SECC and SECC2 refer to the way how the cpu's are packaged. It has nothing to do with the functionality and only with how they are fitted on the motherboard. If you have a motherboard with brackets that cause problems or limit your possibilities you can easily replace them with universal brackets. see illustration below

I think there are SECC Pentium III CPUs but only engineering samples. You can find pictures of them on CPU World for example.

PARKE wrote on 2025-03-07, 10:39:

SECC and SECC2 refer to the way how the cpu's are packaged. It has nothing to do with the functionality and only with how they are fitted on the motherboard. If you have a motherboard with brackets that cause problems or limit your possibilities you can easily replace them with universal brackets. see illustration below

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Thanks for that - I didn't realise it was purely a mounting mechanism change. Assuming I'm interpreting this correctly, so long as I was willing to dive into DIY solutions, I could theoretically put a much later and higher clocked Slot 1 P3 in it, assuming I had enough space for it and a cooler.

Paar wrote on 2025-03-07, 10:49:

I think there are SECC Pentium III CPUs but only engineering samples. You can find pictures of them on CPU World for example.

The ebay auction I was looking at has a bunch of them listed, with these images:

https://i.ebayimg.com/images/g/X7UAAOSw~YlnUyYz/s-l1600.webp
https://i.ebayimg.com/images/g/tSAAAOSwn8tnUyZD/s-l1600.webp

Which sort of looks SECC-1-ish to my eye, but as this thread establishes, I am certainly not an expert on that! The P3 450mhz seems to be the only one on SECC-1 but I suspect it may simply be rare, rather than engineering-sample-rare.

Welcome to this fun but sometimes confusing hobby 😀

Good news: as PARKE says, SECC1 vs 2 package is the least of your worries.

In fact the Slot 1 platform is probably second only to Socket 7 in terms of longevity and complexity of CPU support. There are no less than five relevant factors:
- CPU package (SECC1 or 2, or SEPP in some cases) - purely a question of brackets. In fact unless you have a very heavy cooler, you can get away with removing the brackets entirely.

But then there's:

- CPU voltage support: 2.8V, 1.8V, 1.6V or 1.45V needed depending on CPU core type
- BIOS support for the CPU core (6 different CPU families, sometimes with multiple relevant steppings)

If those two aren't in order, your system won't even be able to boot. There are two more that will determine if it can run at correct speed:

- FSB (bus speed) support: 66, 100 and/or 133MHz
- Multiplier support: only relevant for early unlocked CPUs or later engineering samples. Later CPUs have fixed multiplier and ignore whatever the motherboards tell them anyway.

What does that mean for your situation, having a Dell Opltplex with P2-233MHz CPU and wanting to run a Slot 1 Pentium 3?

Firstly, we'd need to know exactly which motherboard is in that Opltiplex to be sure, but the indications aren't good:

- P2 233 is the first and oldest Slot1 CPU, running at 3.5x 66MHz and with its old Klamath core, requiring 2.8V power.
- if that CPU is original for the system, it's hightly likely it has an i440LX chipset which dupports max 66MHz.
- Dell is an OEM and OEMs in general tend tp ship systems with limited BIOS which will frequently refuse to run unsupported CPUs.

It's very likely you'll be limited to 66MHz FSB, which rules out P3 CPUs which start at 100MHz FSB. Moreover it's very likely that the board can only offer power over 1.8V and possibly only 2.8V. In the latter case, you are limited to the three Klamath P2 CPUs (233, 266 and 300MHz). If it goes down to 1.8V, you might be able to use Deschutes P2 CPUs (333MHz) or Covington or Mendocino Celeron CPUs. If the latter works, a Celeron 433 would be the fastest CPU you could run without an adapter and with a 'slocket' adapter from So370 to Slot 1, you could go up to Celeron 533 (just be sure to get the black-and-steel PPGA version, not the green and ceramic FC-PGA). But again, it's possible you may be stuck with max P2-300.

To be sure, find out exactly which motherboard is in your Optiplex systems - or failing that, exact model numbers of the systems themselves. I fear it might be this one.

dionb wrote on 2025-03-07, 11:14:

Welcome to this fun but sometimes confusing hobby 😀

Good news: as PARKE says, SECC1 vs 2 package is the least of your worries.

OptiPlex GXa is right - although it's not in front of me at the moment. From all of this information, I am certainly glad I asked before buying anything else. I'll double check my parts properly once I get drives installed in them, but it seems like the juice is probably not worth the squeeze here.

ThoseDeafMutes wrote on 2025-03-07, 11:06:

https://i.ebayimg.com/images/g/X7UAAOSw~YlnUyYz/s-l1600.webp
https://i.ebayimg.com/images/g/tSAAAOSwn8tnUyZD/s-l1600.webp
Which sort of looks SECC-1-ish to my eye, but as this thread establishes, I am certainly not an expert on that! The P3 450mhz seems to be the only one on SECC-1 but I suspect it may simply be rare, rather than engineering-sample-rare.

That is a SECC2 package but the heatsink that fits in the motherboard brackets is missing.

ThoseDeafMutes wrote on 2025-03-07, 11:24:

dionb wrote on 2025-03-07, 11:14:

Welcome to this fun but sometimes confusing hobby 😀

Good news: as PARKE says, SECC1 vs 2 package is the least of your worries.

OptiPlex GXa is right - although it's not in front of me at the moment. From all of this information, I am certainly glad I asked before buying anything else. I'll double check my parts properly once I get drives installed in them, but it seems like the juice is probably not worth the squeeze here.

If that's it, take a look here:
https://www.angelfire.com/wy/DellOPTIPLEX/Gxa.htm

It appears that it supports voltages down to 1.8V and with BIOS version A09 it will support Celeron Mendocino CPUs, so you can use up to Celeron 433 natively on Slot 1, or get yourself a slocket (for Mendocino, any one will do) and get a Celeron 533 for max upgrade.

The site mentions using a Powerleap PL-iP3 adapter to get Coppermine Celerons up to 766MHz to work. That is impressive - but those adapters are complete unobtainium and if one turns up it tends to sell for ten times more than these systems are worth. The second option of an adapter with voltage jumpers set to 1.8V should also work, but comes with complexities I'd not recommend for your first retro foray. Stick to Mendocino, a Celeron 533 will perform pretty much on par with a P3-450 which is what you wanted anyway.