The T.Res chip is actually a resistor network. Termination Resistor is what the name stands for. It only needs to be on the last drive in the chain, and also is only needed with some early floppy controllers. Newer controllers terminate the bus on the controller card.

Games that were designed to run on a wide variety of cpu classes hook the PC's interval timer circuit and use it to synchronize the screen updates. Thus you can have consistent game play across machines of different performance. Grand Prix Circuit is one of these games. Once you have a CPU that exceeds the computation power required to play the game without bogging down it spends time in an idle loop until it is required to generate the next frame.

Love the video and the topics you explore! Unfortunately, you picked one of the worst games to showcase CGA RAM speed: Grand Prix Circuit is internally framerate-locked to 10fps, so it looks the same on any 286 or higher. A much better game to test how CGA RAM speed affects gameplay is Jet 2.0, which updates the screen with REP MOVSW and can run as high as 60fps on fast hardware. Otherwise, using a benchmark program like you did in the video is the only way to reliably measure speed changes. It is difficult to find games that can reach 60fps *and* support CGA. This is because, in the era of programming for CGA, it was impossible to reach such heights, so programmers cut corners that would never cause an issue with speeds of the time, like lock the internal framerate calcs to a low rate (10 Hz, as seen in Grand Prix Circuit). Or worse, not lock the framerate at all, so you see some games become unplayable on CGA on faster systems whereas the same game works fine on EGA because the timing is locked to the page flipping rate of 60Hz; Stunt Driver is one such game that comes to mind.

Man, I used to play with Fractint on my 486 back in the 90's. So many memories.

the bad adjustable colorburst cap could have caused excessive noise back to the CPU clock line, IBM PC and XT boards both used a 14.318 mhz crystal and I -think- it was divided down for various functions in the machine including the CPU clock IIRC.

Thank you for the awesome video again. I just acquired an IBM PC 5160 and all repairs regarding that era of hardware is very interesting indeed.

Nice to see the IBM working well again! The 486+CGA combination was something I used a lot back in the day, on a VGA card though... I had a black and white monitor and the strong colors helped with the contrast in games!

About the dip package that one of the drives lacks, if I remember correctly, old disk drives didn't use the twisted cable to identify the two drives connected to the same cable, so I guess the component is a terminator.

Lets take a moment to appreciate all the cool hardware in the background!!! The kitchen workshop is fantastic Will!

I read that this IBM 360K floppy T-RES terminator resistor chip should be installed on the last floppy drive in the chain and it works just like SCSI bus termination, to prevent the reflection of electrical signals from the end of the cable in order to ensure reliable operation. Cheers.

2:45 "black & red = dead" even when I wasn't so fluently speaking English back then, we've been teached this rhyme back then when installing hardware. Before ATX came out. Thanks for your content!

I suspect that the 1/3 option in the bios is not really working and it's actually still 1/4. You could test this by meassuring the frequency directly from the ISA slot (pin B20), if you have a multimeter that can do that high a frequency, or an osciloscope.

I always love this kind of mix of non-era part. Way back I ran an ATi Small Wonder with an amber monochrome in a Pentium 3 board. It ran as a Linux server for a while. Later I used it as a networked music player using mpxplay and a dos smb client.

When my VGA monitor died, I used for a short time (few weeks I think) a original Hercules adapter. I also had a CGA card but no monitor to pair with. Luckily the Hercules I had was paired with a beautiful amber mono screen. My first shock was when I entered the BIOS setup. My motherboard had winbios (graphical UI) but it was unrecognizable with that Hercules; it was displayed in a strange text mode. The next surprise was that Win95 was not able to boot with that card. So i took another HDD with ms-dos to use. The time I spent with it, was entertaining, it was like a lottery to run programs; would it run? and if so, how will it look? I also used a CGA emulator for Hercules that allowed to run CGA games on that mono card. I also remember that the only GUI OS that worked with Hercules was Red Hat Linux (ver 7 I think it was) that I installed and ran fine with X server GUI only. Win 3.1 or 3.11 would not run in mono, only Win 3.0 was able to. The only drawback was that I had no idea of Linux and no manuals available, so no way to learn how to do something useful with it. So I returned to Windows as soon as I got a new monitor.

That variable capacitor (not a variable resistor in this case, btw) was most likely used to tweak the signal coming from the crystal next to it. I assume the crystal is related to the system bus clock, and that could explain potential ISA and floppy drive issues.

Its good to know a 486 board still works with CGA card. I have a card that needs to be tested so will give it a whirl.

This is quickly becoming one of my fav channels, great video!

I like your new format. Please keep up the great content!

Another excellent video. Always enjoy watching your content. Love the old PC.

My first "proper" graphics card was a Cirrus Logic 5429, a VESA "Windows Accelerator" with a whole 1MB of memory. I was so proud of that powerhouse of a GPU.

That CPU install blew my mind. Those pins and not needing a cooler

The RED on the IBM Monitor looks really good.

Loved the CGA demonstration! Great work here. Thanks for sharing!!

Some of the new retro games that run under DOS target the improbable combination of 486 with CGA (e.g. Castle of Viana). Now you have the ideal system for them! It was nice to see the IBM back to being a happy computer in the second half. Hopefully it will get its voice back soon.

As I had a 486SX back then, I wasn't surprised.

T-RES stands for terminating resistor and it is used to tell the PC bus where the last drive on that control line is. So if you have two floppies, if memory serves, the resistor block should be on the B drive. If you have an XT with one floppy drive then the only floppy drive, A, should have it installed. Hope this helps.

termination resistor

I believe the reason why you only get a few different benchmark results on the CGA card is the wait states. The algorithm (implemented by the discrete logic on the CGA card) is basically: 1. wait 1 hchar, 2. wait for the next lchar boundary, 3. wait for the next CPU cycle. Step 3 will be negligible on a 486 so how fast you can access CGA RAM is limited by how well the access pattern of the benchmark code fits the CGA wait state algorithm. With a different benchmark you might get different results as to which set of FSB divisors give the same performance as each other.

One (very late) comment on the racing game. It appears to use a graphics technique sometimes called beam racing. In order to horizontally scroll different regions of the screen at different rates, the game will update the frame buffer pointer register in the 6845 CRT controller at different points in the frame. This must be done continuously at the frame rate and with consistent timing during the relevant line blanking interval in order to ovoid very obvious jitter. This would probably place an upper limit on the game performance unless it was recoded for faster CPUs. If interested, KZfaqr James Sharman has a video dedicated to this topic in his VGA From Scratch mini-series (an amazing DIY hardware and software project).

You may need to move that T-Res chip to the B: drive if you want to continue using it. Although it may not be making much difference yet, that chip, which is a set of 150 ohm (or somewhere about) resistors is used for terminating the floppy drive cable and prevent signals from bouncing around. That may also have something to do with issues you've had out of it in the past. Check the Shugardt floppy drive standard for specifications.

Check with modern vga if it goes faster, if not, the game has fps control, or the speed of the physics in the game are not related to the rendering process, they are independent. This is done in games mostly playable on a network.

My 286 PC has some similar issues to your 5150 where programs/games will just crash constantly in random places, seemingly even more so if you have more ISA cards installed. Really wish I had the skills to identify the issue and fix it, there's no RAM issues detected or anything like that when I run something like PC-CHECK.

Terminating resistor package.

I have two of those lovely 486 boards with pci, one is bricked, from a short circuit on the back. If someone wants to have it for spares let me know 😂

On the answer to the question "Why" there is an 8 bit port.. The simple answer is: BEFORE everything was integrated in the motherboard, you really needed those expansion slots.. plenty of them... and.. 1. Cost.. and 2. Motherboard real estate. Well.. the CGA is ONE card that actually DEMANDS it, because of the form-factor going down so a 16 bit slot would be in the way, but it wasn't alone. .. and.. if you buy a card (with special functionality) for one computer.. you pretty much don't want to be FORCED to give it up for your new computer. F.ex. I have a blind relative that had a speech-synthesis specific card in his computer. That was a full-length 8 bit card.. It cost a shitload... and I don't even think they ever made it in a 16 bit version, because suddenly people just had to have a sound-card and with a Soundblaster 16- and with the speed of computers, and available memory: By the time you had those- it was all done in software. .. but there was also a shitload of 8 bit cards that.. TECHNICALLY could've been mounted in a 16 bit port, but they still were only the 8 bit cards. Most people think of the ps/2 mouse as standard. That was not yet the standard on 486. 486:es were still being created when it finally DID become standard so newer motherboards may have a couple of ps/2 ports for keyboard and mouse, but most people had to settle for something else. Serial mice?.. they actually grew in popularity fairly late, so it was VERY common that the people who manufactured mice sold them together with a dedicated isa-card for them.. my first mouse was of the brand "Mighty Mouse", and it was such a bundle which had to come with it's own card and special drivers. LATER serial port mice became popular, but tbh.. If you had a modem (almost ALL modems during the 486 era were external and connected through a serial port.. I SUSPECT due to the interference problems).. Then I also got an MM-401 (mpu-401 compatible) midi-card. The thing is; We had a Roland Sound-canvas module.. I used it with my organ, OR with my computer. It was the second revision which is when it finally came with a MT-32 sound-set that you could switch to if you wanted to play any actual game.. While people were listening to FM-music while playing games, I had a full symphony orchestra while playing Might and Magic 3, or Sierra games.. (If memory serves; Even doom did support Roland sound).. Of course one wanted a soundblaster anyway.. or more exactly: Also.. because it played recorded sounds, so all the sound-effects in most games.. So.. Just sound took two slots.. Then of course.. there was the advent of CD-rom drives for your computer.. hint: They were NOT IDE compatible at the time.. you needed a special card to be able to use it... Since the actual transfer speed was 150kb/s.. you didn't need much bandwidth: Save money by only supporting the 8 bit bus. That said: A LOT of sound-cards had various CD-rom interfaces on them. I bought a bundle from Creative-labs, so I had a Soundblaster that ONLY had the ONE interface, but it WAS the right one (fortunately; I know people who bought the card and the drive separately, so DESPITE there being one or even as many as THREE different interface ports on the sound-card they STILL had to mount a separate card for their cd-rom drive).. Of course.. I was NOT helped by the fact that my soundcard supported it. Not much anyway, because I needed my CD drive to be external. Which WAS what the bundle was for, BUT.. it came with an extra card in order to move the soundblaster pro's internal port to an external connector. While we still were using a 286 we also had gotten a VGA card.. more exactly an Ultra-VGA card.. same amount of memory, but supported some extra modes.. most notably 256 colours in 640x400 mode (Our windows looked better than anyone else's and they had 386:es, so we really could make use of coreldraw).. And that was of course also an 8 bit card... the 640x400x8bit was of course nothing to play games on, but still.. we kept that card for a LONG time.. It was when we updated our first 486sx25 to a 486dx33 we finally got a trident 16 bit card. So.. cards I had in the same 486 that was 8 bits: Graphics, MIDI-card, Mouse-controller card, CD-Rom controller, and the serial/parallell port cards. I THINK The IDE was 16 bit, though.. while we had a 386 we were still using our harddrives from when we had a 286 and they were both MFM-drives and the controller for that was 8 bit.. Just to say; We had started with a 20 Meg drive.. then bought a 40 meg drive.. and kept the 20 meg drive.. BUT.. then we bought a different controller that used a different scheme for packing the data, so we literally had one 30 meg and one 60 meg drive.. "for free".. where the biggest drive anyone could have if they intentionally splurged was 120 meg.. but those two drives died after a while. So.. yes.. During the era of 486.. I DARE say that pretty much 100% of people had AT LEAST one 8 bit card in their computer.. AND a lot of people had many cards in their computer.. so.. doing ONE card so it CAN handle odd format 8 bit cards wouldn't even be a "lost port" for the people who didn't use a CGA or some other card that literally required such port, because it would still just be just another port that wouldn't be in use.

There is a reason the "TURBO" button existed on the PC/AT computers. I'm sure this board had the turbo button connection on the header.

I'm sure you already know but the mystery "chip" is a terminator block.

I have a retro computer that is rather a Mac Plus than an IBM with a similar symptoms in the built-in display screen, which maybe might just have had some dirt between solder contacts of the HV output to the CRT causing it to ripple and flicker. I’ve never examined it internally, in spite that there was no compromise the last time it was used.

chip on the floppy is resistor network (terminator)

Lucky me! OLDest x86 is a 1994 Tulip Socket 3! 1981? hmm, can't get any closer than my C64 'breadbox' with Grey Fs...main use = 1987 to early 1993. (BUT still alive!)

I think the variable capacitor adjusts the OSC signal on the bus, which can be used for all sorts of things, including affecting the DRAM refresh timing on some motherboards. That could explain why you were getting what looked like ram faults in addition to weird behaviour from expansion cards making use of that signal.

Hi, nice video. About the CGA snow effect, i know it's due to the contemporary access to video memory by cpu and cga. I think it's because while the cpu is accessing the memory the cga get bad readings or it is blocked from fetching display data. I also know that not all CGAs had this problem. Do you know how they fixed the issue in snowless cga cards?

To my knowledge, CGA either Black White Cyan & Magenta, or Black Yellow Red & Green colour pallettes, how was the game at 4:24 showing Black White Cyan and RED? How was it showing that combination of colours? Also the demo with spinning shapes is more than 4 colours, how it that possible?

Looks like that floppy chip in question would be a terminating resistor pack. Likely should be installed on the last drive in the chain. Maybe early floppy setups were noisy and needed a t-res? Ive never heard of PC's needing a terminating resistor on a floppy chain as a requirement.

_Before I say anything else, a brief apology to PCRetroTech for leaving you hanging on the CGA improper on stock thing: It likely (my current guess: 95%) would not after all work as I expected, though there might still be an outside chance (5%). I've not followed up and not gotten back to you because I got sidetracked and overwhelmed, including mentally, and I guess that latter part now includes that there's a war - almost beyond comprehension. In principle I still would like to get back to you on that one day, but in the meantime you're probably reasonably safe in assuming I was once again talking nonsense._ On plugging stock CGA into newer boards: Been there, done that, didn't know about the whole what's clocking what when I did it. The interesting thing is that at least well into the nineties and noughties, boards routinely used to have that one 8-bit ISA slot (and I wouldn't exclude the possibility that perhaps some ISA-compatible boards still do), though I'm not sure the board designers always understood why. That's because when I last plugged my IBM CGA into a maybe 386 or 486/Pentium board (hard to remember which), there were a bunch of ICs and various sufficiently tall components behind the 8-bit ISA slot that actually physically blocked things, so the CGA could not be fitted into that slot. What I ended up doing was, I cut out the very back at the end of one of the 16-bit slots, and then I used some simple insulating material, it might have been just a piece of paper, and wrapped that around the rear bottom edge of the CGA card, so I could physically push the card into both the non-insulated 8-bit part as well as the insulated 16-bit part of that slot - so that it fit but nothing in the 16-bit extension slot made contact. It wasn't pretty, it required cutting out the back of that 16-bit slot, but it worked. There was nothing else in the way behind that particular 16-bit ISA slot. I don't think the single 8-bit-only ISA slot that routinely was on boards back then was there for any other reason than to accommodate large cards whose PCB dimensions resembled that original CGA. But I think including one 8-bit ISA slot was one of those things everybody was doing, but not everybody who was doing it remembered why they were still doing it, and that resulted in mainboards whose inclusion of an 8-bit ISA slot was kind of useless -- like the board I had. I guess you could still justify that 8-bit slot as "Hey, you can fit a short ISA card in here without the slot taking up more space on the board", but then, why not just add another PCI slot instead, because we're prolly well into that era at that point? It's a nice little litmus test: If there isn't a "firebreak" of only low-profile components behind that 8-bit ISA slot, the board designers didn't know what they were doing. Which was probably common, I'd wager.

Grand Prix Circuit has a conceptual framerate limit or something. If you use the successor game, Grand Prix: The Cycles, you get an improvement in framerate/smoother gameplay.

The 8 bit slots have loads of uses - there are other expansion cards other than video cards you can plug into them! Scanner cards, i/o cards, modems, specialist interface cards, etc, and why would you want to waste a 16bit slot on an 8bit card!

I have a OPTi VLB/ISA board that is from 1998 surprisingly, it was sold as a industrial board. it has the AMI WinBIOS

is there anyway to override the coiors in the palettes?

What would be funny is to find the newest computer you can that would take that card. You might need a slot extender to make it fit onto newer boards. I wonder if it can be made to work on PCI only boards using a PCI to ISA adaptor ? if that exists

0:10 Your hand shows the older 8/16-bit *emulated* PC/AT-bus (black slots) as well as the never 32-bit bus (brown slots) going *directly* to the 486 CPU. Cards normally use either one of these, not both.

Termination resistor

So I watched over half of this and I guess I missed why you shouldn't put a 1981 graphics card in a 1994 PC except for some CPU speed issues? It looks like it worked just fine except for the required tinkering for the bus speed. Is there some reason I couldn't put a Hercules in any ISA slot and use it with appropriate software on any PC?

My guess would be that the blue chip is a terminator of sorts.

I had a board almost like that. I stuck my internal modem in that slot.

What is the name of the first game? childhood memories, excellent video.

Maybe that potentiometer had shorted something. Or Maybe it caused interference through capacitance.

Never heard it called a four eight six.

Don't you think that some games would sync to the frame rate, and thus not run "too fast"? They might do better, finding they have more time for computation, but still present the game world at the proper speed. For all but the most trivial games, I doubt that it's just looping as fast as it can and thus the write speed of the CGA memory and registers bring it back to original speed.

why do people always use those old CRTs with shrunk down picture? why isnt it streched to fill whole screen?

Wait states?

Will it worck in a soket 7 theoreticly

Would the MDA card work?

Hi There is limitation to the ISA bus, it does not always run at 4.0mhz, they are fairly robust and can be pushed and run up to about 20mhz This is what the clone market done, as they pushed the XT into the Turbo XT territory, they also found tweaking the bus helped, as you mentioned no good having the cpu doing 8/12/16/20 mhz is the bus is fixed at the original slow speed. As for software / games. The original PC/XT were all the same speed 4.7mhz, so you just coded, there was no need to think of CPU speed With XT Turbo, AT / 386 days, old programs were just running to fast - like your zaxxon, the game has done all the clock cycle calculations and yes you were to slow on the keyboard, all those non-movements from you means crash Try playing space invaders or frogger, you are dead by the first or second keypress So programmers wrote some test code, either hardware probing or some nested loops and get the elapsed time / clock ticks taken - then factor that as a percentage of the XT, this gives you some software wait states This is where turbo C and turbo program programs have that divide by zero crash, as the nested loops on newer machines are done under 1 second, as a integer it is divide by zero There are some good old tools and test programs for video cards and hardware rating, no 2 give the same result :) i find nortons sys info ( version 5 ?? ) fairly good Regards George

That's a variable capacitor btw

So why shouldn't I put a graphics card from 1981 in a PC from 1994 ?

Turn off cache in BIOS and even zaxon will run fine.

Hey mate.. using a red line on your thumbnail makes people think they already watched

YOUR FLOPPY CABLES ARE CONNECTED WRONG, REVERSE THEM.

Always nice to see a video that shows the complete opposite of the video title, just so I get to exercise my downvote muscle.

For the love of god it's "four eighty-six", not "four-eight-six".