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Suppose you wanted to take one of the 1977 trinity (Apple II, Commodore PET, TRS-80) and attach it to a hard disk at that time - in 1977.

Of course this wouldn't be easy. Not only was there no packaged solution, there was no hard disk controller designed to connect to any kind of microcomputer. Those came years later.

Still, suppose you were willing to take on the task anyway, design your own controller. What sort of hard disk could you buy on the market in 1977? Presumably something designed for a minicomputer? Was any hard disk available for separate purchase for, say, less than $5000?

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    @C32: I think you missed at that time. There was no IDE at that time, CF cards are way off, and the one standard for harddisks was SCSI. – dirkt Aug 16 '18 at 8:17
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    IEEE488 (aka HPIB) hard drives were available in 1977 as packaged devices. My first hard drive was a 5Mb IEEE488 device which I remember cost £7,000. – Chenmunka Aug 16 '18 at 9:32
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    Coincidentaly, $5,000 is exactly what my father paid for his Corvus hard drive for his Radio Shack Model II in 1980, I believe. A whopping 20 megabytes that he declared would "never run out of space." It used VCR cassettes to backup the data. It was huge and heavy. – Bill Hileman Aug 16 '18 at 17:23
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    Take a Shugart SA 400 floppy drive ($390 in 1977) and replace the eject mechanism with a second read mechanism using the same spindle and stepper motors. This would give you a 200KB "hard drive" for under $1,000. Switching to a miniaturized version of the platters in the IBM 3350 would give you a lot more storage but it might also drive up the price. – snips-n-snails Aug 16 '18 at 20:42
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    What Chenmunka said above. IEEE488 bus hard drives were already available at that time, and the PET even includes an IEEE488 port on it out of the box. This was a problem that was already solved in 1977, even if the solution was prohibitively expensive. – mnem Aug 16 '18 at 22:10
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First of all, it's rather frivolous to ask for a hard disk with a microcomputer in 1977. If one could afford a hard disk, one would buy it with a mini. And even then it would be rather an SMD drive.

The only hard drives (as in non-exchangeable, fixed closure) available in 1977 were the namesake Winchester drive (IBM 3340) and its direct follow up of 1975 (3350). A 3350 would cost you about 75,000 USD, offering ~630 MiB storage. So spending another 20 grand on a mini with controller might have been cheaper than building an interface to fit it to one of above micros - beside that, in 1977 even floppies where still considered optional on mini computers - and unavailable for either of the above micros.

In 1977 CDC's SMD drives were widely available, standardized and comparably cheap. A good example for 1977 would be buying the DEC RPJ04 bundle (RP04+RH11 Controller). This would offer 80 MB at 'just' 37,000 USD according to DEC's price list of 1977. Now your micro just needs to speak Unibus.

DEC is a good marker, as they tried to be the cheapo, at least until the late 70s. A RK01/03 was already available at less than 3000 USD ... but also only holding 1.6..2.5 MiB, so not really much past what a (cutting edge) floppy could offer at a similar price.

And then there was the RK05, and its compatibles. In 1977 a RK05 (alike) would be around 5-8 grand, including DEC compatible controller while offering a whopping 5 MB.

The biggest bang for the buck would be a CDC hawk drive with 10 MB for under 3,000 - plus another 2,000+ USD for a controller. Plus cartridges, of course.

Long story short, connecting a hard drive to a micro in 1977 wasn't anything even the weirdest of all geeks would dream of. Give it 2-4 more years and then we start talking.

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In 1981 I acquired an IBM 5444 from an old mainframe computer. Luckily I also got the service manual for it, and so was able to design a controller board to interface it to my Sinclair ZX81. The interface circuit only used about a half dozen TTL chips and was quite simple, but the ZX81's clock frequency was slightly too low so I had to disable the drive's bit rate lockout (just had to cut a track on one of the SLT logic boards).

At a data transfer rate of ~6uS per Byte it took less than 120ms to load or save the ZX81's entire 18kB RAM, and that was the extent of my 'file system'. Each 15" removable cartridge had ~2MB of storage capacity so it didn't matter that this method was somewhat wasteful.

While this setup worked well it was quite unwieldy. According to a warning label on the drive it weighed over 25kg, but it must have been a lot heavier than that because I almost put my back out trying to lift it. I also had to build a big power supply to produce the several voltages it required, including 24V at 6A.

I dumped the drive many years ago, but here is a picture of a similar one.

enter image description here

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There were SCSI cards for the Apple II, so you could attach a SCSI hard drive. Hard drives were also supported by ProDOS, with a volume size of up to 32M, and hierarchical subdirectories.

So, it was easy, there were packaged solutions, and no need to design your own controller. :-)

For the Commodore PET, there were also harddrives available, e.g. the D9060, which was attached via the standard IEEE 488 bus. This bus was not available on the C64 and VIC-20, which is why people made IEEE 488 expansion cards for them.

If I had to design a controller, I'd probably also opt for SCSI even though it was much more complex than IEEE 488, because you'd need to buy harddrives somewhere which to attach them to the controller.

Edit

If the question is mainly about what was possible in 1977: The ST-506 is from 1980, SCSI was made public in 1981, so I guess it would have been very difficult to find affordable harddrives in 1977.

Adapting, say, an IBM harddrive would have probably been cost prohibitive for the normal user of the "1977 trinity". If you had that kind of money, and if IBM would sell or lease you a harddrive in the first place, you probably already had an IBM mainframe somewhere.

A DEC harddrive like the RP04 (from 1975) would have been easier, but still quite expensive.

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    True, but weren't these invented some years later? I don't think any of this existed in 1977. (Edited question to clarify.) – rwallace Aug 16 '18 at 8:26
  • @rwallace Well, I guess the solutions that were actually implemented a few years later are the "design your own controller" solutions from before, so we actually know what people did back then ... – dirkt Aug 16 '18 at 8:29
  • Agreed, that is a guide to what the solution would look like. The thing I'm not sure about is what hard disks were available in 1977 to potentially attach to such a controller. – rwallace Aug 16 '18 at 8:32
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    SASI (later called SCSI) was first presented in 1979. Similar all Commodore etc. drives where later models. – Raffzahn Aug 16 '18 at 8:41
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I worked circa 1978 at a company that was interfacing an DEC RK05/IBM 2315 type cartridge hard disk mechanism to a custom minicomputer. They engineers in the next office were designing the interface boards. IIRC, The interface between the HD analog boards and and the computer memory bus was 2 boards, using TTL logic, that were each roughly 1.5 to 3 times the size of an Apple II motherboard. (Maybe Woz could have done it in less chips?)

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