XMS 3.0 supposedly allows for allocation of up to 4GB of memory (https://en.wikipedia.org/wiki/Extended_ ... tion_(XMS)).

LIM EMS 4.0 supports up to 32MB, and all Dos/4GW programs support up to 32MB.

Unreal Mode programs can access 4GB. https://en.wikipedia.org/wiki/Unreal_mode

Windows could access the 4GB through Himem.sys.

Otherwise it could be made into a RAM drive...

Don't know how you would go about doing any of that, or the value... Compact Flash cards are fast enough as a drive. Windows XP itself only supports a max of 3GB.

A rough guide to 486 memory...
4MB Minimal amount to do "486ey" stuff really,
8MB yay, breathing room, required in a handful of cases.
16MB sweet spot, everything that runs at a satisfactory speed on 486 fits here.
32MB also nice, maybe a bit better for win98. DOS stuff that needs this is a slideshow.
64Mb probably optimum only for win98 stuff, you are setting your cache up right? in DOS you can ramdrive any game that runs okayish on 486
128MB dead end for 90% of 486 board cache configurations, stuff that needs this is incredibly slow on a 486, this was PIII era. Slideshow? You wish, it's a powerpoint presentation with long discussion of every slide.
256MB you are probably out of the cache now, Athlon and P4 era RAM size, your 486 is only twenty times too slow to run their proggies.
512MB Hah, you're a masochist right? Load time from fastest possible storage to fastest possible RAM is now counted in seconds for anything that needs this to fit. Execution time? take a long lunch.
1024MB Cue Freddy Mercury "Can't cache me now" even the unicorn boards have given up, win98 breaks, and your CPU is 50 times too slow for anything that needs this.
2048MB Plan a weekend break for anything you launch needing this to be nearly done when you get back. Never mind that anything needing 256MB up probably needs at least MMX, and you'll be missing one more architecture extension every step up from that.
4096MB dude, nothing has got better for the last 4 or 5 steps up, what makes you think this will be the one?

I'm aware there is no practical reason to go that high or anywhere even close. I chose 4 GB simply because it's the highest theoretically possible on a 32-bit x86 system. The only value in actually doing it is being able to say you did it. However, that alone can be quite a motivator. "Why" is usually the wrong question with absurd hack projects. 😀

My more realistic questions were:

1. Is expanding RAM (by some amount) using VLB realistically doable? Is it just like doing it via ISA, but with a wider, faster bus?

2. Has this ever been done? The fact ISA RAM cards exist seems to imply there was/is a market for adding RAM in places other than the RAM slots.

As far as I'm aware no one has attempted a VL bus memory expansion. In theory it should be possible, but there may be some roadblocks due to chipset and cache limitations. Since other hardware will take up memory address space, a complete 4Gb will not be obtainable.
Most VLB motherboard supported at least 64Mb of ram, some even claimed 128Mb and possibly beyond. Considering the speed of a 486 CPU, that is already a generous amount of ram.
My 486DX2 66 can just barely hit 62Mb/s transfer rate for its internal L1 cache. It would take over a minute to fill 4Gb of ram at those speeds. In reality, the transfer speed will be slower than this.
Dealing with datasets this large would be impractically slow on a 486. A single pass of memtest86 would take weeks if not months to complete.

TechnoFairyGirl wrote on 2024-08-09, 16:52:

I'm aware there is no practical reason to go that high or anywhere even close. I chose 4 GB simply because it's the highest theo […]
Show full quote

I'm aware there is no practical reason to go that high or anywhere even close. I chose 4 GB simply because it's the highest theoretically possible on a 32-bit x86 system. The only value in actually doing it is being able to say you did it. However, that alone can be quite a motivator. "Why" is usually the wrong question with absurd hack projects. 😀

My more realistic questions were:

1. Is expanding RAM (by some amount) using VLB realistically doable? Is it just like doing it via ISA, but with a wider, faster bus?

2. Has this ever been done? The fact ISA RAM cards exist seems to imply there was/is a market for adding RAM in places other than the RAM slots.

If my memory serves me right then...
Those ISA ram cards were more for XT & 286. going to 386 & higher the memory bus is more separate from the isa bus.
Though I have no idea if the VL bus has direct access to the memory bus, if yes, then I guess it would be possible, if no then you're SOL.

Ram in the trash? Ram I'm the trash? Not where I live. These ******$ here in NJ almost never throw anything out.

RAM in the trash is definitely a thing. Most of my local PC shops toss anything ddr2 or older into a trash bag for recycling. If you are on good terms with your local shop. It is possible to score some RAM for free, or at least at scrap value.

My job's IT department also throws out a lot of perfectly good hardware. Windows 7/8 era machines with 4/8 GB of RAM appear on the e-waste cart pretty regularly, with newer machines appearing occasionally as well. My best save so far has been a 10th gen i5 mini PC in perfect condition which currently serves as my HTPC. I also scored a Vortex86-based thin client with an ISA slot that, once populated with a suitable sound card, made a decent DOS gaming PC.

I’ve always found it confusing that VLB or PCI ram wasn’t a thing.

Buffalo memco actually made a card that plugged into the cpu socket to add extended ram, one would hope VL or PCI based ram would be easier.

The unfortunate issue is that it is very possible the memory controller pins off the north bridge don’t go there which would make it “non-standard “ ram.

If that were the case you would need to bond an ISA&PCI or ISA & VL slot to get the memory signals.

Sounds like fun

There have been some earlier discussions here on what the practical limits to memory expansion on the 486 were back in the day. But I won't go into detail again here. I'll make a few related points to the question:

There were likely just proprietary memory expansion slots in 486 like in 386 servers to achieve the higher specs these chips afforded. No one else cared. The 486 matured when RAM simply 1-4MB was hard to come by for the average person, except at the very end of it's life.

I believe SMP first appeared on the 486 for the x86. That could maybe make better use of more memory.

Likewise, recycled 486 systems were used to create the first beowulf cluster.

The 486 like the 386, was useful for its massively larger virtual memory capability. Perhaps useful in super-computer like situations of the day. But not so much for 1GB+ physical memory to a single program. That would have been difficult to realize in any computer spec then.

I don't believe there is any likely user of 486es back in the day that had 1GB or more memory. I think that would come during the pentium era. And more than 4GB, with the pentium pro. (obviously)

VLB probably was just consumer oriented. So I don't think anyone bothered with RAM expansion because enough expansion was available through simm sockets. I'd be pretty certain if this could be made, it would be pretty unique.

VL boards can certainly provide memory, like SVGA cards with linear framebuffer do. It's possible that some chipsets have built-in assumptions about where external memory should be allowed in the sub-16MB or sub-1MB spaces, which could cause a conflict. Hard to know without researching it.

One problem with making a VL memory board is that the bus is 5 volts. Modern memory types wouldn't be able to connect directly (nor FPGAs)

the3dfxdude wrote on 2024-08-09, 19:58:

VLB probably was just consumer oriented. So I don't think anyone bothered with RAM expansion because enough expansion was available through simm sockets. I'd be pretty certain if this could be made, it would be pretty unique.

That probably makes the most sense.

The performance issues (like the VLB memory not being cached, and requiring more wait states than onboard SIMMs) aside, it seems like there would be a narrow audience in 1993 to spend more than $2000 on RAM alone (for 64MB) and still want more, yet then want to skimp out with consumer VLB boards rather than buying a "proper" workstation or server system.

Weren't there some SMP systems from NCR in this era with a backplane design and capability for a huge memory expansion without resorting to VLB?

Is it for the reason of expanding beyond what was intended by the mobo manufacturer?

Keep in mind that every bus (PC buses anyway) provide access the uPs core function. Even to a large extent buses like a cartridge slot.

the3dfxdude wrote on 2024-08-09, 19:58:

I don't believe there is any likely user of 486es back in the day that had 1GB or more memory. I think that would come during the pentium era. And more than 4GB, with the pentium pro. (obviously)

I agree. If anyone needed and could afford more that much RAM, they would have been buying something other than x86.

akimmet wrote on 2024-08-09, 21:14:

the3dfxdude wrote on 2024-08-09, 19:58:

I don't believe there is any likely user of 486es back in the day that had 1GB or more memory. I think that would come during the pentium era. And more than 4GB, with the pentium pro. (obviously)

I agree. If anyone needed and could afford more that much RAM, they would have been buying something other than x86.

What would be the most logical use of a really beefy x86 server back then? NetWare?

jakethompson1 wrote on 2024-08-09, 21:19:

What would be the most logical use of a really beefy x86 server back then? NetWare?

Windows NT 3.51 also was a big thing for beefy x86 servers.

jakethompson1 wrote on 2024-08-09, 21:19:

What would be the most logical use of a really beefy x86 server back then? NetWare?

Most likely a file server. Netware, or Windows NT. A Database server running Windows NT, or UNIX of some kind would also be very likely.

akimmet wrote on 2024-08-09, 23:17:

jakethompson1 wrote on 2024-08-09, 21:19:

What would be the most logical use of a really beefy x86 server back then? NetWare?

Most likely a file server. Netware, or Windows NT. A Database server running Windows NT, or UNIX of some kind would also be very likely.

File server makes sense, and I believe for a while Xenix was actually the most popular Unix by number of seats. But I think it was more associated with point of sale systems at retail stores than big databases. You'd think the types who were running up against the maximum supported memory for an x86 chipset would be more likely to run the database on a VAX or a Sun system back then, especially before the Pentium Pro.

It wasn't that uncommon to see some small businesses save a few bucks by running their database on a PC running SCO Unixware/Xenix or Solaris for x86.
Sun and DEC only made business sense once uptime requirements and service contracts are taken into account.