This is how to use an 8" disk drive on the PC

hello everyone and welcome back to adrian's digital basement on today's video i'm going to be working on the trs-80 model 2 again specifically the 8-inch disk drive that was in that machine i want to test it out and i want to see if i can make a floppy disk so when i get that machine working i can actually boot into the os and see if i can use that computer so without further ado let's get right to it [Music] so this is the actual drive that came out of the trcd model 2. as i've mentioned in previous videos it's a sugart model number 800-2 as far as i'm aware in non-ibm equipment this is a relatively common model i still have this lower mounting bracket attached to the drive because it doesn't interfere with the servicing of the disk drive and of course this is what angles the disk drive to the correct angle for the case opening on the front i think before trying to get this drive working let's dig into the actual history of the floppy drive and specifically the 8 inch floppy drive first so we can better understand what i'm going to be trying to do here in this video let's first start over here on wikipedia and it's the article on the floppy drive itself or rather the floppy disk the article states that after development of disks in the late 60s it was 1971 where the first commercial floppy disk was released and then soon after other companies joined on the bandwagon the disks and associated drives were produced and improved upon by ibm but also other companies like memorex and specifically sugar associates which is this drive we have right here this is made by sugar associates but it definitely seems that ibm's eight inch disc or the type one disc at was sort of the industry standard in the 70s it was in 1976 that sugar associates introduced the very first five and a quarter inch floppy disk drive the sa-400 and here's a picture of it i think anyone who's ever used an old retro computer from the 70s or into the 80s is very familiar with this drive now the funny thing is many companies made clones of this disk drives and with slight improvements and while those clones look the same on the front internally they were a little bit different than the sugart first disk drive this is the service manual for the sa-400 and it's an incredibly detailed document that explains exactly how the disk drive works to a very comprehensive level and allows you to fully service any of these original sa-400 drives that you may come across it was steve wozniak who ended up buying the sa-400 mechanism from sugar minus the electronics board and coming up with a new analog controller that went with it that would actually make it work with the apple ii and be so much less expensive than the original sa-400 mechanisms that were used on other competing computers sugar called the mechanism on these drives if i recall the sa-390 and there's a little bit of lore that sugar actually sold sort of bad mechanisms to steve wozniak for development and he was able to still make those work with his uh clever engineering of the electronics anyways like i mentioned by 78 it says here there were i guess 10 manufacturers making disk drives that were sort of clones of the original sugar five and a quarter inch and it didn't take very long for the five and a quarter inch format to displace the then common in the 70s 8-inch format that ibm was basically pushing with all of their machines and other machines like the imsa 8088 and altar typically would have eight inch disk drives as well i won't get into too much more history but obviously five and a quarter shift drive lasted for quite a while but eventually was replaced with things like the uh three and a half inch floppy drive that was made by sony and there were some other competing formats that had less traction and eventually went away now going back to the difference between eight inch and five and a quarter inch discs the obvious being the size is different the discs are otherwise relatively similar they're constructed in a very similar fashion where there's a felt material on the inside and a magnetic disc that spins and there's a floppy flexible case on the outside the big allure of eight inch discs was that they could hold quite a bit more than the contemporary five and a quarter inch discs and that's kind of the reason why i'm assuming that radio shack tandy radioshack ended up using this larger mechanism for the model two versus five and a quarter inch discs because at the time of the release of the model two absolutely five and a quarter inch drives were available but i guess that these larger drives were just considered the more professional option as that is what ibm was pushing with all of their professional level machines but also the capacity was greater on these in the late 70s when the model 2 was released it was pretty typical that five and a quarter inch and eight inch disk stripes were single sided meaning there was only one reed head and it's on the bottom side of the disk what you see right here on the top is simply a pad that pushes down on the magnetic surface so that it contacts the read head properly these eight inch drives spun the disc faster at 360 rpm and also had 80 tracks versus the more common 35 or maybe 40 tracks on five and a quarter inch discs giving you a substantial increase in capacity there are probably people that have a bit more familiarity than i do but i think at the time as well it was considered that these drives were a bit more reliable and the discs that went with them than the five and a quarter inch floppies as well back on wikipedia here there's a little table showing the capacity of these different disk drives and all of these are going to be eight inch drives right here so 1973 the sugar 901 could hold what it looks like about kilobytes and that was a single sided single density disk meaning that it was using fm encoding versus mfm encoding on an 80 track disk when sugar released the sa-400 it would have been using a single-sided single density or fm encoding for a marketed capacity of 110 kilobyte or a formatted capacity of 87k the apple ii using the exact same mechanism and some neat tricky encoding actually increased that up to well i thought 140k but maybe the formatted capacity is actually 113 kilobytes this table here specifically missing the sa-800 dash that we're going to be working on today but from my understanding it of course fully supports mfm encoding so double density but unlike this one here which says double-sided double density it's going to be single-sided and double density i just realized i've been talking about this disk drive without showing a comparison to how big it is and heavy it is compared to the five and a quarter inch disk drive this is a five and a quarter inch disk drive and if i hold it up to the eight inch drive you can see right there how much smaller it is now this is a half size one but of course a full height drive would be the same size this way it's just going to be twice as tall but you can see compared to the eight inch drive the massive shrinkage that has occurred from uh this one to this and you can be assured that from a weight perspective this thing is built it's so solidly it's just hard to describe how ridiculously over built and heavy this thing is now let me turn the 8 inch disk drive around so we can look at the drive electronics one of the things i want to do with this disk drive is i want to test this out on a pc and that's of course for two reasons the model 2 is not yet working i haven't managed to get that computer to power on yet while i haven't even attempted it and number two i have some good tools on the pc for testing out disk drives now you're going to say well there was never an ibm pc that used an 8 inch disk drive and you'd be absolutely correct and if we look at the interface connector here for the sugar drive it's this edge connector that's relatively big and if i hold the five and a quarter inch drive up to it you'll notice there's a difference in the number of contacts on this edge connector meaning that it seems like there's not going to be a way to hook this drive up to a pc because it doesn't have the normal 34 pin cable like a five and a quarter inch or a three and a half inch drive does and yes this is indeed actually a 50 pin connector but the thing is sugar when they designed this disk drive well they didn't design this exact one because this is not one of theirs but when they designed their five and a quarter dish drive that everyone copied everyone copied the interface protocol for that drive for all of these other disk drives and that includes three and a half inch drives they use a pin connector here but it's still using the same sugar sa-400 type signaling that that very first five and a quarter inch disk drive used well it turns out that when sugar made this sa-800 which i'm not sure if this came after the 400 or before it i think it came after it or around the same time that they used exactly the same signaling on this disk drive as the regular sa-400 uses what that means is that if we can adapt this connector to a pc cable and a pc interface card we should be able to control this disk drive without any problem there's also going to be a couple other things that kind of make it harder to use the eight inch drive on a pc versus the five and a quarter inch and it comes down to power one major thing about the eight inch drive that is so different than every other floppy drive or any computer peripheral you've ever used is that the motor that turns the disc that turns the spindle which on the five and a quarter inch disk drive is this thing on this direct drive model and on older uh full height models there's a little motor in the corner with a drive belt that is this thing right here this is the motor that turns the spindle but if i flip the drive over take a look at the specs on this 7.5 watts 115 volts and it's also 1500 1800 rpm the difference there is that this is what i think an induction motor i'm always messing up the terminology but that is 1500 rpm at 50 hertz or 1800 rpm at 60 hertz yes this drive motor it's powered by line voltage and that means when you turn on the machine that's using this disk drive like say the model 2 this drive just runs all the time now if i flip the drive around onto its bottom here this is the spindle that actually turns the disc and there is a drive belt right here that goes around under the pcb here to that large ac motor and this whole thing is turning all the time well if you've ever worked on ac motors like on your air handler in your furnace for instance motors like this require a run capacitor and that is right here and it looks very much like a run capacitor on your air conditioner in fact it might be a start and a run capacitor i think there's two capacitors in here together and this is absolutely required for this motor to work properly so to do any kind of testing with this disk drive on a pc i need to power up this motor with mains ac voltage to get the disk spinning and this is the connector that makes that happen right here now on the model 2 there is a distribution block in the bottom of the computer that takes the mains power and rounds it to the power supply for the machine and then also runs it to this when you turn the main power switch on it powers up the disk drive in fact this is the harness that came out of the model 2. now this is the connector that goes to the disk drive here i think this goes to the power supply or something anyways all of these terminals here were on a screw terminal block that did the power distribution and there were some other cables that went to the iec mains input there was an inline fuse and of course the power switch to avoid cutting into this cable i luckily have another connector that fits into here and this actually came off another eight inch disk drive that i have and i have adapted it with this little coupler here onto a mains ac cord now the problem is of course is that this is not fused i don't know if this thing works the original model 2 would have had an inline fuse on the mains ac it's probably dangerous to run this thing without a fuse in case there's something wrong with this motor could melt this wire cause a fire who knows what so i'm going to run the disk drive on this which is an isolation transformer that is rated about 45 watts it has fuse holders right here so this is fused internally and it has a mains cord here for the us plug and i can plug the disk drive into this and that offers two benefits of course it will isolate this ac motor here so if i touch something exposed i will not get a shock hopefully and then in case this thing is shorter or something bad happens the fuse inside the isolation transformer will blow the next problem is this right here and this is the dc input for the disk drive and that's going to run the drive electronics but also this rather large motor here this motor here is the stepper assembly for moving the head around and as you notice here it's a relatively big and beefy motor it's not like this little piddly stepper motor on the five and a quarter inch disk drive you need something a little bit more substantial to move the head assembly around on this rather large disk drive so to that end this thing runs off 24 volts not something you typically find in a regular pc on the power supply in addition because this is a product of the 70s some of these ics here require -5 volts at least on this version of the drive i think later versions of the sa-800 only needed plus 5 volts they still needed 24 volts but the -5 was not required anymore but this one it does need it the connector down here is also non-standard it's nothing like the molex connector we have on pc disk drives and this is the power supply harness from the model 2. so this large connector goes onto the power supply and then these two i guess one is for the disk drive and one is for the card assembly funny they're both exactly the same they seem to have different wiring in them though but i don't want to cut this or modify this harness in any way for testing of these disk drives well that's where this comes in this is another sa-800-2 exactly like the one from the model 2. this did not come out of a model 2 machine this was given to me by a local viewer here in town actually i got two of these and they came out of some kind of large word processor or something like that i think it was made by nec the rest of the computer unfortunately was sent off to scrap but the disk drives were saved along with the wiring harness from them so i have two of those connectors and also this was the end that went to the power supply and the wires even though they're all white are labeled so with this harness i just need to get this connected to the correct voltage rails and i'll just need to use my bench power supply for the 24 volts and i can use my pc power supply for the plus and minus five because i'll be using my old at power supply and it does have both of those rails available so that solves the problem with the dc power and the ac power but what that does not solve is still how to hook up to this 50 pin edge connector well luckily that's not a problem either this is the original cable that was in the trs-80 model 2. this connector here went to the disk drive controller this went to the floppy drive itself there was only one internal drive and this went to the back panel for hooking up up to three external drives i thought about using a scuzzy cable to make an adapter that would go to this cable and then hook up to a 34 pin connector for a pc controller but while i was searching on ebay i found a seller selling a sugart interface 50 pin to 34 pin adapter which i purchased it was relatively inexpensive and it came very quickly all the way from france i might add has the 50 pin pin header here along with the 34 pin one to hook up to a pc cable has various jumpers to allow you to configure drive select and stuff like that and i think with this that almost completes the connectivity but the one thing i can't do is easily connect this cable or this adapter to this edge connector so i think what i'm going to do is i'm going to take this original cable and i'm going to crimp on an extra 50-pin connector onto this this here is a long scuzzy cable that i've used for other purposes and it has the appropriate 50-pin connector on here that i need so first i'm going to do is get this connector off of this cable and i've already done that where is it here we go you notice there are holes here and that's because i peeled a 50 pin connector off this already to use it for something else i have an x-acto blade in this and i think it should start to come apart and you can see there's a little bit of a gap forming right there i don't need to do it anymore i'm just going to do the other side same thing i know it's not going to be easy to see but you just kind of pry this open and then you start to pull this away and every one of these is going to be manufactured slightly differently the way they're they're made so uh mileage may vary but usually these are easy to take apart and i like these connectors on this cable because they're actually metal the little clips a lot of times they're just plastic okay i'm going to pull the cable out you have to be very careful when you do this because if you're not careful you can actually pull the metal pins right out of the connector so you just have to kind of carefully pull this up now don't worry if they do pull out a little bit because you can push them back in actually at least on the good quality connectors like this there we go so the connector is in perfect shape there is no issues same with this top piece here now on this adapter here it has a little pin one indicator hopefully that's showing up on the camera it's right there there's a little arrow and there's actually a notch in the shroud i guess whatever the part that goes around the pins now of course the notch normally goes into or lines up with what's on your connector but you notice this one is notch less but it does have these grooves here and there is a pin one arrow as well and the grooves always face towards the notch the notch is facing towards the camera and the way this would go on would be like this now there's the pin one notch right there and it matches up with the pin one notch right there so i want to make sure that the cable when i crimp this on that i'm going to be crimping it with the stripe of the cable towards the notch so we know the notch is right there we know the stripe of the cable is right there i think i'm just going to put this like in the middle here now obviously when i put the model 2 back together this connector here is not going to be used for anything it's just going to sit in there so i don't think it really matters where i put it on the cable and i'm just going to take this top piece here so it just needs to be crimped on there basically at this point now there's actually a correct crimp tool to do this work do i have it of course not i don't have that um so i'm gonna have to improvise okay so this is my bench vise and i actually have two slot covers taped in here and i'm gonna use this to crimp the cable i'm just gonna kind of twist the cable around here so i can get it into the vise and i've tightened the vise just so it's loosely holding it right now into position and i'm just looking straight down to make sure it's aligned correctly and it is because all the little metal pins need to be aligned with the cables here and i'm just going to start tightening the vise it's now holding onto the cable itself and it should start crimping there it is i just heard the clicks of those two metal tabs as they went into position it went click click and now i'm not going to tighten it too much because i don't want to crush this connector here it should be crimped and there it is i do have it on the back side but that was on purpose the original cable modified with a 50 pin connector and i know people are going to be like i ruined the original cable the cable's not ruined this cable is still going to work perfectly for what it was designed for and this is a really good quality 3m connector i didn't just use some cheap junky one on here and i just plugged it in and pin one on the connector is lined up with pin one there and it's also lined up with a stripe on the cable so i think this should be good to go for testing now with a pc yes all right so first things first i need to test to see if the motor spins and i'm going to use this disk drive that was from the word processor because this thing was not exposed to the rain there's no corrosion it's just dusty unlike the disk drive in the model 2. so i'm going to pull off this uh whatever's left of the original power cord and this is the cord that i made and the isolation transformer is not connected to mains or yet it is just right here the plug so this connector here which says p28 on it is keyed so it can only go on one way so let's turn this around so we can see the motor turning i always intend to install a toggle switch on this little isolation transformer so i can turn it off and on with a switch here versus needing to plug and unplug this from the wall so in the meantime i'm going to use this little power strip here which is currently in the off position so let's plug this in and here we go look at that okay so it's working this drive is working now it's funny i really need to buy a tachometer or a little device i can measure the speed of things with because i have no way to know what speed this is running at at least right now before i hook this up to a computer now turning this around as i had mentioned this ac motor here is a synchronous motor so it actually is locked to the line frequency well since i have this drive out i know it's at least turning properly i'm going to do the rest of the testing on this drive using this cable and adapter all right this explosion of cables is everything connected up so this is the harness here going to the disk drive and this connection right here is the 24 volts now it actually has a separate 24 volt return which is the ground it seems the power that goes to the stepper motor here has a separate ground so it's okay that i'm running from a bench supply that is separate from the rest of the voltages which are coming from the power supply underneath here and then right here i have the plus five minus five in the ground and i have that soldered on first to a molex splitter right here so that's plugged into the power supply for the plus five volts and the ground and then there's a blue wire that's right here and that's actually going to this isa test card here and i have a pin soldered onto the -5 connector there so that is getting the -5 right off the isa bus now you might be thinking that taking power from the isa bus is not going to have enough power for the disk drive but if we check the service manual here 5 volts is only going to typically take .05 amps so it's really really low current and that's really for bias voltages on the ics on the drive electronics the plus 5 takes 800 milliamps which i probably could have gotten off the isa bus as well but i'm taking it from a molex connector and the plus 24 volts takes 1.3 amps typical which is what i am giving it from the bench supply now luckily the wires on the disk drive end are also labeled for what's what so i did check that i was getting the appropriate voltages on the appropriate pins before i plugged it into the disk drive so i did this testing off camera now this whole setup seems a little precarious and it is but i think i'm ready for testing now of course because the ac motor that drives the spindle is separate from the rest of the drive electronics on this they're not connected anyway i don't need to power up the ac motor to test the voltages going to the drive here i think what i want to do first is power up the dc on this drive without first connecting the cable to the pc i'm expecting the head might move a little bit when i first turn it on but at the same time nothing might happen so down here is the power switch for the power supply and i'm going to reach up to the bench supply i'm going to turn them on at the same time i don't know if it matters that they're on or not simultaneously but i'm going to do it as close as i can it's drawing about 1 milliamp on the 24 volt line which i can see on the bench supply but otherwise this thing didn't do anything so at this point i'm gonna try to hook up this little mess of cables here so i have the pc floppy drive connected uh to the twist portion and i'm gonna hook this up to the drive now there's a few things that play that may cause this not to work right off the bat there's some jumpers on the drive which i haven't even looked at and this is the one from the word processor not the trs-80 and also there's no termination on this drive it doesn't look like there's even a facility for it it probably was on the cable on the original word processor which i don't have there are markings on here for drive select one two three and four it's weird it doesn't start at zero it's currently set for drive select one which would be drive select zero so i'm gonna move this to drive select one or two sorry which would be the same as the way all pc drives are configured and this little pcb has some jumpers to configure for drive select and it currently is passing through what is the drive select one signal which on here is labeled drives like two so that should select this drive i'm just going to ignore the lack of termination right now and let me power this on and let's see what happens nothing seemingly i'm going to go into the bios on the computer and i'm going to set up the a drive as 720k so that's a single density but also 80 tracks now i don't expect this drive to just work with dos and i think that's because the rpms are different and whatnot but at least there should be some activity of the head when it tries to seek i am just going to set this here to floppy drive seek at boot enabled well it didn't give an error about the floppy drive but it also didn't seem to do anything at all i'm going to close this mechanism down so it may think that there's a disc in here and i'm going to run imd which is the tool that i'm going to use to try to control this drive so let's hit t for test rpm oh okay so it engaged this solenoid right here and it's drawing 1.2 amps on the power supply up there so the fact that it engaged the solenoid when it tried to read the disc was a good sign alright so it's not possible that i do anything without an actual eight inch disc and i happen to have a few of them and here's an ibm eight inch disc as you can see it looks just like a five and a quarter inch but much bigger not smaller so i'm going to turn on the ac power which should start the spindle there it is oh it blew a bunch of dust out of it and i'm going to take the disc and i'm going to slide this in it does need to be spinning for it to uh center the disc properly there it is the disc is actually spinning now and i'm going to try to format this disc and i'm going to need to set this up so sides one side double step is off i'm going to set the interleave to 1 because i don't really know what else to set it to and i'm going to try to hit f to format the disk sectors per track i don't know i'm just going to pick nine because i don't really know the right number for this start sector one we're going to do 250 kilobits per second mfm sector size 512 i'm just pushing enter on the defaults and here we go it is actually moving the head it is entirely possible this drive hasn't done anything in 30 years i mean who knows when the last time this drive was even used look at that it actually finished let me pick the option clean head and that's just going to move this head back and forth on the disc a bunch of times here we go look at that it's totally working all right so i think it's actually seeking a little too far because it seems to be hitting a stop over on this end now on imd if i hit a for alignment test it's going to try to read what it just wrote to this disk ideally you should be using a disk you formatted in another drive which you know worked okay so it's not actually reading anything right now at all so the question mark should be showing the number of sectors that's reading back and it's actually not reading anything okay so i wanted to figure out what the format of this drive actually should be and it looks like 77 tracks 24 sectors per track soft sector and a sector size of 128 bytes gives you a capacity of about 250k does say the model 2 has a double density controller so the disc format could use 256 byte sectors and then you get 492k so why don't we give this a try 24 sectors per track start sector 0 let's use mfm which is going to give us 256 bytes per sector and here we go now while this formats there's a couple things that might be preventing this from working first off the there's no termination on this cable and all this assembly here so that could be causing an issue second the disks might be bad i have no idea if these discs works i found them at an e-waste recycler they were just lying around not even in a box so who knows heads could be dirty on here possibly as well the disk drive might not be working there might be some other incompatibility that i'm not aware of i'm not sure so there's certainly a lot of variables it's nice to know that this thing is actually seeking properly and that the pc actually sees the disk drive so that's cool but it is the read write signals that may not be getting through properly or maybe having other issues so with format complete let's see if we can read anything here it doesn't look like it imd is still giving us the big old question mark okay so i'm going to exit out of that i think what i'm going to do is i'm going to take this disk out and taking a look at the head there i do see a little bit of something on there so i'm going to give it a little clean 99 ipa one of these little strip things here i gotta say that disc surface it doesn't look very good it's not very shiny so part of the problem maybe this disc is just bad let me grab a different one i have some more unfortunately they're from the same batch so they might all be bad here's another one and it looks not great as well don't see any mold on it or anything just doesn't have the right shiny look that i'm expecting okay and f to format nope well since i'm lucky enough to have multiple of these drives i'm going to take this disc out of here just make sure it doesn't look damaged no it looks okay let me grab the trx80 model 2 drive see if that works any differently than this one all right model 2 drive first we got to test to make sure that it actually spins up and doesn't cause a problem with the ac so i'll plug that in first just on its own like this let's see if it spins oh it does doesn't sound very good though those bearings when i first took this thing out of the machine the spindle wasn't turning very smoothly and it certainly doesn't sound very good although to be honest now that it's running it actually sounds like it's maybe the grease inside there and the bearing is spreading out worst case i can mix and match parts though take the uh digital board off this and stick it on the other drive et cetera et cetera it's definitely in a little bit better shape all right cut the power there i'm going to plug the dc into this drive and then i move the jumper on the board there to drive select one so that the pc will be able to control it now one thing i read and if i look at the back of the board i'm sorry i can't turn it around to show you but a bunch of the little jumpers that were on the other one have these wire wrapped jumpers so to speak that go from some of the pins to other ones and i seem to recall that if you don't have the external drive connected or that terminator that this thing will not work at all so let's see an imd if this thing even initializes or tries to read it i know the motor is not spinning but we should hear this relay click and no nothing happened at all and i think that's because this drive requires that terminator to be connected so i'm going to connect up the terminator here and it just says disk terminator on it and let's see if that makes this thing behave any differently all right let's see what happens now oh oh hey okay it moved the head it did it turned on the relay all right sorry the solenoid there okay i'm going to turn on the ac motor and i'm going to stick the disc in here well first i should check the head it looks pretty clean close this up this thing is kind of noisy it's the clamp here on the disc so that's not anything else making that noise all right we'll take a look at that it's reading the disc it's having issues all right so let's alter the parameters here so let's see 24 sectors per track uh start sector let's try mfm and 128 and let's write fbfe or no sorry e-f-e-f all right it's having it's it's reading something but it's having errors okay i'm gonna hit f to format this track and let's see what we see now come on all right well it's having errors so if i recall it should have a 24 and a 24 and see how that number it's doesn't show 24 every time in the first column and the second column has a number like three four five something like that that is indicating that it's not working quite right it is interesting it does indicate that that format in the other drive did format this disk um because it's reading something let me jump to like track 30. okay now it's reading nothing so i'm gonna hit f to format this track and let's see what happens all right so it's also having issues there are two screws in here so hopefully i can take this cover off and try to lubricate this clamp here because it's sounding pretty nasty well it sort of stopped making that horrible noise on its own so i didn't really talk about this early on but i can use imd to actually make some floppy disks for the model too now of course because the interface is compatible with the sugar interface i should be able to use a gotek with flash floppy as well i'd like to get this thing booting off an actual disk if possible and i was trying to analyze the disk to figure out what its format is and it sees it at six sectors of 128 bytes which clearly is not right let's see if i can keep analyzing this uh it's not even really working either it's not even really writing to the disk properly all right a little bit of time has passed and watch this yes we actually have this pc booting off an eight-inch disc it's actually working and uh this disc it's full of files and stuff i copy stuff onto it um i do not have the sd card or yeah the sd card booting this is the xt ide it's right here not inside the computer so this is just running directly off this machine now it's unfortunate that i didn't capture on camera the first time i got this working and you can be sure that there was the it freaking works moment when i got this working but unfortunately due to time constraints i had to work on this little by little and i didn't have time to get the cameras all set up to do my testing and yes this is the drive from the trs-80 model 2. so what did i do to make it work you ask well let's talk about it let me shut down this drive here i'm going to start by saying that the trs-80 model 2 drive had absolutely no faults at all with it so really with the problems i was having there were two main issues the first one was actually a software configuration issue on the pc the first problem stems from the way i was formatting the disks and if i'm in imd here and i go to format the disk if people remember originally i was putting in 24 sectors and i was picking either fm or mfm for the encoding fm being single density and mfm being double density so for instance how about i pick the 250 kilobits and with this the sector size is 256 bytes when i format the floppy with those settings in either of the drives when i tried to read it back it just it would really struggle to read back anything i was assuming there was a problem either with the cabling the drive the disk you know one of those things the problem was actually the way i configured the format of the disk this was the wikipedia article and the section within it where i determined how to set up the disk for formatting 77 tracks 24 tracks per sector another 128 bytes for the mfm encoding or single density or the 256 bytes for the double density so that should give me a formatted capacity of 492k the part that i was missing was that when you go to set up the format it is not kilobits fm or mfm it is 500 kilobits per second fm or mfm i think i was thrown for a loop on that particular setting because with three and a half inch and five and a quarter inch disk drives which of course are what i'm used to it's always using 250 kilobits per second when we're talking about double density disks 500 kilobits per second is used for high density disks so i didn't realize that the eight-inch disk drives actually use a 500 kilobits per second data rate that is what they run at and i actually don't remember where i saw it but after reading different articles about it i finally saw one that said the rate was 500 and like a light bulb went off my head and i wait wait a second all my testing was at 250. so i went back into imd and i set it up for 500 just like this same sector size and when i formatted the disk and i went back to a line after that it read it back perfectly it just simply worked so you might be asking now how do i use an eight inch disk on the pc and actually boot off of it well it's actually a lot easier than you think first set up the bios for 1.44 megabyte drive because that enables 80 tracks and 500 kilobits per second because that's what a 1.44 meg drive can use it can use 250 or 500 kilobits per second and then i use the program end format to create a custom format to allow me to format this disk as a dos disk and have it just work with dos so i have two profiles set up here the 500k one and the 654 so i have 77 tracks the same number of tracks as the uh the original trs-80 format and then i have it set for 13 sectors per track and the reason for that is originally i had a 12 actually when i first did my testing with a dos formatted disk and it's because dos uses 512 bytes per sector and remember the trs-80 original format used 256. so it had 24 sectors per track and this has half as much because of course we have sector sizes that are twice as big so originally i had this at 12 and i actually increased it to 13 to try and get a little bit more space out of the disk number of heads is one because this is only a single sided drive physical drive is zero so that's the a drive and the rest of the settings here were just filled in by end format once you you know put in the sectors per track and that's it it was able to format the disk perfectly i cyst it so that copy dots onto it and then i copied some files onto it and the machine boots right up off this eight inch disk and i was really happy to know that both of these disks formatted perfectly in imd with no errors at all so these discs are actually good oh just because it's just so funny to look at but look at the size comparison between the eight inch disc and the five and a quarter inch disc it's just it's so hilarious to see the difference i absolutely it just makes me giddy to look at these eight-inch discs now you notice here in end format i have a disc that says 654k i had another hunch that made me think that i could go higher with a number of sectors these drives run at 360 rpm that's how fast the spindle is on these eight inch drives well there's another drive on the pc that runs at that rpm and it's the 1.22 megabyte high density drive it runs at 360 rpm it has two sides so of course has two heads and it is a high density drive so it runs at 500 kilobits per second well 500 kilobits per second and 360 rpm is exactly what this drive is running at so these discs even though they're larger are kind of the equivalent of single-sided high-density five and a quarter inch discs and of course a pc's default format is 1.2 megabytes or 600k per side and i figured that is even giving a gap space for older 286s and stuff and usually you can squeeze out a little more capacity by shrinking that gap and putting more sectors on each track and i figured there's no reason why this disc couldn't hold as much capacity as a five and a quarter inch high density disc even though if you think about it these are from the 70s so that's pretty cool but i don't know i since i've never used a trcd model 2 or any other machine with 8 inch disk drive i'm not sure that you could actually get this much space on a model 2 because i don't think it can handle those sectors that close together as this 36sx here can so that was it that was the entire reason why i couldn't get these disks to read properly user error i had it set to the wrong data rate and incidentally this 8 inch drive here this is the one i already had is actually in better shape than the one that was in the model 2. both of them work perfectly but this one is a bit quieter in its operation and the other one has some rust on some of the screws like on the spring right here and on the door that this one doesn't have so i may end up installing this one into the model one although either would work and just to retain that functionality with the the loopback thing for the termination i'll probably go ahead and run wires from the pull-up resistors on here over to those pins just just so it if i ever get the external drive chassis i can plug it in and it's actually gonna work without having to open the computer and removing those jumpers now i actually have a third sa-800 that i haven't tested yet and this was in the box with the one i was just showing both of these came from a word processor or whatever theoretically this one should not have termination jumpers on it it doesn't the terminators aren't there and of course that's because this would have been one of the middle drives in the chain and i gotta say this one is really clean inside okay no wait it's dusty it's just upside down but it's funny how the pcb is yet a different color the other one's like a dark green the trs80 was sort of like a bluish color and this one has this uh kind of light yellowish green color i'm noticing here that the ac motor is a different brand i think it's a different brand the color is different that's for sure anything else look different no this all looks pretty much exactly the same anyhow since i have the whole rig out here might as well test this drive out and see if the third one works just so i know that it works because up until this point i've stored these away because i had no easy way to test them okay here we are on imd let's see if i can read the disk it does not read i'm gonna take the disk out and try the other one okay try number two dir a colon no it's still not working and look at that imd just cannot read this drive at all fascinating just in case this is not some kind of an alignment problem with this drive i'm going to try to format this disk with end format here nope immediately it says unreadable so that means that this drive is not working just to validate that is not something else that's wrong i'm going to swap to a different drive again we'll try that this drive is actually a bit quieter when the disc is in there and this is latched i think the bearing on this one is a bit noisy it kind of makes this worrying sound that i don't hear on here all right back in end format i'm going to try to format this disk here we go there it goes going very quickly and if we go to imd and i go to a line it'll have no problem reading this disc it just formatted successfully okay so at the top you see 1 through 13 that's all 13 sectors uh 512 bytes each and if i go to track 50 there we go it's still reading 26 and we go to track 70 still running 26 so yep totally totally working so there's an amazing github repo model 2 archive they basically have all of the software for the model 2. it's all here and i've navigated over here to the tandy folder and i'm pretty sure i can find the operating system in here you'll see there's tons of stuff there you go trs-dos like 2.0 here and look at that ts-dos 2.0 imd single-sided floppy drive for the model 2 so that's the exact file i want i downloaded the repo so i can grab the zip file so here's an image of it i'm 2.08 i'll probably make this one actually for the model 2 all right here's ts dos 2.0 i'll just copy this onto the sd card for this thing all right in imd i'm going to hit w for right i have the disks in this model 2 folder there it is ts dos uh there was three files here there's a blank disk there's one where a bunch of files have been erased you have more free space and then this is the original copy of the disks so we're going to pick that here city model 2 trs dos disk operating system 2.0 a and we're going to hit enter here we go should write to this ah 26 sectors of 128 bytes oh the first track was actually fm or single density and now it's writing 256 bytes which means that the rest of the disk is actually double density the trcd model 1 did that as well and that's because the original disk controller on the model one was single density or fm modulation and later upgrades brought it up to double density but the roms inside the trc model one can only read the fm or single density track for booting and then that track tells it to switch to mfm or double density and that's clearly what's going on here with this thing as well i wasn't aware that it did that but this ability to write both single density and double density on a single disk image is one of the reasons why imd is such a great program for this exact purpose i am noticing that this wikipedia article is wrong about the 24 sectors per track it's actually 26. and that's evidenced by what we're seeing on the disk image itself here 26 sectors of 256 bytes or 128 bytes this is definitely a slow process but at the end of this i'm going to have a boot disk that i can actually boot the model 2 into an operating system and that archive which was like 5 gigabytes in size has all the other software i could ever want for the model 2. there we go i've successfully wrote the disk and what i'm going to do is just apply this label to the disk there it is well that was a little bit of a marathon i know this video is super long i'm going to try to put index marks in it so people can jump to different sections maybe about termination about how to write the disks with imd things like that um but i am ecstatic i think i was really dreading the whole disk drive part of the model two and now this thing works i know i have two good drives at least hopefully i'll be able to fix the third one that'll be a future video so get subscribed for that but i know now i have a boot disk so when the model 2 comes together if it indeed works i can actually boot something up i'm really excited about that i'm hoping on next week's video i can get the model to assemble to a point where i can power it up and see if the circuitry in electronics actually works and if it does then i can boot this to an os now i know i won't be able to type anything because that keytronic keyboard is a disaster and i have to re-foam that whole thing and uh trying to work on this in my spare time means that it can be a little bit difficult so there might be a little bit of a gap between this video and the next model one video but don't worry it'll be coming up because i've made a lot of progress on the model one uh when it comes to repairing the rust and cleaning all that other stuff so watch for that i want to thank my patrons whose names are scrolling up the side of the screen right now if you want to become a patron yourself you can do so there's a link in the description don't forget to check out my second channel um i got mail call stuff and random stuff over there lately it's been a lot of mail call items but uh yeah they'll just be cool random videos and don't forget to get subscribed and put your comments down below and i don't know all the usual stuff and um yeah big thanks to uh local viewer here who donated uh this machine to me it's been quite a bit of work so far but kind of cool nonetheless kind of fun and exciting as i as i make progress on it all right that is gonna be it so stay healthy stay safe and i'll see you next time bye [Music]

Channel: Adrian's Digital Basement

Views: 294,397

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Id: TfEzjcG_0gs

Length: 54min 48sec (3288 seconds)

Published: Sat Nov 06 2021