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Restoring a small form factor 486

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First post, by kaputnik

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A couple of months ago, I was involved in transferring a passenger ferry built in the late nineties to the Mediterranean. In the phone exchange room onboard, I found this lovely little 486 computer collecting dust:

FiWtFPC.jpg

Would guess it's been used for the PBX software now running on a much more modern replacement, and taken out of commission years ago. Luckily, no one had bothered to remove it from the PBX rack and scrap it.

There was of course no way for me to get a broken computer into the handover exclusion list, would just look extremely strange if I tried, but figured no one would mind if I spared the new owners some e-waste handling. Stowed the 486 together with my personal belongings in a container that was sent back home. It arrived last week, and now I'm back at home starting my first adventure in 486 land since the nineties, trying to bring it back to life.

I did open up the case to take a peek inside before going home, and one of the first things I noticed was the creative use of - I shit you not - a toothbrush handle as heat sink retention device:

ZpxsRDI.jpg

Also, the CPU fan was mounted upside down, the rotor jammed by the heatsink. The case fan isn't in the best shape either. Can imagine they had some overheating problems. Maybe that's the whole reason they replaced the 486?

2022-05-12:

Today's mission was removing the network hub attached with extremely strong double sided tape on top, and taking everything apart for cleaning and inspection. There were no more real surprises. Found a broken reset button wire, fragments of the original heat sink retention clips, and lots of dust. There's also some light oxidation on the ISA edge connectors that might have to be dealt with.

The hardware is consisting of:

* IEI SSC-5X86H Ver C ISA single board computer
* Am486 DX4 100V16BGC CPU
* BP-4S ver B1, four slot ISA backplane
* 2x4 MB FPM RAM
* Cirrus Logic CL-GD5429 ISA graphics adapter
* 3Com Etherlink III ISA NIC
* Startech TC210 additional ISA LPT/serial port controller
* 1,2GB Seagate Medalist HDD
* Floppy drive
* And of course also the small form factor industrial case, with built-in PSU.

BWyuoX9.jpg

Will replace the TC210 board with a sound card, haven't decided which yet. Got a spare ESS Audiodrive that might fit the bill. If the HDD is broken or too noisy, it'll be replaced too. Time will tell.

If you look closely, you can see how the fan is mounted the wrong way on the CPU heatsink.

zVTAiNM.png

Repaired the broken reset button cable, soldered together an adapter/splitter for the connectors used with modern fans, and started assembling the computer again. Started up the PSU briefly, seems to work as intended. Installed a new Noctua case fan. Yes, it's grey, not the regular brown/beige color scheme. Matches the case color perfectly. It's more or less inaudible with a low noise adapter. Also modelled and 3D printed a shim that goes between the fan and case, as a fix for a design miss that would have allowed hot air to circulate back into the case. Preferred this way over widening the fan's mounting holes.

And that's all I had time for right now. Will update as the project progresses 😀

2022-05-13:

Continued the project this morning.

Modelled and 3D-printed new clips for the CPU heatsink, scrounged up a new 40 mm fan and soldered on a connector. Finished assembling the computer the way it was before taking it apart, except for the additional serial port controller that was left out. Installed rubber feet on the case.

GsHT0iu.png

Plugged it in, tried booting it up, aaand... it's dead. There's a very short beep from the onboard buzzer, and it seems to respond to the reset button, giving off another short beep after pressing it, but nothing is displayed on the monitor. Double checked all jumpers on the SBC since the computer obviously has been messed with by someone without the right knowhow, but everything seems to be in order.

Some suspects:

* Fried CPU. As mentioned earlier, the original CPU fan was completely stuck, and it would also surprise me if the old chassis fan worked. Got no other 486 class CPU to test with though.

* The Dallas RTC. The built in battery is certainly flat after more than 20 years. Experienced computers with flat CMOS batteries behaving very oddly, freezing in the middle of POST etc, but never apperaring completely dead though.

* RAM. Haven't dealt a lot with 72-pin SIMMs the last decades, but in my experience those low insertion force sockets are less reliable than modern ones. Might just be a question of badly seated SIMMs.

* The graphics adapter. Never heard of one of those going bad, but guess it's possible. Sadly, it's the only ISA graphics adapter I have.

An ISA POST card could probably be useful for troubleshooting this. Might order or build one, guess that's something every retro enthusiast should have anyways. Only got a PCI one now.

Also, the HDD sounds like a jet plane. Might be bad bearings, but could be normal too, those old HDDs can be quite noisy. I'll replace it anyhow, once I get the computer back to life, after checking what's on it.

To be continued.... 😀

2022-05-14:

While the CPU is my prime suspect, I decided to begin with the things I could do something about right now. Removed RAM, cleaned connectors, and reseated it again. Also tried both SIMMs alone in slot 1. Did not help.

Then it was the Dallas RTC's turn. Started by desoldering it and installing a DIP socket instead. I never really liked the standard mod, where you leave the old battery in, so decided to completely remove the old battery and potting compound. Got a few spare non potted DS12885:s and xtals, so took a gamble trying to use heat to soften the compound. It worked above anticipation.

Set the hot air reworking station to 200 deg C. After some heating, the outer plastic shell easily peeled off. Dug into the potting compound, that could easily be carved with a hobby knife and a small chisel when heated. Laid the battery and xtal bare, desoldered their connections, and could remove them completely unscathed.

iQf7zLC.jpg

Removed the rest of the potting compound, reinstalled the xtal, and added a CR2032 battery holder. Installed the modded RTC module in the 486. No cigar, it still shows no life signs.

3iXyeaF.jpg

Tested the RTC module in my P233MMX rig, just to make sure I didn't add another problem. It works perfectly.

While the datasheet states a maximum reflow temperature of 260 deg C, I'm not sure how the DS12885 reacts to being heated to 200 deg C for the extended time the potting compound removal takes. I've never seen anyone mentioning applying heat when doing this mod before, but I can't possibly be the first one to get that idea either. Maybe it's never recommended simply because it's not a good idea? Don't try it unless you have a spare RTC.

Also tested the ISA graphics adapter in another computer, and it works fine.

So, anyhow, guess I'm stuck here until I've sourced a new CPU or ISA POST card, to do further testing with. To be continued then 😀

2022-05-23:

Had a chat with a guy who was the electro-technical officer on the ship before it went on an earlier three year charter in the Mediterranean a few years ago. Before that, when operating on more northern latitudes, the 486 was definitely working. He also insisted that he was completely blameless when we came to the toothbrush handle 😁 So, we got a high end 486, that's been running without adequate cooling in a small room stuffed with other heat generating electrical equipment, with Mediterranean summer heat on top of that. Getting more and more certain the CPU is fried...

Looks like I might have a replacement DX33 or DX2 66 in the pipe. Not as cool as the original DX4 100, which also is the top of the line variant with 16k of WB L1 cache, but in the end it doesn't really matter. Got a P233MMX rig if I need performance.

Now I'm just waiting for the guy with the replacement CPUs to find them, hope he does soon 😀

2022-06-19:

The replacement CPUs has finally been found, seems like it's going to be a DX33 😀 The project hasn't been standing completely still while waiting though. Cleaned up an ESS Audiodrive (ES1869), soldered in pins on the wavetable header, and ordered a Dreamblaster S2 for it.

Also repaired the broken door in the floppy drive. Used a long header pin and reshaped the spring from a cigarette lighter for the closing mechanism. Was a bit fiddly, but the end result works great. As good as new:

N033omZ.png

Hopefully getting that CPU any day soon. Can't wait to finally be able to finish this project, given of course that the CPU really is the problem 😁

2022-06-23:

As usual in the summer, I'm quite busy with outdoors stuff. Spared a little time this morning to sort the mess that was the IDE and floppy cables though, the weather outside wasn't optimal anyways. I did have a spare 40 pin IDC connector, but for the floppy cable, I had to reuse the old one. It's a lot harder than one might think to remove an IDC connector from the cable without breaking those small plastic tabs holding it together.

Customized the cables for this particular machine. Pressed the connectors in a watchmaker's vise with plastic jaws, got no special tool for it. Quite satisfied with the result, before and after:

XMRSCr9.png

Hopefully this will give the airflow in the case an improvement, to what extent it's needed with the new DX33 CPU, which I still haven't received by the way. It's never a bad idea to keep the HDD as well cooled as possible though.

2022-06-29:

So, finally got the new CPU today! Unpacked and installed it, and went through the jumpers before plugging the SBC in. Turned out there was no jumper setting for 5V CPU voltage. Crap. Should of course have checked that before getting a 5V CPU. Contemplated the fiasco for a little while, and then went on and installed the SBC with jumpers set to 3.45V just for the hell of it. What could go wrong? Powered it on, and after a few seconds there was a beep! A few more seconds later, and the POST screen showed up on the monitor 😁

yAejaov.png

Really surprised the CPU works with a 30% undervoltage, but well, I'm not complaining. Guess that also proved my theory correct, the original CPU is dead. Almost hoped it was something else, that CPU was kind of cool. Will also measure what voltage the CPU actually receives at some point, never know if there's some identification going on, and the CPU actually gets 5 volts after all.

9pTCKoo.png

Booted up the original hard drive. It had some version of DOS installed, and auto launched the PBX software. Of course I had no manual, and there were no onscreen instructions. Tried to type HELP in the command prompt, which only threw me an error message. Quickly found out that the F keys were mapped to various debug commands etc. Tried all of them, and soon found that F12 actually issued the HELP command, but that no online help seems to be installed. Decided to explore the HDD at a later time, and go on with the new installation.

The only suitable IDE drive I had available acted up - for some reason it showed up as slave in BIOS even though it was jumpered as single drive/master, tried three different cables - so installed a 2GB CF card in a CF to IDE adapter instead. Installed DOS 6.22, Norton Commander, and WFW 3.11 the good old way, from floppies. Easy enough to make installation media using my P233MMX equipped with both Gotek and regular floppy drive. Kind of nostalgic hearing those floppy drives for hours, and keeping fingers crossed that no floppy is bad, interrupting the setup 😁

Yes, I know I could just have transferred the setup files to the CF card using a card reader, but where's the fun in that? Should probably get another Gotek at some point though, that can be installed temporary when doing this kind of stuff.

Noticed that the SBC sagged a little bit, probably another sad result of that toothbrush handle affair. The SBC is just a little bit too short to reach the original expansion card supports, but was easy enough to model a custom support and 3D print, to straighten the SBC up. With some luck, it permanently reverses the sag over time.

486 DX33 isn't supposed to require a heatsink or a fan afaik, so skipped them, but checked the temperature. Almost 50 deg C under load, a little bit too high in my opinion. The case is small too, the ventilation is probably not the best. Might install that heatsink and fan after all.

Will wait with that until tomorrow though, it's getting late. There's also cable management to do, a sound card to install, etc 😀

2022-06-30:

Today has been mostly about figuring out how to do diagnostics in DOS 6.22 on an old 486. Hit me that I never had any real problems with my other retro builds before, they've basically just worked.

While installing and testing software, I got the feeling the computer was a lot slower than it should be. As far as I can remember, the 486 DX33 my family had in the nineties was a whole lot snappier. Doom runs at maybe 2-3 FPS on this computer. Also, the network is painfully slow, only get transfer speeds of ~150 kB/s.

Ran Speedsys. The benchmark result is rock bottom, more like a 386 than a 486:

8SMQ3iw.png

Noticed the summary screen displayed after POST states that there's no cache. The CPU Internal Cache option in BIOS is enabled. Got no idea if the summary screen refers to internal or external cache. Will have to study the SBC closer at some point, see if there are any cache chips on it. Didn't see anything at a glance, but then again, the small form factor SBC generally seem to use smaller packages when possible. Everything doesn't look like you might expect. Also might be an idea to read up on 486 cache architecture, instead of just assuming it's identical to Pentium ditto.

YxAamCk.png

Seems like there are no BIOS images for the SBC available online. Even tried mailing the manufacturer asking about it in preparation a month ago, but unsurprisingly they didn't bother to reply. Decided to dump the installed BIOS just in case. Took a while, but managed to find a version of awdflash that was compatible. Dumped a few copies of the BIOS, compared the images by content to verify the dumps were identical, and backed them up.

Installed the ESS Audiodrive (ES1869) based sound card. Worked perfectly out of the box. Tried plugging in the Dreamblaster S2 and boot the computer, but this made the PSU's overcurrent protection trip. Couldn't believe a brand new Dreamblaster was at fault, so began with the basics, checking the Audiodrive etc. The header pinout looks strange, the ground connections doesn't match the Dreamblaster's ditto at all as far as I can see. Actually looks like that 26 pin header is something else than a wavetable header entirely. Will have to find documentation and get this sorted at some point. Removed the Dreamblaster for now, hope it survived...

Also, the jumper headers on the CF to IDE adapter are coming dangerously close to the case side cover when it's closed. Lined the cover with electrical tape to be on the safe side.

2022-06-30, session 2:

Read up some on different 486 CPU models and cache. One of the CPU lists referenced the designations "&E" and "&EW" for WT and WB cache respectively. Seemed to remember those from the SBC manual, and had another look in the CPU jumper settings table. Sure enough, they're there. Jumpered the SBC for Intel DX4 &E instead of &EW to at least match the WT cache on the DX33, and now it looks a lot better in Speedsys, the benchmark is what you'd expect from a DX33:

xQKoAcE.png

Doom runs like I remember it, Windows feels a lot snappier, and network speeds come close to 500 kB/s. The post-POST summary still says no cache installed though, must refer to L2 😀

Thought those designations was some kind of print error yesterday, wouldn't be the first time in a mobo manual probably translated from Chinese. Now I know better, first adventure in 486 land since the nineties as mentioned 😁

2022-07-01:

Getting close to regarding this project as largely finished. There seems to be no possibilities to sort the L2 cache question, guess I'll have to live without it. The computer performs very much like I remember the family's DX33 machine did in the nineties, and it closely matches the reference value for a DX33 in the benchmark apps I've tried. Maybe L2 isn't all that important on a 486 after all? Or their reference DX33s didn't have any L2 cache either. Perhaps it was regarded as a luxury back then?

Found this page about the SSC-5X86H SBC. It states that the SBC has 128 kB of L2. The warranty stickers suggest that my card is somewhat older, May 97 and November 98 respectively. Maybe they added onboard L2 in a later revision or something. Also, mine is called "ver: C" while theirs is "ver: 3.0". Compared to their pics however, there are no chips on their card that's not present on mine. Except for the version designation, the cards looks identical. Would be interesting to know how/where they got that number, and perhaps ask them to dump the BIOS in case it's newer than mine, but given the current situation in Ukraine, it's of course completely out of question to bother them with trivialities like that.

Did some RAM tweaking in BIOS, memory bandwidth is now close to 100 MB/s, up from ~60MB/s:

D04ZkWa.png

As for the sound card, I'm now pretty sure what I first assumed was a wavetable header without any research is something else entirely. Would be interesting to find out what at some point. Will probably just order another Audiodrive card with wavetable header to replace the one installed now, they're still not prohibitively expensive.

Ran the Quake demo loop for half an hour or so, to stress the CPU and see where the temperature would end up with the case closed. This time the CPU only reached 35 deg C. Assuming the airflow around itimproves a lot with the side cover on. Will just leave it as it is, passively cooled with only a heatsink. No need for a fan.

Noticed the "Boot up system speed" option in BIOS, and googled around some. Apparently it's a software equivalent of the turbo button found on many older systems. There were also indications that the function could be toggled on the fly with a keyboard combination on some motherboards. Turned out my SBC can do it with ctrl alt + and ctrl alt - respectively. Quite cool feature 😀 No idea what it does under the hood, the CPU still seems to run at 33 MHz, L1 cache isn't disabled, but the computer is definitely slower, and memory throughput goes way down. Yet another Speedsys screenshot:

spa8FB7.png

So, guess that concludes the build log, or whatever you're supposed to call this. There are a few small things left to do at some point:

* Get a new Audiodrive card with wavetable header.
* Explore the original hard drive thoroughly.
* Explore the BIOS dump:
- Check if there are any interesting disabled options to reenable.
- Patch the Y2k bug that Speedsys reports if possible.
- Patch HDD size limits if possible.
* Build a programmer adapter for the PLCC BIOS chip and source another chip or two for experiments with patched images.
* Maybe replace the external screws on the case with countersunk ones for a cleaner look.
* Research if it's possible to add L2 cache somehow.

A list of the final hardware might be in order:

* Mobo: IEI SSC-5X86H Ver C ISA single board computer
* Backplane: BP-4S ver B1, four slot ISA
* CPU: Intel 486 DX33
* RAM: 2x4 MB FPM
* Graphics: Cirrus Logic CL-GD5429
* NIC: 3Com Etherlink III
* Sound: ESS Audiodrive (ES1869)
* Storage: 2GB 50x CF card in CF-IDE adapter, 3.5" floppy drive
* Case: Unknown small form factor industrial type

And of course a couple of pics of the computer in all its newfound glory:

yl287qd.png

EKfl3ko.png

Thanks for reading 😀

Last edited by kaputnik on 2022-07-02, 09:00. Edited 17 times in total.

Reply 2 of 27, by Hezus

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That's a nice system and a nice thread! Good read 😀

A single beep on start up should be normal, so can't say for sure that the CPU is dead. Often you would get a specific beep code for CPU issues. Take off the heat sink and feel if the CPU runs hot at all.

Is the keyboard responding with a numlock light?

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Reply 3 of 27, by kaputnik

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chinny22 wrote on 2022-05-15, 19:45:

Nice little 486 with great backstory,
good luck!

Thanks 😀 Hoping it's the CPU, that would be an easily fixable problem. They don't seem to be all that expensive either, even on Ebay.

Hezus wrote on 2022-05-15, 20:46:

That's a nice system and a nice thread! Good read 😀

A single beep on start up should be normal, so can't say for sure that the CPU is dead. Often you would get a specific beep code for CPU issues. Take off the heat sink and feel if the CPU runs hot at all.

Is the keyboard responding with a numlock light?

Thanks 😀

Oh, it's an extremely short beep, we're talking milliseconds, almost immediately after power on. If I were to guess, it's just the buzzer reacting to the circuitry becoming energized. Like the DC pop when you plug in headphones/speakers or something.

The CPU temp slowly rises to and stays at ~33 deg C after being powered on for ~10 mins without heatsink. Assuming you could expect something way higher from a fully working CPU even very early in the boot sequence? The rest of the SBC is just about the same temp too, might just be the CPU being warmed up by the peripheral components.

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Good call, should have thought of doing that test myself 😀 Tried all the lock keys, the keyboard doesn't respond to any of them.

This also made me remember an old S7 mobo with busted keyboard controller, that would hang on keyboard initialization, before outputting anything to the monitor. It behaved very much the same way. Also a possibility. Wouldn't surprise me at all if this someone who installed the CPU fan upside down and used a toothbrush handle for heat sink retention also hotplugged PS/2 keyboards without second thought 😜

Reply 4 of 27, by Hezus

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You could check the voltage on the VRM. I've seen a few examples of those getting worn out over time. According to your SBCs manual, it should read 3.3 or 3.45 volts (based on jumper settings).

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Reply 5 of 27, by kaputnik

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Hezus wrote on 2022-05-16, 14:53:

You could check the voltage on the VRM. I've seen a few examples of those getting worn out over time. According to your SBCs manual, it should read 3.3 or 3.45 volts (based on jumper settings).

Voltage looks good, measured to 3.295VDC between a VCC pin on the CPU socket and ground. It's also remarkably stable given the ancient and quite basic looking PSU. The board is jumpered to 3.3V.

Reply 6 of 27, by kaputnik

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So, got this baby up and running, it was the CPU 😀 Working on configuration and ironing out the details now.

A couple of questions have arisen:

- How much performance does external cache give a 486? Got the internal cache working, and the computer now performs as I remember the family's 486 DX33 did in the nineties. POST reports that there's no cache installed, assuming that refers to external cache. Would external cache give any substantial further boost?

- General consensus seems to be that the 486 DX33 will do fine without heatsink or fan. Personally I think it runs a little bit too hot, and in my opinion cooling is never wrong. However, there's no way to squeeze in anything but a small heatsink and a wailing 40mm fan in this particular rig. Got the heatsink on without fan now, the temp lands at ~50 deg C under load. What's your opinion on DX33 cooling? And what temperature would you deem acceptable?

Reply 8 of 27, by kaputnik

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maxtherabbit wrote on 2022-06-30, 13:41:

I run my DX33 with no cooling at all and it's fine.

L2 cache makes a BIG difference

Would it be possible to to specify "big difference"? Is it 5%? 10%? 25%?

You know how hardware folks are. Don't know how many reviews I've read where the object is said to completely obliterate the competition, but when you get to the actual numbers, you understand it's just a question of a few percent. I'd rather have the numbers when it comes to things like this 😁

Reply 9 of 27, by Toriessian

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kaputnik wrote on 2022-06-30, 16:15:

Would it be possible to to specify "big difference"? Is it 5%? 10%? 25%?

Disabling the cache on my old 486/DX2 66 was how I made it run at 386 speeds. I'd bet thats your culprit on your speed issues.
If you look at some of the old DOS game guides, you'll see disabling the cache as a recommended step on some games to slow them down.

Also hi all 😁

Reply 10 of 27, by H3nrik V!

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Toriessian wrote on 2022-06-30, 18:13:
Disabling the cache on my old 486/DX2 66 was how I made it run at 386 speeds. I'd bet thats your culprit on your speed issues. I […]
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kaputnik wrote on 2022-06-30, 16:15:

Would it be possible to to specify "big difference"? Is it 5%? 10%? 25%?

Disabling the cache on my old 486/DX2 66 was how I made it run at 386 speeds. I'd bet thats your culprit on your speed issues.
If you look at some of the old DOS game guides, you'll see disabling the cache as a recommended step on some games to slow them down.

Also hi all 😁

That sounds more like L1 cache disabling to me, though ...

Please use the "quote" option if asking questions to what I write - it will really up the chances of me noticing 😀

Reply 11 of 27, by Toriessian

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H3nrik V! wrote on 2022-06-30, 20:18:

That sounds more like L1 cache disabling to me, though ...

Yeah you might be right. I'm recalling a jumper on some boards to set the cache size. Maybe that jumper is just missing?

Reply 12 of 27, by kaputnik

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Toriessian wrote on 2022-06-30, 18:13:

Disabling the cache on my old 486/DX2 66 was how I made it run at 386 speeds. I'd bet thats your culprit on your speed issues.
If you look at some of the old DOS game guides, you'll see disabling the cache as a recommended step on some games to slow them down.

Also hi all 😁

Toriessian wrote on 2022-06-30, 21:30:
H3nrik V! wrote on 2022-06-30, 20:18:

That sounds more like L1 cache disabling to me, though ...

Yeah you might be right. I'm recalling a jumper on some boards to set the cache size. Maybe that jumper is just missing?

Yeah, L1 cache disabled by setting the CPU jumpers for WB cache equipped was the culprit before, that's sorted though. The last Speedsys result is in line with what one could expect from a DX33.

Wondered what further performance increase one could expect from L2 cache, which I believe my board isn't equipped with, or at least not enabled if present. I've of course read up on what every available jumper on the board does, there's nothing cache related 😀

Also tightened up the memory timings a bit now, using the "Fastest" setting in BIOS instead of the "Normal" default setting. No idea what that means in reality though, love when they use arbitrary designations like that... Speedsys reports 98.7 MB/s memory bandwidth now at least.

Reply 13 of 27, by jakethompson1

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kaputnik wrote on 2022-06-30, 21:58:

Wondered what further performance increase one could expect from L2 cache, which I believe my board isn't equipped with, or at least not enabled if present. I've of course read up on what every available jumper on the board does, there's nothing cache related 😀

Also tightened up the memory timings a bit now, using the "Fastest" setting in BIOS instead of the "Normal" default setting. No idea what that means in reality though, love when they use arbitrary designations like that... Speedsys reports 98.7 MB/s memory bandwidth now at least.

Indeed your board doesn't have an L2 cache or sockets for one that I would see. It would be pretty obvious as it would be nine DIP chips.

Here is the datasheet for your chipset: http://66.113.161.23/~mR_Slug/pub/datasheets/ … ALi/M1489-2.pdf
Looks like on page 95 it gets into what fast/fastest/etc. means. And in the BIOS guide starting on page 141 it starts giving recommended settings for different CPU speeds. Looks like this chipset supports EDO RAM, so you'll have to pull the RAM sticks and look up the numbers on the chips to see if they are EDO, and make sure you are taking advantage of that if so.

Since you have no L2 or any option for one, one upgrade would be from a DX-33 which has 8K of write-through internal cache to a different CPU with 16K of write-back cache, such as an Am5x86. But that would be partly reverting the downgrade to the DX-33, I guess.

Reply 14 of 27, by jakethompson1

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That datasheet actually seems to go into voluminous detail about EDO RAM. The usual consensus seems to be that 486 chipsets either don't support EDO at all or don't take maximum advantage of it. On page 95 that datasheet seems to claim it supports CP+5-1-1-1 and CP+1-1-1-1 read timing for page misses and hits, and on page 43 it looks like the check point can be cranked as short as "T1 end". So would that be 6-1-1-1 and 2-1-1-1 timing for RAM access depending on whether the access is within the same page?

Reply 15 of 27, by kaputnik

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jakethompson1 wrote on 2022-07-03, 00:28:
Indeed your board doesn't have an L2 cache or sockets for one that I would see. It would be pretty obvious as it would be nine D […]
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Indeed your board doesn't have an L2 cache or sockets for one that I would see. It would be pretty obvious as it would be nine DIP chips.

Here is the datasheet for your chipset: http://66.113.161.23/~mR_Slug/pub/datasheets/ … ALi/M1489-2.pdf
Looks like on page 95 it gets into what fast/fastest/etc. means. And in the BIOS guide starting on page 141 it starts giving recommended settings for different CPU speeds. Looks like this chipset supports EDO RAM, so you'll have to pull the RAM sticks and look up the numbers on the chips to see if they are EDO, and make sure you are taking advantage of that if so.

Since you have no L2 or any option for one, one upgrade would be from a DX-33 which has 8K of write-through internal cache to a different CPU with 16K of write-back cache, such as an Am5x86. But that would be partly reverting the downgrade to the DX-33, I guess.

jakethompson1 wrote on 2022-07-03, 00:37:

That datasheet actually seems to go into voluminous detail about EDO RAM. The usual consensus seems to be that 486 chipsets either don't support EDO at all or don't take maximum advantage of it. On page 95 that datasheet seems to claim it supports CP+5-1-1-1 and CP+1-1-1-1 read timing for page misses and hits, and on page 43 it looks like the check point can be cranked as short as "T1 end". So would that be 6-1-1-1 and 2-1-1-1 timing for RAM access depending on whether the access is within the same page?

Yea, DIP packages is what one would look for on a regular 486 board. Couldn't just rule out the possibility that they've used some miniaturized SMD version etc immediately though. Everything might not necessarily look like one might expect. After all, everything had to be squeezed in on a half size ISA board, and it's designed and manufactured years after most 486 boards.

That datasheet is really a wealth of information. Never occurred to me that something like it might be available 😀

In the end however, it's mostly a question of exploring possibilities. Got a P233MMX machine which can be tuned in very finely grained steps if I need performance in the region of an AM5x86 with 16kB WB. Trying to keep the number of retro rigs to an absolute minimum, and the 486 already felt somewhat redundant. Since it's so small, I couldn't resist this time though. Now I'm rather trying to find out how slow it can go, it's down to 2.5 Speedsys points using the soft turbo function (ctrl alt -) and disabling L1 cache with icd.exe now. The P233MMX bottoms out at ~12 points set to 100 MHz and all TR12 options disabled iirc. Makes the 486 less redundant 😀

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While I'm at it, a question for the experienced 486 users. Seems to be a lot of hate towards ISA graphics in 486 systems due to the poor performance compared to VLB or PCI. But when will the limited ISA bus bandwidth really start to matter? I mean, it's not like a DX33 will be able to run anything at playable framerates in 640x480 with higher bit depths or something anyways. Most of it will be 320x240 in 8 bit color, and for that, ISA graphics will suffice, right?

Reply 16 of 27, by OSkar000

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Some notes from the former owner of the DX33 😀

The cpu is from my Compaq Prosignia that I upgraded to a DX2 66 a while ago. Nice to see that it gets some more life out of it instead of filling my desk drawers.

ISA graphics is limiting in newer games on a 486 but if you stay away from SVGA titles its not a problem. The DX2 66 I have is limited to ISA/EISA and its currently equipped with a Cirrus Logic 5429 ISA, the same as you have. Running Windows isn't a problem if you have the right drivers and there are lots of games that isn't limited to the performance of the ISA bus.

A DX2 66 with VLB or PCI graphics is a much faster machine when it comes to newer games, but those mostly runs just fine on a Pentium or even newer systems.

Reply 17 of 27, by kaputnik

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OSkar000 wrote on 2022-07-04, 19:34:
Some notes from the former owner of the DX33 :) […]
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Some notes from the former owner of the DX33 😀

The cpu is from my Compaq Prosignia that I upgraded to a DX2 66 a while ago. Nice to see that it gets some more life out of it instead of filling my desk drawers.

ISA graphics is limiting in newer games on a 486 but if you stay away from SVGA titles its not a problem. The DX2 66 I have is limited to ISA/EISA and its currently equipped with a Cirrus Logic 5429 ISA, the same as you have. Running Windows isn't a problem if you have the right drivers and there are lots of games that isn't limited to the performance of the ISA bus.

A DX2 66 with VLB or PCI graphics is a much faster machine when it comes to newer games, but those mostly runs just fine on a Pentium or even newer systems.

Heya dude 😁

Yea, starting to reach the same conclusion. Windows feels snappy enough with the specific 542x drivers. Got the P233MMX for any games that needs a faster 486 and m0re bandwidth for the graphics. The DX33 and the CL5429 might be more or less optimal in this build. Also having thoughts of wiring up an external switch for toggling FSB speed between 25 and 33MHz.

Hopefully I'll get the opportunity to send you those 808x chips tomorrow btw 😀

Reply 19 of 27, by kaputnik

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keenerb wrote on 2022-07-04, 20:49:

For what it's worth I have switched over to sbc systems exclusively for my retro computing, and I have yet to see a 486 sbc with L2 cache, out of about a dozen I have gathered over the years.

Ah, well, no need to grieve at not having any L2 cache on my board then at least 😀

Can see why you did that switch btw, really started liking the SBC concept while working with this rig. Incredibly convenient, small desktop footprint.

Last edited by kaputnik on 2022-07-04, 23:00. Edited 2 times in total.