I had an IBM 300PL a few years ago. I believe it's pretty much the same computer as the GL, except with an AGP slot.

It was an OK machine. Had that nice IBM stability and was whisper quiet. I managed to get it upgraded to a Celeron 1400 with a Slocket and a Lin-Lin FCPGA-2 adapter.

However, I like my Dimension XPS T550 quite a bit more. It's just as stable and quiet, much easier to work with, and it uses standard AGP spacing (unlike the 300PL, which requires AGP cards with NLX-style mounting brackets). Plus, the Dell machine is a bit faster. Using the same Celeron-1400, 512MB of CL2 SDRAM, and a V3-3000 GPU, the Dell outperforms the 300PL across the board by 2-4%. These include benchmarks like 3DMark 99-2001, PCMark2002, SuperPi, Quake3, and demanding DOS games like Screamer 2 in SVGA.

This motherboard definitely uses BX chipset and should push beyond 100MHz FSB, but according to the sticker instructions, motherboard is a 66MHz FSB variant. Perhaps IBM, instead of designing a cheaper EX based motherboard, simply modified existing BX for entry level segment?

Write down PLL ICs model ("ICS", below DIMM slots), now it's the only performance limiting factor in that motherboard.

this is the ICS:

https://drive.google.com/file/d/1pAg2XRyGtbcu … ew?usp=drivesdk

i have made some test... i can’t manage it to go beyound 66mhz even with a regular 100mhz bus cpu:

i have tested:

PII 400Mhz (100x4) and in every combination of the selector goes to 266mhz (66x4 real)
PII 350Mhz (100x3,5) same above and always at 233Mhz
Celeron 366 (stock cpu) always at 366mhz

and the “strange” cpu: P2 300 SL2QC that accept every multiplier from 2x (133Mhz) to 5,5x (366Mhz). What a stange cpu... also that at 66Mhz Bus.

The last cpu is very interestin for retrogaming i think because it can go from a very slow “like P133MMX” to a P2 366Mhz.

It's simple : that CPU is unlocked

yes yes, i come from a long overclock story starting from Pentium1.... but only the first klamath are unlocked, and is not so easy to have a completely unlocked cpu... and about the 66/100mhz bus?

Not really, from what I've read and experienced, most if not all Klamath are unlocked. First Deschutes are too, then they started to semi-lock them (no more higher than needed multiplier available) and finally they fully locked them. Celerons are all locked.

Here's PLLs datasheet, pin 16 selects between 66 and 100MHz FSB (see pg. 2).

Pin 16 pulled to ground (L) - 66MHz, pulled up (H) - 100MHz.

Remove motherboard from case and try to trace where it goes, it can be permanently connected to ground, if not, it could go to slot1 "BSEL" pin, in that case CPU FSB is selected automatically by CPU. This PLL has i2c bus and can programically set FSB up to 133MHz (see pg. 4, "Byte3" table).

*I hope you are reading those CPU frequencies from programs like CPU-Z, rather what is displayed on screed during POST or in BIOS (which can dispay false CPU freqs).

Yes i have check the frequency with cpu-z.

Before remove mainboard and doing deeper modifyed let me say WHAT I CAN ASK at this computer.... please reply at my point if necessary.

1)His target is DOS retrogaming, from 1991/92 to 1999 approx. NO early dos game like CGE, EGA ecc... for this i can take a 286...

2)I have also a P4 3.0ghz which can continue where the IBM 300GL has no power to play games.

3) This IBM 300GL have no AGP and i can't use a easy to find graphic card, but as i already say, for more complex game i can use a Pentium4

4)My Pentium 4 not have ISA, not sounblaster PRO or 16 that i have in my 300GL, but i think is not a problem because in very late '90 years is not important a sounblaster OPL... correct?

5)i have a SBC that i use in my A4000 wich work very well, it has a P233MMX that can go from 120Mhz to 250Mhz with the possibilities (is a supersocket7) to use a K6-3 (450mhz already have), the problem with this SBC is that for using it i must keep ON a 3500€ amiga4000.. is not really clever or not? From that i start to search a complete pc and i found this IBM 300GL. this 300GL must doing a work made by this SBC (i have seen that i have a P2 300 that go from 133mhz to 366mhz and i think that is ok for replacing a SBC 233mmx, correct).

Thanks for your reply....

AlessandroB wrote:

Before remove mainboard and doing deeper modifyed let me say WHAT I CAN ASK at this computer.... please reply at my point if necessary.

I don't quite understand what you mean.

At this point you basically have a i440FX system - no AGP and only 66MHz FSB, but with SDRAM. If you could make it run @ 100MHz FSB, you could also install any PIII katmai or coppermine CPU (for that, uCode update might be necessary), add any PCI DX6+ 3D video card and game late 90's games without a hitch. You already have a PPGA slotket, mod it and install a 1GHz FC-PGA PIII into your IBM 😀

Hope that helps to decide.

those points are my considerations on the retro game and what I would like this computer to do. I would like to know if the goals I have set can be achieved, for example if there is a too big power gap and I have a hole in which the IBM I have is too slow and the Pentium4 unfit to cover that gap.

if i can't go to 100mhz bus, Whit a PentiumII 300 (max cpu at 66mhz bus) and a PCI video card (wich one?) i can play games until 1999?

Yes, that IBM PC would meet your requirements, except maybe for gaming late 90's games like UT99, Q3, NFS high stakes etc, games would run with PII 300, but CPU would create a bottleneck, regardless which video card you'd be using. Gaming experience with such CPU wouldn't be pleasant. In your place I'd try to do the following: make MB run @ 100MHz FSB, install a 600MHz+ PIII, get a DX7+ compatible video card, like GF2/4MX PCI, FX5200, radeon 9200 etc. With such setup you could play games from early 2000's easily.

I do not think this maninboard can reach 100mhz without deeper modification... and i not want to loose the integrity of this 300GL if is not really really necessary. Probably i can install a 600mhz but at 66*6=400mhz. we well see... About the graphic card, wich is the order from best to worst? 1)FX5200 2)4MX ecc...

Like I mentioned, take a look at "Softfsb", this software directly talks to the PLL and thus might let you set 100MHz fsb !
This is kinda neat because it lets you change the CPU's speed on the fly, so if a game is just a little too fast, slowing down the CPU will help

softfsb make the system crash i select not the mainboard but the "Target Closk generator" -> ICS 9148xx-60. Is correct?

exhist a 370 to slot1 that force mainboard like mine to work at 100mhz bus???

You have to figure out the schematic of pin 16 of "ICS" PLL. It's probably permanently tied to ground and no CPU would bring that pin up to the Vcc of 3.3V (H). Maybe there is a simple 0 Ohm resistor or jumper that connects pin 16 to ground, in that case, all you'd need to do would be removing it and connecting 10k Ohm resistor from 3.3V to that pin.

You're probably right, and I'm amazed at your great competence, the whole forum is great. I do not think of making this change because I do not want to change the historical originality of the computer and above all I am not necessarily looking for the maximum performance but for those NECESSARY for the games at beginning, middle and (for what this computer can) end of the 90s. To this point I wonder: with the fixed bus at 66mhz the two cpus with the highest multiplier NON COPPERMINE are the Celeron Mendocino 533mhz and the pentiumIII600mhz (which would work at 400Mhz). Which of the two is better performing? I think the mendocino because the greater cache of the pentiumIII does not make up for the 133Mhz of difference in favour of mendocino...

AlessandroB wrote:

I do not think of making this change because I do not want to change the historical originality of the computer

I understand, I also do not like to mod old hardware, but if it's a soft-mod, which can be reverted back to the original state anytime, then I don't mind those. It's the hard-mods, like cutting traces, drilling vias, etc., that I completely despise.

Looking at the PCB near pin 16, you can notice that a resistor marked "R149" is missing, maybe all you'd need to do to enable automatic FSB detection would be installing it. The mod should not be too hard, knowing that exact same motherboard PCB was used for 100MHz motherboard variant.

AlessandroB wrote:

Which of the two is better performing?

Yes, 533MHz mendocino would outperform 400MHz PIII.

the only thing I have to do is weld a 10kohm smd resistor in that place?

It might be just one of the steps. Measure for continuity between pin 20 (3.3V Vcc) and via that would connect to R149, if multimeter shows that it is a common node, then R149 is a pull up resistor. Measure for continuity between pin 19 (or any ground point) and pin 16, repeat measurements with and without CPU (try PII with 66MHz and 100MHz FSB), see what happens. I think that pin 16 might still go to "BSEL" pin of slot 1, if both 66/100MHz FSB CPUs do not change the readings, then it's permanenty connected to ground (I presume).