I needed this video 30 years ago.

DX2 at 66 is faster than DX4 at 75 probably because of faster FSB

For the 4x multiplier just isolate the clkmul pin of the cpu from the board and manually pull it to ground (or check if it goes to any resistor or jumper like the clock generator did). Ive literally played the same game on mine which is a siemens nixdorf d819 motherboard. I just connected it to chassis with a wire and its happily running at 160mhz giving around 1300ish realtics in doom. Note: a 5x86 ADW didnt like the 4x40mhz no matter of any overvolt even at nearly 4V. I changed it to an 5x86 ADZ and all good.

When i was a kid, I exploded a 286 trying to overclock it by replacing the crystal on the motherboard. I had succeeded in making my 286 run super speed, and was going for Warp Speed when the chip when POP with a cloud of magic smoke and a huge blast of shattered silicon. It was AWSOME, and I'm thankful my uncle gave me the junk computer parts to play with. At school we were running 486's and upgrading to Pentiums, but at home I was moving from 8088 to 8086 to 286 to 386. always a few generations behind so parts were plentiful and i could do stuff like overclock my old pc when I got an upgrade. I was trying to make the 286 run more than 2x faster. It worked at 1.5 speed. It was working at 2x speed for something like 15 or 20 seconds before the screen stopped counting the memory. then the screen went blank, and POP.

We Kids tuned our 486s all the time for our ethernet / doom sessions. My brothers final config was an amd 2x50 MHz mounted to the wall w/o a case and I had an intel 3x40 MHz. Happy times until quake killed the 486 😂

Back in the 90's a co-worker learned about the clock generator's 80mhz feature, and was able to run a DX/4-100 at 120mhz. He had to add a fan to keep it stable

We were actually playing around with some AMD 133mhz 486 chips last night. If you can modify the board to a 2x multi to get 4x, try leaving the fsb at 40mhz and put a heatsink on it. We ran 8 different chips last night, All ADZ models were stable tbrough some quick benching,1 ADW was too but 1 ADW wasnt able to get past post. Reading online the ADZ models are the ones that are more likely to be overclocked as they are the newer ones. Enjoying the videos mate!

I miss the days of crazy overclocking and hardware hacking. It’s a shame that the newer the hardware, the more it gets locked down.

Doom always seemed to really like extra bus speed over raw speed. I found this out in 1996 when I ran my AMD 5x86-133 both at 150 and 160 mhz, and left it at 150 mhz because both Doom and Quake were faster on the 50 mhz fsb. I had a very tolerant Diamond Stealth 32 Vesa card for video, and Quake was 'playable' with that setup until I finally saved enough for a Pentium 120 later in the year.

I'm very interested in the next video! Back in the 486 days I had a Packard Bell PC that came stock with a 486 DX2 66MHz. I later upgraded the machine to a AMD 5x86 133 CPU also using an in socket voltage converter. In my case I ended up having to set the board to 40 MHz FSB and used a 3X multiplier for a final speed of 120 MHz At the time there wasn't a way to set the proper multiplier and this was in the very early internet days so I had to go with the info that was etched onto the board itself. About 6 months before I did the CPU upgrade I also did a L2 cache upgrade from 0KB to 128KB. I read an article in a computer magazine where that was done on a different mainboard that had empty cache sockets that was similar to mine. I got lucky in picking out the correct cache and tag ram chips. The L2 upgrade also provided a nice speed boost in many things.

Now this is the kind of hacking that I love, wish there was more similar content anywhere.

That board is also supposed to support the Original Intel i486DX-50. I wonder how you enable the FSB to run at the same frequency as the clock generator instead of half. Then you can try to overclock the AMD CPUs to have FSB of 60 or 66 MHZ LOL! I remember when I was working at the computer store back in the 90's we had over clocked a DX50 to run at 60 or something like that. It was awesome at the time!!!

The appropriate pin on the Socket 1 diagram for the CLKMUL signal must set low (i.e., shorted to V_ss) to enable 4X on the Am5x86. That pin is possibly desigated R-17 on the Socket 1 layout.

Totally different MB but I also had an AMD DX4/133 or 150 or something and I could run it with FSB of 50, 60, or 66 MHz and clock doubled or tripled with VLB hard disk and video and it was a screaming machine. I think it wasn't stable at 66MHz but at 50 or 60 FSB it worked.

I'm not surprised by the performance boost in the DX2 at 66mhz over the DX4 at 75mhz. The 486 is really limited more by the bus speed than the internal clock speed of the CPU. So running a 33mhz bus will tend to net a bigger performance gain over a 25mhz bus. A DX4 at 100mhz (33mhz bus with a 3x multiplier) would potentially get a nice boost over both, but the 5x86 is still going to beat out any 486. All this makes me want to try to overclock my IBM ThinkPad 701c with a 5x86 in place of the DX4 since I've read people use to do that to them back in the mid 90's. But as that is all SMD in a small laptop I'm afraid my limited skills would end up damaging it.

You can hear your excitement in your voice when ole DooM is ripping fast! Great video, great hack! Well done!

I've got a fever, and the only cure is. IBM motherboards and old CPU's.

What a great hack. It's really interesting because I've got an Ambra 486SX/25 and the board is manufactured by IBM - same black PCB and the layout is similar. However, it has jumpers for 25, 33 and 50MHz. This is confusing for two reasons: 1) because of the lack of jumpers on the PS/1 board and the lack of 50MHz, and 2) because I don't know of any 487 that ran at a 50MHz FSB. I might do the hack in your previous video to see if a 50MHz DX runs stable in my system.

Looks like the IBM PS/1 is a bit of a sleeper 486 system. Very impressive CPU figures when you know what to hack and replace to get max performance with the resistors and the socket interposer.

A superb series of videos so far!

This is very good stuff! Honestly best upgrade series I've seen in a while that desktop form factor ps/1 dx2 66 is my first PC. Wish I still had one

Cool content Roman! Right up my alley 👌 I have a similar setup on my Compaq Presario 425, which is wired to run at 33MHz and is then multiplied x4 by my Evergreen 486 upgrade which is essentially an Evergreen OEM "Socket Blaster" with an Am5x86 running at 4x33MHz=133MHz. The original Compaq Presario machines were in fact Compaq's versions of the PS/1: Cheap, low end machines for home users, which makes them even more fun to tinker with and get the most performance possible out of 😎 P.S. the DX4-75 is slower because the on board local bus graphics card and the memory is running at 25MHz instead of 33, which makes the DX2-66 faster. Memory/bus speed is often more important than raw integer speed of the CPU itself, which the DooM results demonstrate here 🤓 The i486DX2-66 was in fact the ultimate sweet spot between bus speed and raw CPU speed, making it a very stable and well performing platform at the same time, especially with its VLB implementations @ 33MHz, which is what made it the most popular 486 CPU ever made.. Love the analog synth tunes in the background. Did you make them yourself? I noticed the nice analog synth gear in previous videos ;-)

It was rumored .. 'in the day', that the IBM 80 bus could easily be clocked up to 80mHz..perhaps even to 100hHz. I had a PS/2 50z that I upgraded with a socket conversion to a 486/7 AMD type chip, but the bus was still at 25mHz.. and the add-on video board and RAM was the reason that I didn't even think of up clocking the bus.

This is a cool video series, thanks for making it :)

I've assembled myself a monster 486 board with a DX5 and overclocked it to 160MHz, at which point it was approaching P-75 levels of performance. But even with a VLB video adapter, it would still be slower at rendering frames, than the slowest Pentium. 55.5 in 3D Bench. Manual listed supported chips, like the main clock. I ended up buying everything to speed it up to max. For some reason DX5 only ran with 256KB cache. I had 512KB originally and that wouldn't boot. I checked the chips, they're functional. Just something odd. I read on forums that some had the same experience. DX5 not liking 512KB.

IBM engineers cringe every time you put that soldering gun on the board to unleash their 'hidden features.' 🤣🤣🤣

You're lucky because those board you have are the latest model IBM released. Earlier one arent so upgrade friendly.

You are amazing ! Your Hardware Skills are great. Keep on with your IBM and the IBM keep up with you ;-)

Awesome video as always,

The crazy part of this video is that those cpus are benchmarked without any heatsink or fan...

I have one of these IBM PS/1 towers, just like yours. Mine came stock with a 486 SX 33mhz. Mine is the Consultant 2168 -E57

Love this kind of mod, great work!

Great video!

back in the day with dx2's we used to build always had a heatsink and fan... sx25's dx33's didnt need them, a lot of old vesa cards used to choke @40 and 50mhz , for DX50 rather than a DX2-50 or DX2-66 we used to advise to put an ISA card in for stability - and would always advise the customer to go to a DX2 CPU instead.. also memory could be problematic @ 50mhz bus speed

Yeah the bus speed affects Doom a good bit. An SX at 50 on 50 bus outdoes a DX2 at 66 on 33 bus by a good bit.

Perhaps those "clock" jumpers, that are documented in the PS/1 technical manual but in an obscure fashion (possibly not implemented the way the diagram suggests on the average 2133/2155/2168 motherboard IBM shipped) provide signal to R174, R175, R176, if they are all populated with 330Ohms and if the installed crystal and CPU combination matches the intended multiplier settings?

Really good project!

The buck-converter you have definitely has ripple, but you need to measure output voltage only loaded! And beware the smd trimpot is very unreliable, better measure the real resistance and replace it with the smd resistors. /*with the time the trimpot can go crazy because of moisture and dust*/

These videos are great!

Isnt socket blaster handles multiplier configuration pins? If its not, you can snap off that pins and configure them with come wires directly.

Back in the day 30 FPS in Doom was considered 'snappy', hehe.

So you're now close to the minum spec for running Doom in realtime. Maybe you need a little more to be safe in more busy locations.

Excellent.

Well, Am5x86-P75 @160Mhz incoming 😂😂

That AMD 5x86 was the first big upgrade I bought with my own money back when I was a teenager. I went from a 486 DX2-66, so as you experienced for yourself, I also saw decent increase in speed in Doom and other games, but it wasn't as big a performance increase as I expected. Certainly not the Pentium levels of performance that AMD claimed. That's probably down to the 33MHz FSB, compared to the 50-66MHz of the Pentium. In hindsight, I probably would've been better off buying a second hand Pentium. I think this would've been around early 1996, so there definitely would've been plenty of 100/120MHz Pentiums on the second hand market by then, possibly the odd 133MHz systems. But I didn't find out about the local computer markets until later, so it would be a couple of years until I could afford to upgrade again.

I had a 2155 - wish I never got rid of it!

According to IMISC418 datasheet 60Mhz configuration was 88Mhz before E revision. It might be interesting.

I like this hacking, especially that is the IBM board from the era where they tried to lock down everything about PC and (thankfully) failed 👍

Set clkgen for 2x 33 MHz (66 MHz, like the DX2). It should work as 4x this way

YEAH! Awesome conclusion to the videos. There are still some more to come, I hope?!

it would be cool to mod one of those boards with jumpers and 330R resistors so you could switch freqs at will.

IBM just wanted to rip off customers. If the PS1 were sold running at full capability, they might remain in the home market at least longer

Now put an 83mhz Pentium Overdrive on the '486 socket! Then get a riser card that has PCI slots and add an evergreen technologies 550mhz Celeron-on-a-card! :D

i would trace where yhe clock goes, maybe an unpopulated resistor pad like in this video

Faster FSB... Everybody from that age of processors know this by heart.. you must be young ;)

This is a really good looking pc

The DX2/66 putting out (slightly) more FPS than the DX4/100 doesn't surprise me, because in many cases, bus speed (as opposed to internal CPU clock) is your main bottleneck, especially in doing stuff like pushing graphics out to the graphics card, etc. With the DX2/66, you're running at 33 MHz bus, whereas with the DX4/100 you're only running at 25 MHz.

An 83MHz Pentium Overdrive ( PODP5V83 ), aligned approrpriately with the inner matrix of pins on the Socket 1, with free-hanging pins (and possibly a wrap/bodge wire to the write back pin and the appropriate pin on the motherboard chipset) would be faster than this Am5x86 at 133Mhz (or 160MHz). If you want to try something even crzier than this in the future.

FSB is more important than clock speed in general

DX4-75 means that the Front Side Bus (FSB) is running at 1/4 if 75Mhz (18.75Mhz) while the DX2-66 means the FSB is running at 33 Mhz. If I recall correctly it was cheaper to buy a DX4-75 than a DX2-66 way back when. Thank you for the video!

You should have a load while adjusting the voltage to the cpu. Preferably the same as the cpu uses. Can Socket blaster be rebuilt to do the cpu multiplayer?

I have a Tulip 486 board locked at 25 mhz, will check if this is possible for that

wow, cool

OMG PUT A HEAT SINK ON THAT QUICK!!!! I wouldn't clock that any higher with the bus up at 40 Mhz. Not unless you do some much better cooling. Those chips have been known to run at 160 Mhz stable but is the minor increase really worth the risk? A big portion of the speed increase you are getting is already in place by overclocking the bus. If you do clock it to 160 PLEASE get a really robust cooling solution going on there. Check out CPU Galaxy and his adventures with one of these up to 200 Mhz but he had to use a peltier cooler to pull that off.

My wife thinks you sound a bit like Christopher Walken :)

Doesn't the socket blaster do the multiplier tweak?

Reminds me of the original PC/AT. The motherboard had a 12MHz crystal but the schematics labelled it as 16MHz. Sure enough, a 16MHz crystal let it run just fine at 25% more speed. Then IBM noticed people were doing this and they added a speed check in the BIOS startup code so it would not boot if it was running at over 12MHz! So you needed to have a switched divider, putting out 12MHz for 10 seconds, then switching to 16MHz. Easy peasy, almost.

When the odd "586" cpus were released, I never understood the draw. Pentium was out and offered a much better architecture. But for this use case they are really great.

lol so cool! 🙂

>in previous videos "IBM PS/1 DX4! upgrade with more Cache and RAM. And I got the ancient vir..." aK6iLC4s4 video is gone :(

old pc magazine

xD lol push amd dx4 to limited and make this super faster lol oh dont forgot stick heatsink on it because she does get hotter at 3.4v or 3.5v just save yourself a headache in future ya knew ibm using tricky ideas putting resister on it got me laughing so tiny cant see it

When are you going to jump on the Commander X16 bandwagon?

Not that I want to defend IBM, but really, he didn't try to hide anything. Clickbait?