Most uncommon 486 chips

[Unknown_K]

While looking over a box of CPU's at the local recycler I found a Cyrix 486 DX2 80? and a 486 DX4 100 that I snagged (seems like most 486's are AMD and Intel). So I started thinking about what the most uncommon 486 CPUs to collect are (what to look for). I also found a TI? 486DLC that fits in a 386 socket (normal pin type).

 

[Raven]

Ti branded, ST branded, UMC branded, Intel Pentium Overdrives (if you count them), Intel Overdrives (particularly the older non-100mhz versions), any 486 chip that isn't 25mhz, 33mhz, or 66mhz by Intel (at least in my experience), IBM branded chips, Am5x86 chips at 150 or 160mhz, Am486 chips at anything but 66 or 100mhz, and Cyrix chips at anything but 100mhz.

The holy grail of 486s is the 150mhz or 160mhz Am5x86 as far as rarity goes - it's widely believed that they never even reached mass production.

All of the above is based on my experience.

486-man to the rescue?

 

[k2x4b524[]

How about a 486-DX-50?

 

[Raven]

Yeah, as I said, anything by Intel that wasn't 25, 33, or 66.

 

[Anonymous Freak]

Yeah, I remember having a raging debate with a friend over which was better, his 486DX-50 or my 486DX2-66. (We also had sound card arguments, his Gravis Ultrasound vs. my Sound Blaster 16, and later AWE32.)

Later in life, we got into Mac vs. PC arguments, Linux vs. Windows, and most recently, iPad vs. Netbook. I think we're doomed to argue the merits of one computing technology over another forever.

Thankfully, we agree on vi vs. emacs.

 

[Unknown_K]

How about a 486-DX-50?

Few companies used the DX/50 (50FSB was not very common and played hell with VLB cards), the DX/2 50 was more common.

 

[Dave Farquhar]

Yeah, I remember having a raging debate with a friend over which was better, his 486DX-50 or my 486DX2-66. (We also had sound card arguments, his Gravis Ultrasound vs. my Sound Blaster 16, and later AWE32.)

I can see the argument that a DX/50 would outrun a DX2/66 for anything that was memory intensive. But since VLB topped out at 40 MHz (and sometimes was questionable even at that speed), what do you do? Run the local bus at 25 MHz? (Not sure what the DX/50 boards did). Use ISA for everything?

It was certainly a lot easier to build a fast, reliable, soild DX2/66 than a DX/50. For most people it was worth the trade-off.

I know IBM experimented with running Intel DX4s at 2x50 MHz, but I don't know if they ever released anything in that configuration. It would have been wicked fast, but it sure pushed the limits of the day.

 

[Raven]

They ran VLB at 50mhz and it was considerably less stable. If you could find a video card that worked at that speed reliably, you'd have a brilliant system. Otherwise you'd have issues, and I've heard that the more cards you put on the bus the worse things get. I.e., if you just use a video card you might be OK, but if you rely on VLB for several things you should definitely not be running at that FSB.

You always have the alternative of finding a PCI board or just sticking with ISA and ignoring the presence of any VLB slots you may or may not have.

 

[Dave Farquhar]

That explains a lot. Once you'd used a 486 with local bus video, you couldn't stand one without it. And once you used one with local bus IDE, you couldn't stand to live without that either. So you pretty much wanted both of those on the local bus. I remember at least some VLB boards having a third slot, but I don't know what you would have put in there, except maybe another IDE card.

Of course today, since you wouldn't be using one of those as your primary system, sticking with ISA is a more tolerable option than it would have been in 1991 or 92. I can't imagine what it would have been like to plunk down three or four large for a system, then have to cripple that blistering CPU by putting the video and disk subsystems on an 8 MHz bus from 1984.

 

[Fake Al Gore]

In that case, wouldn't a 50 MHz 486 have been perfect for small-scale scientific research at the time? I'm sure specialized RISC-based machines would have been better than that, but you couldn't beat the price of the 486. If I remember correctly, most of the 50 MHz machines I saw advertised in computing magazines at the time were paired with larger amounts of RAM than the average user would have required (8 MB and more).

 

[Chuck(G)]

That explains a lot. Once you'd used a 486 with local bus video, you couldn't stand one without it. And once you used one with local bus IDE, you couldn't stand to live without that either. So you pretty much wanted both of those on the local bus. I remember at least some VLB boards having a third slot, but I don't know what you would have put in there, except maybe another IDE card..

I've got a 486 box somewhere here with an Adaptec 2840 SCSI adapter.

 

[Unknown_K]

There are also VLB network cards (I have 2 different models of those), and SCSI caching controllers (a lot of fun). The EIDE caching controllers with 16MB of RAM and a 286 chip on board are fun to use as well.

Most other cards didn't need the VLB bandwidth so ISA was fine for those. Everything on the VLB bus stole cycles from the CPU getting to its cache, add a few wait states when trying to use a 50Mhz VLB and you slow down the CPU even more.

I could be wrong but most DX50 systems were probably EISA workstations or servers, and the VLB variety were probably as well. The best 486 gaming rigs are 33/40 FSB, the worst are the 25's.

 

[Anonymous Coward]

I didn't have good luck with 486 chips on the 50MHz bus. The problem I've found is that you can't get good enough SRAM cache memory to make 50MHz worth while. In all setups I've had, it was necessary to add one or two extra wait states to keep the system stable. A well tuned DX/2-66 should be able to match the memory bandwidth of a 50MHz system with a few wait states, plus you have better integer performance, and a stable VL bus. A well tuned system with 40MHz bus will eat 50MHz bus memory scores for breakfast. The only advantage I have found with 50MHz bus is when you have VLB cards that work reliably at that speed. 50MHz VLB video is indeed very fast!

 

[IBMMuseum]

I didn't have good luck with 486 chips on the 50MHz bus. The problem I've found is that you can't get good enough SRAM cache memory to make 50MHz worth while. In all setups I've had, it was necessary to add one or two extra wait states to keep the system stable. A well tuned DX/2-66 should be able to match the memory bandwidth of a 50MHz system with a few wait states, plus you have better integer performance, and a stable VL bus. A well tuned system with 40MHz bus will eat 50MHz bus memory scores for breakfast. The only advantage I have found with 50MHz bus is when you have VLB cards that work reliably at that speed. 50MHz VLB video is indeed very fast!

There were two 486DX-50 complexes for the microchannel PS/2 Model 90 and 95s. The "Type 1" complexes were built in versions for the CPU base clocks of 20, 25, 33, and 50MHz. An 256Kb L2 cache daughtercard was an option for the Type 2 complex, on the 486DX-50 version it was with 15nS cache chips (others were 17nS).

The "Type 3" was only made in a 486DX-50 version (in IBM sub-model coding, the middle of the three digits denotes the CPU and speed, in this case an 'M' for a 486DX-50), with integrated 256Kb L2 cache chips on the double-decker complex. I can't remember if the chips were rated at 12nS or 15nS off the top of my head. For the 50MHz T1s, I think it had a wait-state that was automatically set for the L2 cache.

 

[IBMMuseum]

Ti branded, ST branded, UMC branded, Intel Pentium Overdrives (if you count them), Intel Overdrives (particularly the older non-100mhz versions), any 486 chip that isn't 25mhz, 33mhz, or 66mhz by Intel (at least in my experience), IBM branded chips, Am5x86 chips at 150 or 160mhz, Am486 chips at anything but 66 or 100mhz, and Cyrix chips at anything but 100mhz.

The holy grail of 486s is the 150mhz or 160mhz Am5x86 as far as rarity goes - it's widely believed that they never even reached mass production.

All of the above is based on my experience.

486-man to the rescue?

Yes, the more rare are other brands than Intel or AMD. For Intel, initial speeds (12 or 16MHz) and steppings (A0 and A1) are quite rare. I have also never seen an Intel 486DX2-50 or 486DX2-66 in "Overdrive" packaging that had the 143xh CPUID like it should have (and there seems to only be one S-spec of each speed for the 486DX4-75 and 486DX4-100 identifying themselves that way).

Here is the CPUID/S-spec work I did for Intel 486 CPUs: http://www.IBMMuseum.com/Intel486.htm

 

[vwestlife]

How about this for an oddball 486? 30 MHz x 3. I've never even heard of a motherboard which supports 30 MHz bus speed.

Intel created this weakling in response to OEMs who wanted the cheapest possible "Intel Inside" 486 to sell (a stunt they would later pull again with the Pentium-75).

There are all sorts of oddball 386SX and 386DX-based "486" chips from Cyrix, IBM, TI, SGS-Thomson, etc.: 486SLC3, 486BLX3, 486SXL2, 486DRu2, 486SRx2, 486SLC/e-V, etc....

 

[sombunall]

I actually have stories. I once upgraded a 486dx-33 to a 486dx-50. I could not get it to work with the L2 cache on. The SIS motherboard had removable cache and tag cache. I think the tag cache was 20ns and the cache was 25ns. For some reason I decided it was the tag cache so I went out trying to find them and failed. I ended up running it without L2 cache and back then I didn't know what wait states did, nor did the guy who installed it. It was still faster even without L2 cache on but I always wondered how much faster Hexen would have run.

I also have another embarrassing story. I bought a pentium VX motherboard and then waited half a year before buying the CPU and memory (don't ask). I bought the CPU at a different store and it was an AMD 5x86-133 that I thought was a pentium. The jerks at the store didn't tell me it wasn't. Well I tried to fit that 5x86 into a pentium ZIF socket for half an hour before my dad finally came in the room and realized they were not pin compatible. I ended up buying the right 486 motherboard for the 5x86 and using it for 6 months before going for the pentium. I ended up using the 5x86 as a dial up modem proxy server.

I still have the CPUs but the 5x86 motherboard got fried by a lightning strike. The CPU is fine but now it is in a motherboard that can only use it as a 33x3 CPU or a DX4-100 (should have been called DX3-100 right?). Now I surge protect everything with power bars rated with at least 1700 joules.

 

[Chuck(G)]

I've seen AM486DX5-133 chips. They've got to be uncommon.

 

[Raven]

I've seen AM486DX5-133 chips. They've got to be uncommon.

An Am486 and an Am5x86 are the same chip - the Am5x86 is just a marketing name to place them in the league of the Pentium (at least in the mind of the consumers). The Am486DX5-133 is just a very early revision Am5x86-133 prior to that change. It's the same chip really, but the labeling makes it rare. Personally I'm not interested in how a CPU is labeled, it's all about the underlying hardware for me.

Due to that, I didn't mention a few other rare chips with different colored text, etc. I also didn't bother to memorize them as I did the details of most 486 chips.

 

[Chuck(G)]

An Am486 and an Am5x86 are the same chip - the Am5x86 is just a marketing name to place them in the league of the Pentium (at least in the mind of the consumers). The Am486DX5-133 is just a very early revision Am5x86-133 prior to that change. It's the same chip really, but the labeling makes it rare. Personally I'm not interested in how a CPU is labeled, it's all about the underlying hardware for me.

I knew that, but this thread seemed to be concerned with chip labeling. When you get down to it, there aren't that many different (internal) 486 chip varieties.