A new addition to my workbench.
This is not a real IMSAI 8080, but a simulator with a full replica front panel. But it looks pretty convincing from the front, and a most impressive web interface.
The kit comes from a local Aussie
https://thehighnibble.com/imsai8080/ and is US$250 plus shipping.
I only received and built it last week. This was the first kit built other than by the creator.
The kit was really nicely packaged and came with all the parts. Just a few hours soldering and assembly required. Quite enjoyable.
There will be a video up on the MickMake channel soon - watch this space... or subscribe to his channel
Now the question is this a sort of simulator eg is the front pure cosmetical or can you really use it as an Imsai ?
Yes you can really use the front panel. Before I got the web interface running and set it to boot into CPM, I manually toggled in a couple of test programs from the original IMSAI manual via the front panel, and they worked as expected.
but , where is the s100 bus ?
but , where is the s100 bus ?
Do you have S100 cards you like to use?
but , where is the s100 bus ?
Thankfully not required 
but what about my nice io expanders , floppy controllers, drive controllers and other stuff ?
but , where is the s100 bus ?
Thankfully not required
but what about my nice io expanders , floppy controllers, drive controllers and other stuff ?
The IMSAI 8080 is noteworthy for being one of the very first microcomputers and its funky (from a 21st century viewpoint) toggle switch interface reminiscent of earlier and contemporary mini computers. So it does make some sense to replicate that (I suppose -- I'm not entirely sure about that
If you must (why?) use a S100 bus, there are other options:
http://www.s100computers.com/
Idk, as a hardware
purist pedant, I'd be more interested in an S100 bus clone system (S100 bus was /very/ basic, and iirc, just a standard way to link cards together, usually offering semi-standard ideas on where what connectors should do which and what.).
The visual accuracy is really neat, and it would potentially make a really good basis for creating your own replica IMSAI 8080, but I wouldn't buy it. This seems like it sits in a weird inbetween of simply using modern PC-based emulation software, and having an accurate clone. It might be neat for someone who just wants to play around with switches, but part of the joy of collecting computers for me is getting old (or replica) gear put together and working like it would have originally. Maybe it's because I'm a little squirt, but this gets me to understand what history was like from a computing perspective for systems before my time. If I just put together a fancy plastic panel, but don't have the real computer, it's eh.
That's just me, though, and I mostly wanted to make the guy complaining that this doesn't have an S100 bus not feel left out.
While this is a great 'visual' replica my gripe is more in the sense of : there is no i/o !
The whole purpose of these early homebuilt machines was to put parallel io , serial io in there and DO things with it.
there is no need for ram and rom cards as the emulating platform has plenty of space for that. But it would be nice to have a block of io.
at least bring out 8 address lines, 8 data lines , a read and write strobe and a chip select.
That's just me, though, and I mostly wanted to make the guy complaining that this doesn't have an S100 bus not feel left out.
It's not just you. And the guy complaining about the S100 bus left out has a point.
I am conflicted on this. For these 8-bitters which you could fairly easily build either an exact replica or your own design which worked the same as the original, as many of the required support chips are not yet unobtanium, I can see wanting to build a real machine and not an emulator with a replica front panel.
For other machines - well, I've love to fool around with a PDP-11 again, but I don't have the room for a whole rack of the REAL peripherals, and the most fun I had with one wasn't interacting with the computer's peripherals, but the even bigger machine it was controlling - and I CERTAINLY don't have the funds or room to set up something like that with all the support systems (electric and air) that would be needed. The one I used was an 11/T23 so there was no real front panel per se, but being able to connect a terminal emulator and running RSX/11 on it, with some SD card or what have you would be plenty nostalgic.
I do still have my first computer, another 8 bitter that I assembled from a kit. It has all the 'stuff', including a couple of S-100 slots, and a power supply big enough to populate them. It has a hex keypad and a bunch of status LEDs, plus hex displays for address and data, but I always did have the idea of making one that had a full front panel like an Altair or Imsai, even if I already had that information available in an easier to use interface - just because a face full of blinken lights looks cool.
While I agree this may not satisfy the purists, I am quite happy with owning this simplified replica as I think there is little chance of me acquiring a real IMSAI 8080. Plus the web interface makes it a little more fun to use.
I am the owner of quite a few other vintage computers, I think 6 various TRS-80's models, a stack of Microbees, several IBM RT & RS/6000's, Sun IPCs, a MicroProfessor, VIC-20, maybe an Apple II, and so forth. And several home built Z80 & 6502 machines.
BTW, this IMSAI replica does have two serial ports on the back, real RS232 as well, but I think only one is currently functional in firmware. And there is some expansion I/O available (another 4 bits in and 4 bits out I think) which the firmware could be made to control in its simulation. I'll also note that the front panel is I/O and provides 8-bit input and output ports you can use from an application.
While it doesn't look as neat as the IMSAI, Altair 8800 clones are I believe plentiful, replicating real S100 hardware.
As for the guy who wants a PDP-11, I'm a yougun, so PDP anything is /nowhere/ near my time. Regardless minicomputing is probably one of the most interesting segments of historical computing (yes grandpa, you're history now!
) I can think of, and is really where computing went from expensive and experimental, to truly being the every nook and cranny basis of our modern technological infrastructure. All of the modern computing systems we rely on daily, like Unix and C (which runs almost all of the world's computing through some derivative or another), originated on minicomputers, and the sheer utility that was achieved out of what was so humongous and simple is something I simply wish I could spend a handful of hours experiencing in the flesh. PDP-8 or PDP-11 being my first choices, particularly in the really neat 70's colourful cases, logos, and switches, (my sense of aesthetics is very strange indeed).
Getting a 70's micro or mini is on my bucket list of things to do, and I'd love an IMSAI 8080, as it's easily the coolest looking micro of the 1970's hobbyist computer scene (though you can't knock the PET).
For other machines - well, I've love to fool around with a PDP-11 again, but I don't have the room for a whole rack of the REAL peripherals [...]
That sounds like you should be getting the PiDP-11:
https://obsolescence.wixsite.com/obsolescence/pidp-11I have not built that one, but the earlier PiDP-8 by the same designer, Oscar Vermeulen. The concept is similar to the IMSAI replica (and I assume the IMSAI replica has taken some cues from it): The actual machine is simulated on a Raspberry Pi running SIMH, and Oscar has added a very nice 2/3 scale front panel. Again, no "real" peripherals, but Oscar has done a nice job integrating "tape drives" via USB. There is also an optional graphics display so you can run Spacewar!
https://obsolescence.wixsite.com/obsolescence/pidp-8
Kean, I remember a two byte memory clear program for 8080/Z80 - 0000: 33 C7 You might have to run it twice to clear all memory. I think it'd be a good test of the emulation.
In 1976 I assembled a MITS Altair in a weekend for school. Lots of fiddly stuff there - the Imsai's design was better. The Altair had an 8 wire cable from the CPU board to the front panel. I swapped the order of 4 wires so it didn't work as expected and it took a few hours to figure out. One really clever thing was how MITS and IMS added a front panel that allowed you to view and modify memory without a firmware monitor. It was done by jamming instructions on to the 8080 data bus thru the above cable to alter the Program Counter which provided the memory address and then held in wait. I think you could also examine I/O ports too. It would have been nice to see register contents like some of the PDP-11s.
A friend of mine bought both an Imsai and a ProcTech SOL new. We worked at the same company and he got to design and microprogram a bit slice processor for a product. He said he was thinking about bit slicing an 8080 processor for some real speed.
There's a thriving S100 Bus community, with new (!) S100 Bus boards coming out
all the time.
I'm currently building a system, and the most expensive components are the 100-pin PCB edge connectors. My system with an 8080 CPU board and a Z80 CPU board (so I can run my old CPM apps from the early 80's), with the front-panel display PCB will only cost around $300 for PCBs and parts I don't already have.
The thing about the Imsai that I used to like was the setup of the toggles for easy hex digit entry - until I discovered Intel designed the instruction set to better suit octal, which made the layout of the Altair actually better. All this because my first micro was the RCA 1802, which has the instruction set neatly arranged for hex opcode. Heath H8 also set up the front panel to suit the Intel octal opcodes. I don't know why I have such trouble with it - I guess because I learned hex first and octal seems so clunky because it's LESS than decimal. But for whatever reason I really dislike things being in octal. Maybe it's OCD, because the bits don't line up neatly for multiples of 8 bit bus widths.
A friend of mine bought both an Imsai and a ProcTech SOL new. We worked at the same company and he got to design and microprogram a bit slice processor for a product. He said he was thinking about bit slicing an 8080 processor for some real speed.
Signetics actually did that:
https://archive.org/details/bitsavers_signeticsSrManualMar77_5343735
The thing about the Imsai that I used to like was the setup of the toggles for easy hex digit entry - until I discovered Intel designed the instruction set to better suit octal, which made the layout of the Altair actually better. All this because my first micro was the RCA 1802, which has the instruction set neatly arranged for hex opcode. Heath H8 also set up the front panel to suit the Intel octal opcodes. I don't know why I have such trouble with it - I guess because I learned hex first and octal seems so clunky because it's LESS than decimal. But for whatever reason I really dislike things being in octal. Maybe it's OCD, because the bits don't line up neatly for multiples of 8 bit bus widths.
I'm an old relic from the 70s mini-computer field service era (Varian Data Machines). I also really disliked octal notation after being exposed to HEX notation. The problem was that if two packed ASCII characters are in 16 bit word, there is an extra mental hoop jump to unpack the one shared octal character containing value from both the high and low ASCII characters, while in hex the two characters are just split at the byte boundary.
It's kind of funny. Those hobby computers are really the last designs to have blinkin' lights. And for the most part they had them because all of us poor hobby folks who wanted our own computer wanted a "real" computer like the IBM and Burroughs and DEC machines we really wanted to have but couldn't afford, and they all had blinkin' lights.
Once I/O moved off of punched cards and teletype machines the blinkin lights really didn't make any sense and departed from the commercial world and a decade or so later, from the hobby world.
The lights are handy for a very basic setup though. Up until home computers like the Apple II a monitor or teletype was a real luxury.
The lights are handy for a very basic setup though. Up until home computers like the Apple II a monitor or teletype was a real luxury.
I think we said the same thing in different ways. Sometimes it is hard to remember how much cheap silicon has changed things. It isn't just MIPS in the CPU.
A friend of mine worked in Burroughs. According to him when they dropped the lights their customers complained. So they were added back as an optional extra to the next version!