Coleco ADAM 3.25 inch disk drive PROTOTYPE

ADAM 3.25 inch disk drive prototype

Many companies that produce toys, electronics, even automobiles, have many concepts, ideas and prototypes that never find their way to the marketplace.  Coleco is one of those companies.  They had many prototypes in their consumer electronics division.  One of which was a 3.25 inch disk drive.

ADAM 3.25 inch disk drive prototype

 I don’t know too much about it, but what I do know is that the one pictured is a WORKING prototype.  As for why they chose 3.25 inch disks instead of the more common 3.5 inch disks?  I was told that it was more cost-effective for the company.  Afterall, with the ADAM, you got a COMPLETE computer system for far less than the cost of a computer, printer, data drive from Commodore, Atari and Apple.  Coleco was always looking for a more affordable way to produce the hardware and to pass the savings onto the consumer.  Apparently, they could have acquired 3.25 inch disks and drives for much less than 3.5 inch versions.

ADAM 3.25 inch disk drive prototype

If you want to see more prototypes for the Coleco ADAM computer and it’s accessories, check out an earlier post of mine: ADAM computer concept art, prototypes and accessories.  I would like to thank Howard Eglowstein, senior software engineer for Coleco, for providing the photos and information.

ADAM 3.25 inch disk drive prototype

16 thoughts on “Coleco ADAM 3.25 inch disk drive PROTOTYPE

  1. Another tremendous update with some great pictures… Thanks! As far as why Coleco decided to go with the 3 1/4″ drive, I would venture a guess that they wanted to have control over the sales of the 3 1/4″ disks much the same way that they did with the Digital Data Packs and they could be more easily setup to format a 3 1/4″ disk to the same size of a DDP, 256K, without wasting as much space. The 3 1/2″ drives were just coming out at this time, so they would have been considerably more expensive and could you imagine the uproar from the masses of formatting 720K disks at 256K and wasting all that storage space.

    • I wouldn’t assume we had a crystal ball back then as we certainly did not. The decision was really pretty simple. We started with the wafer tapes (before I joined) and determined that these werent the answer. We engineered the tape drive (just as I joined) and a lot of it was custom stuff. The drive was made for us. The tape was digital, not analog tape, etc. You know all that crap. Once we decided we need a disk drive too, the 3.5″ was just becoming available and was wicked expensive. The 3.25″ seemed like it ought to be inherently cheaper so we decided to go that route. We got samples, built an interface for it and it worked fine. We eventually dropped it in favor of a 5.25″ drive because the IBM PC was clearly setting a standard and we could do that as cheaply as the 3″ option. I wasn’t involved in negotiating the drive deal, but I can believe that folks saw the swirl around the standard and decided not to get involved. This was right before the Mac came out and made the 3.5″ floppy the standard. Perhaps we knew that was coming and perhaps not. The 5.25″ was an obvious keeper and we opted for a cheaper single-sided drive to save money. Perhaps not the best idea.

      As for capacity, I think EOS allows up to 65534 blocks of 1K each, or 6MB. There was plenty of room for drives larger than 256K if we chose to make them. I picked the 160K format since it was either that or 180K. We had to make disks that were easy for outside vendor to duplicate. The 160K per side was an IBM standard and well supported by the industry. I don’t recall what the 3.25″ Dysan disks could hold, but if it was 720K (and that doesn’t sound familiar) then we would have supported them at full size. When I lost the battelt to get a 2-sided drive which would have made the drive 320K or 360K (depending), I settled on 160K because it was the easiest path to support at the time.

      Thanks for thinking that we could have controlled the 3.25″ market, but there were other companies courted with that drive. I think only one computer ever shipped it.

      • Actually, now that I think of it I believe that ADAMNet block devices used 4-byte addressing. If that’s the case, the maximum block number is 2^32-2, or 4,294,967,293 blocks of 1K each. That’s 4,398,046,508,032 bytes or nearly 4 TB. The largest device I ever tried as an ADAMNet device was a 5MB hard drive. Back in 1983, the mere concept of a terabyte of storage was incomprehensible. Now we have that much in pocket-sized hard drives.

  2. Thanks for the tremendous follow up, Howard. It’s always such a pleasure to hear from former Coleco employees who played such a large part in the development of our favorite computer system and the accessories designed for use with it.

    I never realized that the 5 1/4″ 160K FDD wasn’t the first choice and am glad that this was indeed the drive that was manufactured (even though a double-sided 320K or 360K would have been preferred now that we can look back on things) seeing as it would have been a little hard to find 3 1/4″ disks in the wild… especially now-a-days for us retro-computer enthusiasts.

    Over the years, I have heard numerous accounts of what an impressive system the ADAM actually was (ADAMnet was actually USB long before USB, 4TB drive capability, etc,) from other Coleco employees (Phil Kosowsky, David Hinds, etc.) and read interviews of Eric Bromley and Walter Banks, which makes it even more heart-breaking that things turned out like they did. But then again, if the ADAM did become a commercial success, the Users Group community that developed to support it would have been a vastly different animal.

    I would like to invite you to join the ColecoVision & ADAM Sub-Forum on AtariAge ( This is a very well supported and active forum and I know there are many members on there who would love to hear from you and to be able to discuss things with someone who was actually heavily involved with the decision making and development at Coleco. BTW, not trying to steal you away from Justin and posting further info. on here as well. : )

  3. In 1984, when the Mac introduced the 3.5″ drive, they were SSDD disks, and only had 400K on them.

    When Mac moved to DSDD disks, that’s when they held 800K. Of course, the IBM format gets only 720K on the same disk.

  4. These look like pictures of my drive. I can tell by the handwriting on the 3.5″ disk. I sent them to Howard several years ago. I think it is one of the few that were actually made.
    The 3.5 / 3.25 debate was not that strange. The 3.5 had not not taken hold yet. I remember a few years later that they were still expensive.

    • Joel, can you tell us more about this drive? The folks who read this blog are ADAM crazy, as am I 🙂

      I dunno, since Apple debuted the Macintosh in 1985 with the 3.5 inch drive, I figured it was a done deal by then.

    • Yes, that is in fact the Coleco prototype that Joel ended up with. The leftover wonders have certainly scattered far and wide. As far as I know, Coleco only had two samples of the drive and our model shop made one of them into that classy little mockup. I put an ADAMNet controller on it. Joel and the other wacky kids at Lazer were making sure that CP/M and BASIC worked with everything – I wasn’t surprised when it surfaced in Joel’s collection (I ended up with tape drives that could format tape and the only hard drive).

      The only company I know of that shipped machines with this 3.25″ drive was Seequa who shipped a version of their dual CP/M – MSDOS machine with the Dysan drive for a really short time.

      • I think Howard is correct. We probably had it at Lazer to make sure our products would work with it. By the time I left Lazer no one there cared about the Adam so I kept it.

        I don’t recall adding any extra features for it. Maybe we had a program or command to format the disks.

        I still have a few items left from those days. My notes about programming, a bumper sticker.

        I saw somewhere else on your site about a game you wrote. That was one of the first things I wrote when we had hardware to run our basic on. I used the boat character to move it around the screen using the joystick. I had noted that they had not filled in all the characters in their character set. So I took a book from the IBM PC and generated lots of strange characters. The boat was because my friend and co-worker and I were big windsurfers. It is actually a wind surfer not a boat.

  5. Quoting Howard, “tape drives that could format tape” sounds like the heavily modded Exp. Mod. #3 Tape Formatter that I was given by Doug Rosenvinge in 1992. Doug had acquired a large number of prototype items from a fromer Coleco employee which also included the 3 1/4″ disk drive prototype, 1200 baud ADAMnet Modem, SmartWRITER Rev. 81 and 84 proms, complete 2-disk version of Jeopardy, 2-disk version of Richard Scarry’s Best and some other odds and ends. The EM #3 Tape Formatter was a nifty little item that was a self-contained unit (no monitor or keyboard required) and was powered by a ColecoVision power transformer. All one had to do was place a tape in Data Drive #1 to make a Center Dir. DDP or Data Drive #2 for a Right Dir. DDP and after a short delay to start and a couple minutes later, you had an ADAM Data Pack that just needed to be INITialized. When I shut down the NIAD group, I gave this item to Lyle Marschand with the rest of the remnents of the group/mail order. What a terrible mistake on my part!

    Here’s the link to our newsletter PDFs with further details:

    Click to access niad%20095%20-%20aprmay%201993.pdf

    Click to access niad%20096%20-%20marapr%201994.pdf

  6. There have been a number of former Coleco employees that have contacted one of us Coleco fans over the years and most have seemed to be involved in R&D and programming out of the CT facilities. Some that come to mind are Bill Rose, Paul Jaquays as well as Howard. David Hinds (Supplier Quality Assurance Department) contacted me a couple years ago and sold me his entire CV&ADAM collection and Phil Kosowsky (testing and repair in the NY facility) is still in touch from time to time after many years in the ADAM community as a mail order vendor and repair service. Even Eric Bromley was interviewed by a popular retrogaming magazine a couple years ago and Leonard Greenberg showed up on,

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