Socket 3 motherboards come in many flavors:
ISA only, VLB (many prefer this and consider it to be the standard), and PCI (for a taste of the future).

BUS speed is 33MHz or 40MHz. Some can go lower, some can go higher.

DX2 defaults to a 2x multiplier, so if you have an old board compatible with the original 486, you put the DX2 in and you get twice the speed!

Not all motherboards let you tweak the multiplier and not all chips support it. It's usually either 2x or 3x.

If you want to experiment with many CPUs, get a board compatible with 3.3v CPUs. Older ones are only compatible with 5v CPUs (DX, DX2).

Intel's DX4 @100MHz defaults to a 3x multiplier and runs at 3.3v.

Faster CPUs like the Am5x86 or IBM/Cyrix 5x86 can push things even further.

The Am5x86 runs at 133MHz (33x4) and can be easily overclocked to 160MHz (4x40). It's the most common fast processor for Socket 3. Go for this one if you don't want to spend a lot of money and get the fastest 486.

The Cyrix 5x86 is almost a Pentium but not fully. It's a very interesting chip though.

There's also the Pentium OverDrive but it makes more sense to get a Socket 5/7 system if you want to go for a Pentium.

Some people prefer a DX2 VLB build, and others go for a PCI DX4 or 5x86... it's your choice!
PCI certainly makes things easier as PCI video cards are cheaper and readily available.

That's very helpful.

In addition to socket 3 stuff, I'm seeing some boards that have 25mhz 5v 486 CPUs, stuff by micronics for instance. Is this socket 1? Do these have similar upgrade paths or not so much?

tauro wrote on 2024-07-05, 17:50:

Some people prefer a DX2 VLB build, and others go for a PCI DX4 or 5x86... it's your choice!

Count me in with team DX2 VLB. Just feels like the definitive 486 build as it was meant to be, where as DX4 or 5x86 builds feel more like "I couldn't afford a Pentium" builds.

dukeofurl wrote on 2024-07-05, 17:58:

That's very helpful.

In addition to socket 3 stuff, I'm seeing some boards that have 25mhz 5v 486 CPUs, stuff by micronics for instance. Is this socket 1? Do these have similar upgrade paths or not so much?

I'm not sure if that's socket 1 but yeah, you will find older boards and all kinds of aberrations =) Stuff was fun and less standardized back then.
You probably can get a DX2 to run on those boards. If the bus is limited to 25MHz, then your DX2 will run @50MHz. The Pentium OverDrive can theoretically run on those old systems too since it has a built-in VRM but I don't think it's that easy. Not all boards are compatible. And if you want to run newer CPUs you will face problems as most run at 3.3v so you could end up frying them =)

As for a 25MHz 486 I don't find it particularly significant. An Am386 DX40 is more interesting to me.

Namrok wrote on 2024-07-05, 18:06:

tauro wrote on 2024-07-05, 17:50:

Some people prefer a DX2 VLB build, and others go for a PCI DX4 or 5x86... it's your choice!

Count me in with team DX2 VLB. Just feels like the definitive 486 build as it was meant to be, where as DX4 or 5x86 builds feel more like "I couldn't afford a Pentium" builds.

Definitely... and it did quite well back then. But Quake was the 486 killer.

Just remembered something else.

If you can, get a board with a PS2 connector for the mouse. It's super convenient. Serial mice aren't as easy to find, and aren't as friendly, or as good as a modern optical PS2 mouse.

There are VLB boards with PS2 connectors. On the PCI boards you can even use a USB PCI card (preferably VIA for DOS support) and use a USB mouse.

tauro wrote on 2024-07-05, 19:22:

Serial mouses aren't as easy to find, and aren't as friendly, or as good as a modern optical PS2 mouse.

Really? I find serial mice are readily available on Ebay including NOS versions.

I've bought NOS Microsoft serial mice for my older systems and they work great.

There's also the option to use a PS/2 to 9 pin serial adapter.

Agree with PS2 mouse, it would be very convenient. Just wanted to add that 486 mobos are probably the richest with jumpers among most generations. Packs of jumpers for FSB, cache, processor, and god-knows-what 🙂

wbahnassi wrote on 2024-07-05, 19:46:

Just wanted to add that 486 mobos are probably the richest with jumpers among most generations. Packs of jumpers for FSB, cache, processor, and god-knows-what 🙂

On that note, needle-nosed pliers are a handy accessory for dealing with all those jumpers! 😀

Namrok wrote on 2024-07-05, 18:06:

Count me in with team DX2 VLB. Just feels like the definitive 486 build as it was meant to be, where as DX4 or 5x86 builds feel more like "I couldn't afford a Pentium" builds.

TBH, I find that even a DX2 build (i.e. DX2-66) feels like it should really be a Pentium. I ended up downgrading my own 486 build to a DX-33, since it's more ideal for speed sensitive games of the early 90s.

Though there is a nice range of performance options available for that class of processors. Lots of choices to tailor a build to ones' preference.

Shponglefan wrote on 2024-07-05, 19:41:

Really? I find serial mice are readily available on Ebay including NOS versions. […]
Show full quote

tauro wrote on 2024-07-05, 19:22:

Serial mouses aren't as easy to find, and aren't as friendly, or as good as a modern optical PS2 mouse.

Really? I find serial mice are readily available on Ebay including NOS versions.

I've bought NOS Microsoft serial mice for my older systems and they work great.

There's also the option to use a PS/2 to 9 pin serial adapter.

For the PS/2 to serial adapters, doesn't the mouse have to specifically support it? I tried a random adapter with a random PS/2 mice and came up empty before if memory serves, which it may not.

Namrok wrote on 2024-07-05, 20:36:

For the PS/2 to serial adapters, doesn't the mouse have to specifically support it? I tried a random adapter with a random PS/2 mice and came up empty before if memory serves, which it may not.

To be honest, I'm not sure.

I'm using an adapter that was included with one of my Microsoft PS/2 mice.

Namrok wrote on 2024-07-05, 20:36:

Shponglefan wrote on 2024-07-05, 19:41:

Really? I find serial mice are readily available on Ebay including NOS versions. […]
Show full quote

tauro wrote on 2024-07-05, 19:22:

Serial mouses aren't as easy to find, and aren't as friendly, or as good as a modern optical PS2 mouse.

Really? I find serial mice are readily available on Ebay including NOS versions.

I've bought NOS Microsoft serial mice for my older systems and they work great.

There's also the option to use a PS/2 to 9 pin serial adapter.

For the PS/2 to serial adapters, doesn't the mouse have to specifically support it? I tried a random adapter with a random PS/2 mice and came up empty before if memory serves, which it may not.

That is what I've read before. To further support the idea that difference serial mice act differently, I understand windows 3.1 automatically works with the Microsoft mouse, but the driver does not automatically work with my Logitech serial mouse.

For me personally I've got the world of mice covered. Have a Logitech serial mouse, a working adapter for ps/2 that I think came with it, as well as a few ps/2 mice.

There are basically two classes of 486 boards, original 5V models (pre 1994) and newer 3.3V stuff (post 1994). In my experience it’s hard to go wrong with a 5V board and classic intel 486. With the 3.3v boards the features can be less standardized and there are more jumper and BIOS issues.

Outside of OEM boards, they are rarely locked to a specific bus speed. Even the ones that are can usually be coaxed into other speeds by doing some minor board work.
Also be aware that many 5V boards set the bus speed with a crystal oscillator rather than a clock generator. On these boards you buy a new oscillator to change the bus speed.

My 486 experience was:
Socket 1 486dx-33 in 1992 ISA with OS/2 2.0, Mach32, pc speaker: civilization, lemmings, myst (got a cdrom and a sound card near the end)
Socket 3 486dx4-100 in 1994 VLB with Win95, s3 864, sb value 16: doom series, earthworm jim, warcraft, panzer general series

They were kind of similar but kind of different things. Both systems lasted 2 years like the one that came before (386sx/trident) and the one that came after (pentium/pci s3 virge) But the socket 1 system was constant effort to make things work while the socket 3 was the dawn of plug and play.

The only issues I had with my “socket 1” system were installing the modem, sound card and CD-ROM drive, but it was hardly the fault of the motherboard. Even if using jumperless cards you still need a basic understanding of resource management. Frankly I had more issues with PnP. There’s a reason it’s known as ”plug and pray”.
One other possible issue with older boards is the 512mb ide drive limit in the BIOS, but it’s hardly an issue now that you can use MRBIOS or XT IDE.

My first PC was a 486DX33 with a 340MB HDD and a Tseng ET4000 running DOS 5.0 I think. I upgraded it with a Sound Blaster 16 ASP and CD-ROM drive than came a set with some games and software.
Installing the SB16 card must have been the first time I opened a PC 😀.

Anonymous Coward wrote on 2024-07-06, 04:53:

The only issues I had with my “socket 1” system were installing the modem, sound card and CD-ROM drive, but it was hardly the fault of the motherboard. Even if using jumperless cards you still need a basic understanding of resource management. Frankly I had more issues with PnP. There’s a reason it’s known as ”plug and pray”.
One other possible issue with older boards is the 512mb ide drive limit in the BIOS, but it’s hardly an issue now that you can use MRBIOS or XT IDE.

The issues I had with the socket 1 build were mostly related to stuffing drivers into DOS upper memory blocks, fitting all my stuff into a 200MB hard drive (large at the time) and making things work with OS/2. It’s why I ended up with the Mach32 card. It had 8514a compatibility. I had spent time with the trident (slow) and a diamond speedstar 24x (driver hell) and that was most of the pain.

Builing a retro system, its easier to find mature drivers and people rarely mess around with as many tsr programs as I did at the time with dos ipx & tcpip stacks. But you do run into other problems more frequently like anachronisticallly large storage. Fortunately there are more and better tools to address that these days.

Plug&play wasn’t so much a problem for me. Maybe it was my home hardware, or maybe it was because I was working on a win95 early adopter rollout for 2000 end users, so I got pretty good at handling the outliers and quirks of the enumeration / arbitration / configuration stuff. But yeah, when plug&play didn’t go your way, it could be tough to get leverage on the situation to make the change you wanted.

I suggest taking some time to think about whether you want an ISA-only, a VLB, or a PCI 486 before going further.

dukeofurl wrote on 2024-07-05, 13:54:

Is it common for 486 motherboards to have jumpers for different fsb? For instance, I've seen some PCs that have 486sx25 CPUs and I'm wondering if those boards might be locked into a 25mhz fsb or if it would be very common to have jumpers or switches to change to something like 33mhz.

Older 486 boards are indeed locked at a specific speed because they use a discrete oscillator of the exact frequency wanted. In order to change the speed you'd have to take out that oscillator and put in a different one. Newer ones do use jumpers to change between bus speeds. Sometimes there are even undocumented speeds, such as the MB-8433UUD having 60 MHz.

dukeofurl wrote on 2024-07-05, 13:54:

Is the multiplier usually a setting adjustable on the board or is it embedded in the CPU? Like does a 486dx2 66 require a board that has a 2x multiplier setting on it, or not? Similarly I've heard of things like 486 100 and 133mhz processors. I think I've read that these CPUs interpret, eg, a 2x multiplier as a 4x multiplier, so you don't actually need to have a motherboard that utilizes a 3x or 4x setting via jumpers/switches to get the full speed of the cpu, is this right?

The DX2 CPUs are indeed, in today's terminology, multiplier-locked, with a multiplier of two.
Part of the reason for all the jumpers on a 486 board is that sockets had longer lifespans and more drastic changes than a CPU socket today, which tends to have a relatively short lifespan. Multiplier settings were retroactively added after 486 boards already existed and no 4x setting was provided. The other issue you had was Cyrix or AMD extending the socket to add some feature, and then Intel extending it in an incompatible way, and then Cyrix and AMD releasing their new CPU that switches to the Intel-standard pinout called P24D. The jumpers let you literally rewire the pinout of the socket to adapt it to your desired CPU and that's why it is so complex.