a bit like an unwound clock mainspring in about a 12 inch x 12 inch box. Information was stored by an electromagnet torquing one end of the spring, making pulses travel to a pickup at the other end. The picked up pulses were amplified and put back into the spring. As you might guess, environmental vibration such as a cart full of checks to be inscribed bumping into a machine caused angry operators who had to reprocess lost work.

Fascinating. I know virtually nothing about this era of computing but it's slowly coming to light due to your videos. Thanks!

Ever since I watched the movie "Flight of the intruder" I was fascinated by a scene where the bombardier had to "kick the computer to get it going again.", which was a computer that he used for bombing targets with the A6-Intruder. Low and behold, Litton made that computer that went into the real-life A6-Intruder bomber aircraft. In fact, im willing to bet you have either a close relative of that computer or a copy of the guts of it, timeframe matches. So the reference in the movie is a real life reference to kicking the drum on this computer if it got stuck. Incredible.

My god, drum memory! I never thought i would see a computer of that type again, let alone possibly operating! Great score, Usagi. The link between the Litton and the Centurion seriously makes me smile. Your enthusiasm is so contagious I am always grinning ear to ear watching these videos. Cannot WAIT for you to get the beast running and the tape reader going!

11:12 So cool to see a Bodine Electric motor - my great grandma worked there! When I was little, she used to tell stories about winding motors and even gave me some broken motors to take apart, to see how they worked.

The front panel is beautiful. Looks like it was designed by Braun. And the Microgramma font is *chef's kiss*

Paper tape is very hacker friendly in that it's very easy to build a reader these days. Jürgen Müller has designed a reader based on an Arduino Pro Micro that looks very easy to replicate and use. A punch would probably also not be too difficult, but definitely takes the amount of work up a notch.

Wow, how cool! It sure does look like a washing machine, too, lol. Litton made my family's first microwave oven, and it was a sturdy, long-lasting 1970's beast of a machine. Every time one of our newer microwave ovens has failed, we miss the Litton. We only replaced it because the door latch broke, and replacement parts were no longer available. Alas! Hopefully, your Litton minicomputer will be just as sturdy and reliable! 🙂 Those de-laminating cables look scary for sure, but I would hope that you'd be able to repair any failed connections with sturdier ribbon cables. 🤞

It's been a while since I ran any BSD Unix variants, but I remember the swap device was named /dev/drum.

Beware: before starting the drum, ensure that the machine is very well secured to the floor, and check the lubrication.

I had a complete working Litton ABS system as shown in the video: CPU, paper tape punch/reader and printing terminal. It used large circular military connectors for interconnection. The terminal had an interesting keyboard which had an interlock mechanism that only allowed you to press one key at a time (all other keys were mechanically locked out and you couldn't press them). It was a rather slow and noisy affair. At the time I was a poor typist, and I could still out-pace the keyboard mechanism. The whole system ran an operating system called OPUS (if I recall correctly). The drum was remarkably quite, although the paper tape punch was very noisy. Someone added a power switch to turn off the punch motor, but it would create a power glitch and crash the CPU every time. The paper tape reader was all mechanical: it had little pins which poked through the holes in the tape. Using a cam, all the pins were withdrawn and the tape would advance one sprocket. The pins were then raised to detect holes in the tape. The PCB's for the tape reader/punch were very large (maybe 20" x 12"), with only transistors, diodes, resistors and capacitors - very sparsely spread out. Sadly, I threw out the Litton, along with an NCR 299 and a Data General MV8000 (yes, the model which was written about in "The Soul of a New Machine"), and yes, I'm regretting it almost every day....

That 0.100" flex cable was popular in several machines back then. I have a few HP frequency generators that use it. If you come up with a way to replicate or replace it, let me know. The only thing I could think of was an adapter PCB to convert them to "normal" IDC headers and ribbon cable.. even that tech is vintage now. On the plus side, you get that drum memory spinning up and that cabinet is never gonna tip over.. as the memory turns into a massive gyro :) Cheers,

I kind of remember seeing a couple of these back in the early days of my Vo-tech training for machine shop. There was also a 'data processing lab' which is what they called the computer room at that time, and when I first started at the Vo-tech in 1972, they actually had a couple of these Litton machines. They later switch to DEC and PDP as they had better support. The only other Litton products I was familiar with were microwave ovens, which were starting to get popular in American homes at the time. It will be interesting to see if you can get this relic up and running 50 years later!😉 *EDIT:* Just a side note: In our machine shop, we had one of the first digitally controlled vertical milling machines ever released. It also used punch tape to operate, and we would spend hours on an old punch tape TTY creating the programming to control the x,y, and z parameters to mill various projects. It was before automated tool change cassettes were popular, so we had to program pauses to allow for tool changes and then hit a button to allow the tape to continue.

Balancing this upload with VCF prep is amazing. Can't believe that I managed to speak to you at the fest and then come back home to have another full-length upload waiting! If only there were a way to get drum memory nowadays without harvesting it from an existing computer - or, at least, harvest it from one beyond saving. That'd be so perfect for the Vacuum tube computer

Drum memory! Now I get to retell a tale I read a long while ago (although I'll have to shorten it considerably for the comment and also because I don't remember some of the mundane details). This was in the days of the Real Programmer. This particular Real Programmer worked with several other people, one of whom told this tale. To set the scene, the Real Programmer was so good that he knew exactly how fast the drum would spin and also exactly how long it would take for each instruction to execute, and so in order to speed up his programs, he'd tell the assembler exactly where on the drum to put each instruction. He timed things perfectly so that just as one instruction finished and the CPU began looking for the next instruction, it was just about to pass underneath the read/write head. When there was a printer which required a short pause between each character, instead of programming a delay loop, the Real Programmer repositioned the instructions in the print routine so that when each instruction had finished, the next instruction had just passed under the read/write head and so the CPU had to wait for the instruction to come around again. Due to some events which I forget, the Real Programmer knew he was going to be fired, but he left a legacy. In a program which printed a report, he programmed it to occasionally print a random asterisk, thus spoiling the formatted output. It didn't ruin the results since they could still be read. It was just annoying. The person reporting the story was told to try to find where the code was which produced the asterisk and remove it, so he started trying to trace the program flow. To his astonishment, he reached a point where the instructions reached the end of the drum but it very obviously wasn't the end of the program. After puzzling over it for quite a while, he eventually figured out what was going on. What does a binary address counter do when it reaches the highest possible number and then you add one to it? He went to the start of the drum and sure enough, there was the next instruction in the program. So impressed was he with the Real Programmer's skill and cunning that he stopped looking and just told management that he couldn't find the code which was inserting the asterisk. After all, how were they going to prove otherwise?

By the looks of those boards, that Litton may be a transistorized version of a design that used to be a tube computer.

All these collections of obsolete old things are what we need, lest we forget how we got to where we are. Like the Sony Triniton collector guy making a Trinitron museum. Love living in a society that allows these things to take place. Love it!!!!

Very cool - I have never laid eyes on a magnetic drum memory. I was told by fellow employees at GE in 1983 that previous versions of our E2C Hawkeye radar used MDM, but that is the only reference to it I have ever come across. I visited a friend in Colorado around 1988, and he told of ex-Litton computer company employees I believe. I think they had a location there.

I've heard about drum memory but have never seen it working before. I look forward to the future videos on this!

*YES, DIGITALLY PRESERVE THE PAPER TAPE WITH THE CENTURION!* This channel is so cool!

Drum memory! It's always fascinating too see how the old electro-mech stuff is implemented and the hoops the designers had to go through to sync memory access with execution. Mercury delay lines would be another one to see but obviously having tubes of mercury floating around isn't something you want to deal with these days.

No surprise it has a drum, it looks like a washing machine. Thank you for saving these pieces of computing history.

Old computers and old foreign cars. Your shop looks like my heaven. The Litton is insane! Congrats.

For the flex ribbon cables used on the bus that are falling apart I would use kapton tape and ever so carefully wrap them up. Also replace the electrolytic caps before powering up and check the bearings on the drum motor.

I think PCB Way can make the ribbon interconnects if you need to replace them. They are essentially just flexible PCBs with straight traces.

ooohhh I love the style of this machine.

I love that you are digging into MiniComputers!! They were the first systems I worked on. That I see an overlooked era of hardware. Thanks!

I repair avionics and a few devices I repair use those laminated ribbon strips to connect boards. I fix them by just brushing superglue all over the de-laminated plastic part before pressing them back together and it seems to work well to hold it all together

The one-bit CPU machines, your favorite!

That's an amazing story!! A piece of computer history I would never have learned about without your channel! Looking forward to seeing this machine brought back to life.🙂

Man I can't wait to see some running drum memory, only ever seen pictures. At that speed, probably hear it too! Looking forward to seeing you dig into it and show us more.

That is so cool. My Dad had a Litton in the early 1970 at his accounting firm, 5mb of storage, paper output and paper tape for storage.

I remember reading some old usenet anecdote about a guy who had to work with/on a machine with drum storage/memory which had an infinite loop set up in it's programming, and which confused the hell out of the young tech. After much research they figured out that the program which used the infinite loop managed to make it not so infinite because of the way the read head of the drum mechanism had to physically move, and even though there was no code way it could break the loop, there was something that made it seek long enough to land somewhere "wrong" that got it out of the loop and jump it somewhere is in the program.

Wow! What a find! I had heard of drum memory at my training at Nixdorf Computers. Apparently Nixdorf also had invested in drum memory. However, the manufacturing tolerances were very challenging and IBM had developed the disk drives. Interestingly enough the tracks on the platters are called cylinders to this day and that was according to our trainer based on the drum drives which had several concentric drums, or cylinders. Unfortunately, by the mid 1980s these drum drives were phased out in favour of the CDC drives. So I had only heard of them, but never seen one. About the ribbon cables delaminating. They look like simple straight through connectors. You should be able to design PCBs like that and get them made by JLCPCB, like the utube channel who shows all the PCB motors, I forgot the name. That should allow you to get a stack of them and replace what needs it.

I saw David at ECF East yesterday and I can report that he is very tall.

Wow, when I saw the thumbnail I though: Oh, was he getting bored with the Centurion and where did he come up with this one? 😂 As it turns out, they a computer relatives. Didn't see that one coming! You keep to amaze! Thanks for all the work you do!

I was at Georgia Tech as the institute itself and the school of computer science each changed computers. When I first enrolled there, the main computer for the institute as a whole was a Univac 1108. And it had no disk at all, only drum storage and tapes.

So, just when I thought you had mastered the craft...you go and UP THE GAME! Yet ANOTHER Forgotten Machine rescued, restored and extremely well-documented by Usagi! I salute you, and I am truly humbled by your accomplishments!

That is so cool, restoring the hardware and the fascinating history of how one system lead to another.

Great tie in between the Centurion and the vacuum tube computer. I remember someone suggesting mag. drum storage and you saying something like "where the hell am I going to get a mag. drum from?"... well, hello there!

Reminds me of The Story of Mel, a programmer of a drum machine.

Back in the late sixties I was a Physics student, and had access to a "Stantec Zebra" computer which also used a rotating drum as its RAM. It used a drum which stored 8k of 33 bit words (I just looked that up) and was the only machine I have come across which kept a teleprinter - not teletype - waiting for the next digit when printing a decimal number. It was huge compared to your Litton.

Ohey, my dad used to work at Litton (though the military tech division), and then at Northrup Grumman after!

I had one of these computers in running condition in +- 1980. really interesting to program. I ended up dismantling it for parts, and used the drum memory unit as a tactile/auditory effect in a 2 seat spaceship simulator i built- fully enclosed with a sliding top. i removed the rubber shock mounts on the drum unit and bolted it directly to the frame of the simulator. truly awesome sound and physical effect- sounded and felt just like a jet engine. ahhhh, nostalgia. I later built another simulator that moved in 3 axes using the panels from a discarded IBM 1401.

In the first 2.5 mins of the intro, I was convinced that there was a bed in the garage background. I was thinking “oho, Mrs Usagi’s patience has finally broken with the arrival of another mini computer and Mr Usagi is now sleeping in the garage!” Luckily, we pan out and see it’s just a cover on the car! Phew! 😅

This channel just gets better and better 😁👋😊😊

Prehistoric computing! Converting the paper tapes back to digital and viewing it on modern computers is a whole new level of data preservation.

When you opened up the card cage it looked like on of those frames that contained pop posters in music shops. As a kid you always fretted that they would overturn on top of you as you pulled each poster over to view the next. It is always fascinating to see how few components were used in those old machines, on boards the size of a pool table😊

If at the very least the drum memory works, you have a storage option for your own vacuum tube computer. You might even use the entire Litten machine as a serial storage device for it.

I love your TI-99/4a setup on the shelf. I still have my TI that I bought in 1983, which has several of the expansion components, including the PEB. Saving old computer systems is so cool.

When you said "Litton" all I can think of is the "Pink Panther". Well either that or a prize package on "The NEW Let's Make a Deal!"

wow, this is so cool, seeing a company be created to support hardware from a company that stopped making and giving support for their hardware is so wild, and then ending up making their own system with backwards compatibility for that system? just wow, basically this machine existing not only allowed centurion to exist but also made their systems use a very weird filesystem all to add backwards compatibility, this is so fascinating omg cant wait to see more of this, also, spinning ram? it looks like a very fast hard drive does it also keep data after its been powered down? does it have data rn? wild stuff omg. Also backing up those paper rolls into the hawk drive sounds really cool like digitizing it, its so cool to see how tech advanced so fast in the 70s and 80s

Can’t wait to see the drum working. You might be able to build a simple optical reader for the paper tape. Punching is a much harder problem.

A new man. You rolled 20 years back with that shave😮🎉

the Centurion family is unstoppable!!!! \o/

The cool thing is the rotating drum memory. The only other place that I've heard it used was the A6 Intruder's on-board computer during the Vietnam war.

You have such amazing luck finding this old equipment. I'm glad you do, since we all get to see it. Thanks for sharing all that you do.

Cannot wait to see where this adventure get us! Amazing work!!

Last time I saw a drum memory was in high school about 1975 . I was in an electronics course and we got old computers donated to us from oil company seismic outfits, the drums were used to record seismic vibrations from dynamite charges set off to find oil formations underground. These things were very heavy with fixed recording heads and pretty slow rotation as I remember . Looks like you found a real winner it Will be amazing if you get it to work again 👍

This seems a lot like the LGP-30 from about 1959 which was a deep-freezer sized tube and semiconductor diode "general purpose computer" that had a 4K word drum memory. It operated bit-serial, with 32 bits per word (though one bit was apparently a "spacer" bit and wasn't writable). It's teletype was a Friden Flexowriter and also had a separate paper tape punch and reader. The LGP-30 had a hardware multiply, though it took like 120 clock cycles to perform. The accumulator was stored as a track on the drum as well, and it's front panel had a small oscilloscope which displayed a square wave trace of the contents of the accumulator and IIRC the program counter. One thing I recall about the LGP-30's drum memory is that after spinning down the drum you needed to wait 1/2 hour before spinning it up again. This was because the drum would heat up and expand, and if you restarted it too soon the heads would hit the drum and damage it. There was a big homemade sign taped to the one I worked with that admonished operators to be sure to wait sufficient time for the drum to cool off before restarting-- apparently, head crashes were common and it could require re-positioning and/or replacing heads so that the new position was over an otherwise unused portion of the drum-- not a job you wanted to have to have done...

Wow, I thought my brother and I had some old computers, but that thing is older than anything we've got in our collection by like a decade and a half! That's impressive, even moreso that you got it working.

Fascinating. I know virtually nothing about washing machines, but.. wait. That is not an washing machine? You stole my words.

If it's 1971 you will probably find that what you think are transistors are early ic's with negative logic . I have early calculators with those and they take a lot of thinking to understand what is going on . I am excited to be on the journey with you In your KZfaq. Cool and very exciting!!!

Those boards are a thing of beauty. What a wonderful machine! You find the greatest gear.

I love this machine and the story attached to it! I'm so excited to see what the future holds for it!

Well this looks like it's going to be a very interesting project! Also, unrelated, but I loved the choice of music for the cleaning montage. It reminds me of the french duo Air.

Here we go again, Can't wait to see how this unfolds. Huge honor getting to meet you and talk a while at VCF East today, and getting sworn at in Japanese and Yiddish. I wonder if they ever got a sign of life out of that drowned classic Mac. Thanks David, keep the hits coming!

An absolute amazing find! I wasn’t aware of the link between it and Centurion, in business or the sector sizing. Just WOW!!!

Wow... so exciting to see the Litton at work !!

Your channel never ceases to keep me amazed and feeling nostalgic. I remember in my shop on the aircraft carrier. The bench that calibrated the inertial navigation unit for the A-7 was manufactured by Singer (yes the sewing machine people). At some point Litton had purchased or taken over that Singer division. The actual Litton bench that maintained the rest of the navigation systems for the rest of the now retired aircraft, is where I saw my first multi platter Hawk drive. It also had a single fixed and removable platter Hawk drive like yours. When you mentioned that the Litton looks like a washing machine. That made me laugh, because it wouldn’t surprise me if there was a Litton link to the washing machine industry somewhere. When we were at our shore duty station. Our Litton tech rep would get calls forwarded to him from unhappy Litton Microwave oven owners quite often. We had a lot of fun with that.

Although I know almost nothing about these types of machines it is so much fun to hear you talk so enthusiastically about them. I have watched every Centurion epsiode so far, so having yet another piece of the background was really interesting. Looking forward to follow your journey on this Litton minicomputer as you restore it to the same perfect condition as the Centurion! That should add another couple of years of superb content. ;-)

That drum really precesses if you try to move it when it is running. I demolished an incomplete one of these back in the early 1980s. I still have the drum itself, and the motor, which has been repurposed to drive my hobby milling machine.

Very cool. Amazing how things were in the realm of old computers. The history is very intriguing. Thanks for sharing it with us.

Great to see you, albeit briefly, at VCF East on Saturday. Good luck with this; you sure have more patient dedication than I do - lol.

I think the 40bit word length came from the Zuse machines. The Z22/Z23 used 40bit memory with and eight bit tape reader/writer, drum memory in addition to core memory. The Litton looks like a "economy" version of a Z22/Z23 to me. Would be interesting to see the connection there.

Holy heck, the Rhodes in that time lapse music is sooo good.

The question is, did they do any money laundering with it? Beautiful machine. The flex PCB ribbons really surprised me! You may try gluing the layers with some flexible polymer glue (no cyanoacrylate as it'll go brittle as the joint is bent). Fortunately you can design new flex (or rigid-flex) PCBs from JLCPCB or PCBWay, and while not original, they will be better quality :) "Miniature nuclear reactor" would be a good name for it, and the Centurion backstory is very interesting too! So bloody awesome that you got it :).

It is a crazy turn of events, but so exciting to follow. Thanks a lot.

Cool history lesson. :) I can't wait to see the tear-down and repair.

I luv your videos and always look forward to seing more and learning more about such vintage technology, i also like your furry friends :) The Centurion videos have been really cool too..

You get all the amazing things! That Litton amazing. It does look like a washing machine! Can hardly wait to hear what the drum memory unit sounds like! Thanks for the history lesson, as well.

Many of the PCB manufactures (like PCBWay and JLCPCB) offer FlexPCB now. So it should be possible to make new ribbon cables

Another machine that I normally wouldn’t be interested in, but because of your passion and storytelling, I’m totally hooked! (Nice meeting you at VCF East!)

I am also very curious about the result. They were great times when they came on the market. I am following you closely as I want to see this working, good luck, thumbs up!

I was working with a massive dual PDP 10 system that had it’s hard disks replaced by Drum Storage back in the late 70’s. it’s memory was magnetic core.

WOW....A Litton 1241 ABS Controller Unit. The first program I ever wrote was on this machine. If I recall, the paper tape is encoded as 7 bit ASCII with an extra bit for parity. You should be able to clock the old tapes through an optical array to read them. I remember that the Litton programming language could pretty much be likened to a subset of Assembly language. I was about 15 yo when my mother bought a used one for her accounting practice in or about 1976. It cost around $18k, which was a huge amount of money back then. I hope you find a paper tape reader/punch and teletype. Thanks for the memory.

This is awesome. For the papertape, maybe CuriousMarc can hint a help.

Computer history is so much more interesting than I thought. We're in "the future" where we can put 3-7 billion or more transistors in one CPU, but only thousands back then. They had conventions back in the 60's about the future of computing and AI, which kinda matches up to what we're living today with AI generated art, machine learning, quantum computing, etc. It's kinda cool how far we've come, and the potential for what's to come.

I like it. Great video - that's for sharing this awesome piece of history!

Push comes to shove PCBway does flex PCBs but i do belive you'll find something off the shelf.

DEC produced a lower cost version of its 12 bit PDP-8 minicomputer with serial ALU, the PDP-8/S. Drum memory was famous in the IBM 650, which served as IBMs entry level computer for many years in the Fifties and Sixties. Drums were used later for fast random access storage. One Burroughs drum weighed literally a ton and tendended to break free and walk around due the forces generated by its fast spinning drum. The Army and Navy tried to use the Burroughs drum in mobile applications but the the rotational forces were too much for the ship or truck carrying the drum.. The drum in this machine is a relatively minaturized version of the breed. Drum memory machines had to account for drum rotation when placing instructions. The techniques for optimium drum computer performances are similar to those used with RISC machines. Dead space in the instruction stream can be filled in by unrelated secondary operations.

thank you for saving these examples for the future.

Very interesting story between those two brands of minicomputers!

Whelp, I missed you on Sunday, I was beet from the walking around on Saturday, but you Guys/Girls were on stage, and all had to zoom out at the End, Hope the 60's RCA IC made it home with you, it a Pre Production A Version, Just Try and Find some Info.. I wanted to come back Sunday, MY the HVAC unit took a crap on me on Saturday, And Sunday was House Repaire weekend YAY..

I’m so excited about this new addition and I haven’t even a clue what you are talking about half the time hahaha but it’s does kinda make sense too