feipoa wrote:

As I recently discovered that the UMC UM8881 486 chipset works with double-sided 128 MB FPM memory sticks, it got me wondering - what's the maximum amount of memory which has been successfully installed (and functions) on a 486?

I have personally only tested up to 256 MB, but after noting success with 128 MB single memory sticks, I can't help but wonder if this undocumented UMC chipset will work with 384 or even 512 MB.

Can you please take photos of the board so that we can look up info about the board?

I wonder how long it would take a 486 to completely fill 512MB running balls out? And how that would translate into modern day PCs? I'd imagine on a high end i7 or Ryzen, the equivalent amount of RAM needed would be over a terabyte.

In theory the maximum amount of memory a 486 can address is 4GiB (4096MiB), without using PCI, as that would take up ~512MiB of that space.

DOS of any sort would be useless here, as even 98SE barely works over 512MiB. You'd have to use something like NT4, or maybe even NT5.

There is of course the main matter of the chipset, more importantly the memory controller as those were external. In theory you could make your own using some strange hackjob of an FPGA, but the effort and time needed to make a 486 use more memory than it should would be a waste.

An interesting question is to see how big of a PAE one could do on a Pentium Pro. Those can go up to 64GB, but I have never seen a board with a memory controller that could go that high.

My gut feel is that it may only support 4 banks, though if manual says it works with 2MB, 8MB, or 32MB in all 4 slots then it obviously has 8 so should take 4x128 modules.... however, there are sometimes other problems that stop it, like failure to map PCI expansion ROMS high enough etc.

The main issue is that in WT cache mode the cacheable area is 128 MB. (64 MB in write back mode)
So most memory will run uncached.

What I seemed to experience with uncachable memory in the past was... by the time your application needs that amount of RAM, the time is long past where the system will ever be fast, and it's made even more dog slow by swap file thrashing, so cached or not, more memory makes it faster. You put 128MB in a system that caches only 64, and will it slow down doom or quake under dos? No, because they don't use that much. You want to run a windows game when you've got your system so bogged down with other crap that the game can't load under 64MB, well then it's just gonna churn swapfile if you don't put more RAM in. I mean if you can, pick the system with more cachable area, but in general your slow CPU is the biggest problem by the time you are running something that huge to be outside the cache. There are edge cases.... like you can slap a K6-2 non plus into a TX mobo that only caches 64MB and show that it's slower than a MVP4 that caches 128, and slower still than sticking a +2 or +3 in any board where all the cache is on the CPU, but that's kinda beside the point. There's just not enough situations where a huge amount of RAM would be a benefit, where a 486 would not be the factor slowing it down the most.

I remember back in 1996-2002 that memory wasn't exactly a huge issue until Windows XP SP3. I had an old Packard Bell running Windows 95 on a Pentium 100Mhz with 16MB of RAM and it ran DOOM perfectly fine....like, from within Windows. When I got a new PC running Windows 98 on a 350MHz Pentium II, I included 128MB of PC-100 memory. I NEVER ran out of useable memory, even under heavy gaming. So when people build a retro gaming PC here and they brag about putting in 700+ MB, I have to wonder why they put so much memory in. Bragging rights? In my rebuild, I added a second stick for 256MB of RAM, and I STILL feel like that's FAR overkill for Windows 98 SE, even on a 600MHz Pentium III with a RIVA TNT2 32MB AGP card and dual Voodoo2 cards.

Windows XP ran on 256MB of memory well right up into SP2. SP3, however, killed that system's ability to run (Athlon XP 1.53GHz) smoothly. To run SP3 well, I had to upgrade to a full 2GB of DDR-400 during the rebuild, as well as re-capping the MB.

Why did I write any of this? Because even for DOS gaming, I couldn't imagine needing any more than 32MB of memory on a 486 DOS-based system. 64 at the highest end. Hell, my Windows 95 gaming system has 64MB and that feels like A LOT (read: a shit ton). Why would anyone put 128MB or 256MB of memory in a DOS system with a 486? Bragging rights? you do remember that DOS can't really multi-task, right?

32 is also the max for me regarding 486s, 64 on a pentium because you need two simm-modules and the 32s are usually the most common/cheapest.

I guess, folks like to "max" out memory on old systems because it is what would have been THE setup in those days - but unaffordable by commoners.

THE setup? I remember reading magazines about big gaming rigs that cost nearly $4,000 at the time, and I don't remember any of them in the Windows 98 era ever advertising over 256MB. Granted, I haven't seen ALL of the advertisements in ALL magazines ever put out in those years. But seriously, come on. On my retro system right now, running next to me, Resource Meter shows 89% Resources Free. That translates to only ~28MB of space used...out of 256MB. Even with only 128MB of memory, that's still 100MB for games to run on. And only a handful of the games from that era even used 100MB of HDD space for all files. The most demanding game I have on this system is Return to Castle Wolfenstein. And yes, the P3 600MHz and the TNT2 32MB card are seriously bottlenecked by the game, but it runs. In fact, I get just enough framerates to be able to play it with only a mild annoyance.

I just never saw the need to max out a system if you don't have a use for it. My 2010 gaming rig allows for 16GB of DDR3-1600 total. I ran with ONLY 8GB for YEARS with no issues whatsoever. I'm running 16GB DDR4-3200 on my current rig, but I'm also running 3 screens and the MB supports up to 64GB total of DDR4. I have this website up in a tab on Chrome, a Facebook tab, and Netflix app, as well as a few others. I'm using 6.8GB out of 16GB.

God, I wish I had today's Performance Tab on Task Manager back in Windows 98. I would love to see details about memory usage.

But I still stand by my opinion. For me, 32MB for Pentium 1 and Windows 95, 128MB for Pentium II/III and Windows 98, 1GB for Windows XP SP3, 4GB for Vista and 7, then 8GB for Windows 8/8.1/10.... unless you're doing video editing. Those guys have hardware needs WAY past gaming.

And oh yeah, I've never actually used a multi-core CPU with Windows XP. All my XP machines were single-core processors without Hyper-threading and I never really had much of a problem. But I see a lot of people doing XP retro systems using Core 2 Duos or Pentium Ds (I never had a Pentium-D). Does it really help? I can't STAND trying to run Vista/7/8/8.1/10 on a single-core CPU (my netbook has a single-core Atom running Windows 10 ... and it's rather slow).

Doesn't matter what machines were sold with.. People were still mesmerized by a machine that had excessive amounts of any spec (including ram) even if it was totally inconsequential to performance (or in reality with caching, detrimental). I knew a few guys who did nothing but play DOOM and fart around with Qbasic who were running 32-64 megs on 486 class machines running DOS and would boast about it, and this was when RAM was ridiculously expensive. [I also read often that 16MB was a standard configuration back then for 486 machines, but it wasn't, 8MB was high end, 16 was extremely expensive and didn't become common even on the high end until toward the end of the 486's reign (1993-1994). We dropped $3000 for a 486 33 with 8MB in ~'92.]

Same goes on today with people running 32 or more gigs and justify it because they make YouTube videos here and there in a non-professional environment that doesn't require the extra few minutes saved in rendering time. It just feels nice to buy that extra memory.

On the other end of the spectrum, there WERE use cases where obscene amounts of ram became very useful. CAD could chomp up a ton of memory and then slow to a crawl with disk reads, multi user Unix setups or Unix setups with virtual dos environments were around back in the 386-486 days and needed big memory.

On topic..

In theory (covered already) the 486 can address 4GB (2^32) if the motherboard supplied a memory controller that could handle it. In 1990 4GB of ram would have run you nearly half a million dollars though 😎

In reality, the most I've heard of is 256MB double sided. In practice the most I ever saw was 128Mb in giant file servers or a few Unix machines. Those numbers EXPLODED after 1995 when memory prices came down and the Pentium Pro hit the streets, just in time for fancy web servers.

My first PC circa 1993 was a 486DX33 and it came with 4MB ram.
I remember salesmen were excited because their demo computer on display had 24MB installed which was a total overkill at the time (1993).
However a little later 4MB Ram was just enough to play Rise of the Triad on my motherboard. A friend with his 386DX40 and 4MB Ram wasn't as lucky because his motherboard must have reserved bit more ram and ROTT didn't want to run reporting lack of memory by literally 1 or 2 KB. That was until we came across DOS/32a (replacement for dos4gw) which used a little less memory to run.

My current retro rig is based on PIII 500 and Asus P3B-F and has 768MB of registered ECC Ram installed. I picked up the memory on eBay for less than $10 delivered so to answer someones question: it's not for bragging rights but because it was dirt cheap. OS of choice is Windows Me with Dos mode enabled and windows 2000.

Vallenrod wrote:

My first PC circa 1993 was a 486DX33 and it came with 4MB ram. I remember salesmen were excited because their demo computer on d […]
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My first PC circa 1993 was a 486DX33 and it came with 4MB ram.
I remember salesmen were excited because their demo computer on display had 24MB installed which was a total overkill at the time (1993).
However a little later 4MB Ram was just enough to play Rise of the Triad on my motherboard.
A friend with his 386DX40 and 4MB Ram wasn't as lucky because his motherboard must have reserved bit more ram and ROTT didn't want to
run reporting lack of memory by literally 1 or 2 KB..

Funny, my 286 had got the same amount of memory installed (4MiB). ^^
24MiB was about the amount of memory I had got back in the days when I used to work with Windows 98.
My father, on the other hand, already had got installed 16MiB of RAM in his 386-40 back in the early to mid-90s..
Nowadays, PCs are usually having 16GiB (Gibibytes) of RAM. ;) I guess it depends on what we do with the PC.
DOS/W3.x software runs fine with 4MiB of RAM most of the time. Except for DOS4/GW games, maybe.
They want a little bit more.

feipoa wrote:

As I recently discovered that the UMC UM8881 486 chipset works with double-sided 128 MB FPM memory sticks, it got me wondering - what's the maximum amount of memory which has been successfully installed (and functions) on a 486?

I have personally only tested up to 256 MB, but after noting success with 128 MB single memory sticks, I can't help but wonder if this undocumented UMC chipset will work with 384 or even 512 MB.

You gonna load it down with RAM and install Windows 2000? You have me curious, for sure.

ugg... My 128mb simms cost me like $30 each. I'm not gonna dick with them. But that's 512mb for a 486. Do they even make larger simms?

elianda wrote:

The main issue is that in WT cache mode the cacheable area is 128 MB. (64 MB in write back mode)
So most memory will run uncached.

Yes, for a system with only 512 K of L2 cache. But for one with 1024K, WT will cache 256 MB. But for 256 MB, I could just use 4x64MB. The issue I have run into, though, is that when pushing the FSB speed, cache/RAM wait states, it is more beneficial to have less sticks, that is, 1x64 works better than 2x32 under such conditions. For the reason of module reduction is why I started testing 128 MB SIMMs.

On the MB-8433UUD with IBM 5x86c at 2x66 MHz, I seem to be able to get away with 1 ws for RAM if I use 1x64 MB. If I use 2x64 MB, I must use 2 WS for the system to stable to my satisfaction. I was hoping that 1x128 MB will let me get away with 1 ws. I was not expecting 128 MB sticks to work at all, in fact, and got me wondering if the UM8881 chipset could actually address all 512 MB. Unfortunately, I do not have that many sticks, but might be able to try out 128+128+64+64. As 256 MB would be the max cacheable, this experiment is really just for gross curiousity. Another issue I was wondering, though, is if using a 128 MB stick, is it possible that the memory test might read all 128 MB, but cannot actually write to it? That is, say it skips every other 1 MB, thus really only using 64 MB?

BitWrangler wrote:

What I seemed to experience with uncachable memory in the past was... by the time your application needs that amount of RAM, the time is long past where the system will ever be fast, and it's made even more dog slow by swap file thrashing, so cached or not, more memory makes it faster. You put 128MB in a system that caches only 64, and will it slow down doom or quake under dos? No, because they don't use that much. You want to run a windows game when you've got your system so bogged down with other crap that the game can't load under 64MB, well then it's just gonna churn swapfile if you don't put more RAM in. I mean if you can, pick the system with more cachable area, but in general your slow CPU is the biggest problem by the time you are running something that huge to be outside the cache. There are edge cases.... like you can slap a K6-2 non plus into a TX mobo that only caches 64MB and show that it's slower than a MVP4 that caches 128, and slower still than sticking a +2 or +3 in any board where all the cache is on the CPU, but that's kinda beside the point. There's just not enough situations where a huge amount of RAM would be a benefit, where a 486 would not be the factor slowing it down the most.

On the flip-side, if you put in 128 MB for a system which can cache only 64 MB, and you run a game which doesn't really need more than 64 MB, you'll really want to remove that extra 64 MB stick because I recall people saying that Windows 9x uses memory from the top down, meaning that the memory in the 64-128 MB range would be used first. If that is true, then it seems you'd want to be able to, on the fly, flip between using 0-64 MB and 0-128 MB.

FFXIhealer wrote:

I have to wonder why they put so much memory in. Bragging rights?

For some, perhaps bragging rights. For others, like myself, I like the feeling of a motherboard taken to its limits. There are also those who probably don't like seeing empty sockets and slots. From my own experience being an NT4 user in the 90's, 128 MB was far more ideal than 64 MB. I do try to setup the software on my retro systems to those which I used at the time, and I tended to use my systems well past their prime. The purpose of the thread, though, is not so much about practicality as for curiosity.

luckybob wrote:

ugg... My 128mb simms cost me like $30 each. I'm not gonna dick with them. But that's 512mb for a 486. Do they even make larger simms?

One user above says he's heard of 256 MB SIMMs, but I'm skeptical of their existence. Are there even 128 MB SIMMs with parity?
Do you have 3 or 4 128 MB SIMMs and a MB-8433UUD? If so, I'd be very interested in your results.

I have two "high end" 486 boards. Both VIP and UMC 8433 chipsets (iirc), one is a pc chips with no cache and the other has sockets for up to 1mb of cache, but i cannot for the life of me find jumper settings, and there are like 30 jumpers on that board, so just winging it is a non-starter.

my simms are edo/fpm and I never considered even attempting them in a 486.

Both motherboards are in cases and they are currently buried in a pile at the moment. I'd be happy to get them out for you though.

The first to attempt 512 MB on a 486 sounds like a novel enough cause to bring out the excavator!

feipoa wrote:

The first to attempt 512 MB on a 486 sounds like a novel enough cause to bring out the excavator!

In the name of vogons-science - do it.
512 would be interesting in a board like the R512, not a 486 though, which officially supports 2MB of cache... WriteThrough action time so to speak.
I do not know of a 486 with such juicy cache configuration but I guess there are many server boards which would fit the bill - maybe "Chips" could chime in here.

I thought 256k 512k or a meg didn't matter it was the tag RAM that defined cacheable area.