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486 Overdrive, questions.

Yes, on the 486SX 25 the multiplier is x1 so internal speed and external bus speed are the same: 25 MHz

orion24 said:
Yeah, if there is a jumper to change the BUS speed from 25 to 33 MHz, you do that, even if you don't change the CPU. Almost every 486SX-25 can work fine at 33 MHz. My 486SX-25 board from IBM has no jumper to set the clock and the only option is to change the 50MHz oscillator to an 66MHz one.
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That's true. I have done it with a soldered 486SX 25 without heatsink and without fan.

If you want to retain the "mistique" of 486 you can use an Intel Overdrive, which is a special 486DX2 or DX4 with heatsink included. The fastest model is: http://xhoba.x86-guide.com/en/collection/Intel-Overdrive-486DX4-100-(PGA168)-cpu-no5377.html
But again, to get the maximum 100 MHz you'll need to set external bus speed at 33 (its multiplier is x3).

About the eBay article, yes, the PODP5Vxx are the Pentium Overdrives for socket 2 & 3 486 boards, with xx being the speed. The BOXPODP5Vxx are the ones sold in beautiful box :) Probably an unboxed one will be cheaper, provided that you are not a box collector.

Take a look at these 2 different blue sockets:
http://www.computerhope.com/jargon/o/overdriv.htm
http://en.wikipedia.org/wiki/Socket_2

You don't need to count the pins, but notice that the 1st one has 3 rows of pins, while the 2nd one has 4. The Pentium Overdrive was officially designed for the 2nd one.
 
A picture of the PODP5V83 top and bottom side:
http://pccpu.wordpress.com/2009/12/10/intel-pentium-overdrive-83-podp5v83/

You can see it has 4 rows of pins, that's why officially it requires a socket 2 or 3. According to the thread I told you yesterday it can also be plugged on the 168/169 sockets and it works with the remaining pins on air... But I have never tested it. Also, I'm not sure that all the remaining pins will be on air, maybe they hit some part of the socket when you try to plug it. As I said, I have never tested it.
 
Rauli: Pentium Overdrive 83Mhz is the only kind available on Ebay right now (not the 63Mhz), and 486 Overdrive are as expensive and used. Though on a website, they say the Pentium Overdrive is like a 486, just the name changed. It's ok if it run at 63Mhz instead of 83Mhz because of the bus speed, because i have Socket7 boards here and many real P1 CPUs, 100Mhz up to 200Mhz.

But yeah...thinking about it, the Pentium Overdrive have a fan, while the 486 doesn't. I would need to know if regular Socket1 CPUs (not Overdrive) work on a Socket2.
 
RaptorZX3 said:
I would need to know if regular Socket1 CPUs (not Overdrive) work on a Socket2.
Click to expand...

AFAIK:
  • Socket 1 with 168 pins supports 5V regular CPUs and some (168-pin) Intel* Overdrives.
  • Socket 1 with 169 pins supports 5V regular CPUs and all Intel* Overdrives.
  • Socket 2 support 5V regular CPUs, all Intel* Overdrives and some AMD and Cyrix "enhanced" 486 models.
  • Socket 3 support 5V regular CPUs, all Intel* Overdrives, Pentium Overdrives and some AMD and Cyrix "enhanced" 486 models.
  • Socket 3 should support also all 3.3V 486 compatible CPUs (including all AMD and Cyrix "enhanced" 486 models) but some boards lack the 3.3V regulator and then the socket doesn't support them.

(*) With "Intel Overdrive" I don't mean any Overdrive made by Intel, but a "486 Overdrive" which Intel named "Intel Overdrive".

So, socket 2 supports regular 486s. The problem is that your board has another 486 which you don't know how to disable, or if it is possible to disable. And having 2 enabled 486s in the same board will likely kill it.

That's all I know about Intel Overdrives, Pentium Overdrives, socket 1, 2 and 3. And I still don't know which type of socket you have.
 
So this is why i'll look for an "ODP" model which have the extra pin to supposedly disable the embedded CPU, like the "DX2ODP66". Funny i found someone selling them, but he typed in "DX20DP66" (the 0 which is the number zero), it's been pulled from working Compaq computers, but with time he's unsure if it work or not (?) but the pins are straight. He got 2 of them...
 
Yes, on my experience I can say it will likely work. But be aware that it is a 2x processor, so with a 25 MHz external bus it will run at 50 MHz. If going from 25 MHz without FPU to 50 MHz with FPU is enough for you, go for it!
 
Rauli said:
Socket 3 should support also all 3.3V 486 compatible CPUs (including all AMD and Cyrix "enhanced" 486 models) but some boards lack the 3.3V regulator and then the socket doesn't support them
Click to expand...

Yeah, those voltage regulators. I hate them and you can see problems the other way around as well, as some (for not to say most) late socket 3 boards do not support 5V CPUs and those that support might need an optional voltage regulator. I had that curiosity at the back of my head, as to why weren't they using the directly available +3.3V and +5V lines from the PSU and they wanted a regulator. Probably just cheaper to design, or maybe they didn't want the simple switch of a jumper to kill a 3.3V CPU from an incautious builder or end-user.
 
orion24 said:
I had that curiosity at the back of my head, as to why weren't they using the directly available +3.3V and +5V lines from the PSU and they wanted a regulator.
Click to expand...

I suppose (but this is just a supposition) that CPU voltages have to be more constant that the PSU can supply. So, an extra regulator is always needed. And the input of a regulator must be higher than the output (let's say 2V higher). So that both the 5V and 3.3V lines for the CPU must be taken from the 12V PSU line and 2 different regulators. I repeat that this is just a supposition, I would like to hear what an expert in electronics has to say.
 
there ARE jumpers around the embedded CPU, and i just checked inside the cover and there's a picture and what the jumpers do.
board_jumpers_settings.jpg
Though it only show up to 40Mhz, and i must say it's confusing me with different settings doing the same thing...But if i put a DX2ODP66 on that, can i make it run at 66Mhz? Or maybe the CPU speed selection is only for the embedded CPU and once i install the Overdrive on it, it'll just run at the new CPU speed?

Sorry about the flash, but it does show what i need to show here.
 
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Oh, everything would have been very easy with that photo.

To change clock you must change J23, J25 and J26 to their, let's say, 33 MHz position. Please, confirm that they are now in the 25 MHz position.

And with J34 and J40 (or whatever number they are, I can't see them very good) you can select the type of CPU that you are going to use on the socket 2 (at least, the picture depicts a socket 2). So you can use a regular 486DX. It's documented, so you don't need an overdrive. In fact, the sheet doesn't mention overdrives (though they should work as well). Please, confirm that they are now in the "None IN" position. When you plug a 486DX, DX2 or overdrive configure them in their 486 DX IN position. I bet that the soldered 486SX is only enabled in the "None IN" position.

So, get a 486DX2 66MHz, which will be cheap, plug it on the socket, configure your board for 33 MHz CPU clock and 486 DX IN, and voila.

Don't mess with the 40 MHz position, it's just for DX 40 (not for DX2 40) and for AMD 486DX2 80. If you get the later, make sure that it not a 3.3V CPU.
 
hmm ok, but would an Overdrive be better since it have an official heatsink attached on it? There is no bracket to hold a heatsink on a Socket1/Socket2, and i don't have thermal glue here.
 
You should get a heatsink especially if you get a 5v clock doubled chip. My Intel 486-66 had a heatsink built into the ceramic shell. I don't know if you can find them anymore but there used to be clip on heatsinks for a 486 which would work well. If you can mount a fan on the heatsink, so much the better. That is one cramped case. Anything you can do to encourage airflow will help prevent overheating.

You don't have to get an Overdrive branded chip but if you find one for close to same price as a 486 then take it. Make everything simpler.
 
yes, i found one DX2ODP66 with the Overdrive heatsink on it, so...yeah, and it's about the same price too (18-19$US + about 8-9$US for shipping to me maybe), untested, but many told me it's reliable enough and the seller told me it's been taken care of even after all these years.

edit: i bought that from that seller i talked about:
http://www.ebay.com/itm/321451172943

it's maybe as expensive as the regular 486, so...might as well take the 169-pins 486 Overdrive made to fit AND this extra pin also act as the KEY so it won't be inserted in a wrong way!
 
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The 66 MHz overdrive is like an original DX2 66 plus heatsink, and more modern, so it will probably have a better L1 cache performance and save some energy. In addition it will have some features not present in the original 486, like the CPUID instruction, which will not increase performance at all, but is nice to have. Also, the Intel Overdrive has a better look :)
 
i got it today, and did the jumpers settings for the processor. Now with the 33Mhz setting...does it mean it'll run at 33Mhz, or 66Mhz? Will the processor double its speed by itself since it's DX2?

Well all in all, for this computer, now i need a good VGA ISA card (SVGA VESA compatible with 1mb) and eventually an IDE to CF adapter.
 
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The processor should be running at 66MHz by default. Clock doubling is automatic except that some systems could turn it off with BIOS settings or motherboard jumpers for troubleshooting.
 
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