Deskpro processor upgrade


This article contains ancient wisdom that took many hours to piece together from old internet posts and datasheets...

There are three generations of Pentium 3 processors: Katmai, Coppermine (and Coppermine-T) and Tualatin. There are also Coppermine and Tualatin-derived Celeron processors. There are four packages: SECC2 for Slot 1; PPGA, FC-PGA and FC-PGA2 for Socket 370. FC-PGA2 chips have an integrated heat spreader. Furthermore, Mendocino Celeron (PGA), Coppermine (FC-PGA / FC-PGA2) and Tualatin (FC-PGA2) use different Socket 370 variants that are backwards but not forwards compatible, e.g. a Tualatin won't work in a Coppermine socket without an adapter.

I had read anecdotal evidence that my Compaq Deskpro EN SFF could support CPU upgrades including the highest-generation Pentium 3 (and Celeron derivative) processors - the Tualatin. However, I decided to take it step by step and do some research and a cheaper upgrade first. After some hours of research, I was able to construct the following tables. Note that some info still isn't clear to me:

Pentium 3 processor generations. 370(C) and 370(T) refer to Coppermine and Tualatin socket 370 pinouts.
SocketMax clock (MHz)FSB (MHz)Cache (KB)Voltage (V)
KatmaiSlot 1600100 / 133512~2.0
CoppermineSlot 1 / 370(C)1100 / 1130100 / 133256~1.7

There's also a Coppermine-T variant which can use Tualatin bus voltages. I'm not clear on what the purpose of these is but they should with both Coppermine and Tualatin boards.

Celeron processor generations. 370(M), 370(C) and 370(T) refer to Mendocino, Coppermine and Tualatin socket 370 pinouts.
SocketMax clock (MHz)FSB (MHz)Cache (KB)Voltage (V)
MendocinoSlot 1 / 370(M)53366128~2.0
Coppermine370(C)110066 / 100128~1.7
VRM specs
8.22.05 - 1.8Katmai / Mendocino
8.32.8 - 1.8Xeon
8.42.05 - 1.3Coppermine
8.51.825 - 1.05 (.025v increments)Tualatin

Conclusion: VRM8.4 (Coppermine) is fine for Tualatin, some chips (1.475V) will run slightly lower (or higher, if so configured) voltage. However, it's best to check your VRM's datasheet.

Additionally, newer processors might use a lower voltage, but have a similar TDP as older processors. This means the current (and heat) through the CPU power supply components and traces increases. More specificaly, MOSFETs must be able to deliver that much current and be able to deal with the heat, perhaps with the addition of a heatsink.

VRM 8.2 specs
VRM 8.3 specs
VRM 8.4 specs
VRM 8.5 specs

Voltages in these tables are approximate. Each CPU family uses a range of voltages; the exact voltage depends on the specific CPU model. 370(M), 370(C) and 370(T) refer to Mendocino, Coppermine and Tualatin socket 370 pinouts.

Upgrade options for Slot 1 motherboards - Everything with higher voltage and/or lower FSB can also be used.
Max. FSB (MHz)**
Min. VRM voltage*CPUAdapterCPUAdapterCPUAdapter****
~2.0Katmai (133)Katmai (100)
Coppermine (100)
Tualatin Celeron

370(C) w. VRM
370(T) w. VRM
Pentium 2 (Deschutes)
Covington Celeron
Mendocino Celeron
Mendocino Celeron

~1.7Coppermine (133)
Coppermine (133)

Coppermine (100)
Coppermine Celeron (100)
Tualatin Celeron
370(T) w. VRM#
Coppermine Celeron (66)370(C)
~1.5Tualatin370(T)#Tualatin Celeron370(T)#
Upgrade options for Socket 370 (Coppermine) motherboards - Everything with higher voltage and/or lower FSB can also be used. 370(T) refers to Tualatin socket 370 pinout
Max. FSB (MHz)**
Min. VRM voltage*CPUAdapterCPUAdapter
~1.7Coppermine (133)Coppermine (100)
Coppermine Celeron (100)
~1.5Tualatin379(T)##Tualatin Celeron370(T)##

* Check VRM spec/datasheet, BIOS, jumpers.
** Lower FSB is always supported. Higher FSB chips will run at max. motherboard FSB.
*** AGP bus overclocked on 440BX
**** A 370(C) adapter will work in place of a 370(M) adapter. 370(T) will work in place of 370(C). But I'm not sure if 370(T) adapters work with Mendocino chips. And in theory you could use a 370(M) slotket and then an interposer to go to Coppermine configuration...
# 370(T) can be slotket (PowerLeap PL-iP3/T includes VRM), slotket + interposer, modded slotket, slotket + modded CPU.
## 370(T) can be interposer, modded slotket, modded CPU.

Slot 1 to 370(C) slotkets are pretty normal, but there are also more exotic converters, such as the Powerleap Neo S370 (370(M) to 370(C)), UpgradeWare Slot-T (Slot 1 to 370(T)), Lin-Lin 'Converter Slocket' and PowerLeap PL-370/T (370(C) to 370(T)).

A word on BIOS support

It seems BIOS compatibility is also hit or miss. Some boards might reject unknown CPUs, others (like mine) might just show the incorrect name. For Award BIOSes there's a patcher that adds microcode updates and makes a BIOS support extra CPUs. Of course, for my Compaq-specific BIOS that's a no go. Thankfully, by board isn't difficult about processors it doesn't know, though of course it won't have microcode updates for them.

High-end processors

High-end CPU examples
FSB (MHz)VoltageSocketCPU
100~2.0Slot 1P3-600 (Katmai)
100~1.7Slot 1P3-1000 (Coppermine)
100~1.7370(C)Celeron 1100 (Coppermine)
100~1.7370(C)P3-1100 (Coppermine)
100~1.5370(T)Celeron 1400 (Tualatin)
100~1.5370(T)P3-1400-512 (Tualatin) @ 100*10.5=1050
133~1.7Slot 1P3-1900 (Coppermine)
133~1.7Slot 1P3-1133 (Coppermine) (recalled?)
133~1.7370(C)P3-1100 (Coppermine)
133~1.7370(C)P3-1133 (Coppermine)
133~1.5370(T)P3-1400-5112 (Tualatin)

My upgrade

I didn't want to go for Tualatin at once, as it would mean buying a relatively expensive (modded) chip. I started out with an MSI-6905 Master v2 slotket and a cheap Coppermine Celeron 1000.

Although some 440BX based motherboards support FSB speeds higher than 100MHz, mine does not. That means the 1GHz Slot 1 Coppermine CPU would be a nice, easy upgrade candidate. However, high-end Slot 1 processors are much more expensive than similar Socket 370 models. Why? Probably fewer of them made, and the 'best' model of a certain hardware family always commands a premium.

PLL specs
Stuck with 100MHz with my PLL.
Although it wasn't on my shortlist, I ended up going with a 1GHz Coppermine Celeron, as it's a 100MHz FSB Coppermine I could easily get for cheap. There's also a 1.1GHz model, and an 1.1GHz P3 would have definitely been nicer, but I couldn't find them for sale, at least not for a fair price.

coppermine bios
coppermine cpuz
Coppermine detected by BIOS and by CPU-Z.

Once the Coppermine chip was proven to work, I used eBay to order a Tualatin P3-1400S from Korea; a guy there sells them with a built-in interposer to make them work with Coppermine boards. The chip was detected fine, although it obviously runs at 1050MHz (100x10.5). However, from what I've read it should (mostly) be faster than a Celeron 1400, I can use it if I get a 133MHz FSB board in the future, and running the CPU at a lower speed will mean less stress on the current motherboard.

Tualatin 1400MHz with interposer.
tualatin bios
Tualatin detected by BIOS and by CPU-Z.

My MSI-6905 Master v2 slotket is easy to find and good. It includes a bus voltage clamp chip, which is nice. Strangely, the jumpers match this datasheet while the photos of the board don't have a clamp chip; in this datasheet the photos more closely match, yet the jumpers don't.

Not a problem: VRM

As the tables state, your motherboard's VRM needs to support the lower voltages required by more modern CPUs. If not, you need an expensive and hard to find slotket that includes its own VRM. I was in luck. My motherboard had a 'CS5159' VRM. The datasheet was easy to find and it's a VRM 8.4 compatible chip; even supports voltage low enough for Tualatin! Suprising, as this is a Slot 1 office PC. Note, however, that some Tualatin processors use 1.475v, while my VRM only provides voltage in .05v increments. This isn't a big deal.

VRM specs
VRM specs.

CPU voltage can be measured at a MOSFET near the VRM - it's the voltage between the MOSFET's tab and ground. I measured that with my slotket set to Auto voltage, correct voltage was delivered to the Coppermine Celeron. On my motherboard I measured 1.5v with the Tualatin in Auto mode, although I thought it would give it 1.45v. Especially since I run the Tualatin at a lower speed I could probably use the slotket's jumpers for an even lower voltage, but I'd rather not mess around with that.

Not a problem: MOSFets

Both Katmai and Tualatin CPUs pull about 32W, but a Tualatin will do so at a lower voltage. That means higher current. The Katmai will pull 16A, the Tualatin 22. Thankfully my board's F76132P MOSFETs can take 76A. They have an internal resistance of .011 Ohms. This means the power dissipated in the FETs goes from 16*16*0.011=2.8W to 22*22*0.011 to 5.3W. Thankfully, they already have a heatsink. Of course, the board's traces will also have to deal with the higher current. The heatsink doesn't get warm with the Coppermine Celeron at full load, nor does it with the Tualatin P3-S.

Problem: Not enough space for a Socket 370 cooler

By default the Deskpro EN SFF has no space left above its passively cooled Slot 1 CPU. A slotket with on top of that a Socket 370 heatsink and fan would be significantly taller. As I was only using an SSD, no floppy or hard drive, I decided to get rid of the standard drive tray and 3D print a tray for just the SSD. I also printed a blanking plate for the floppy drive slot.

stock deskpro case
No space for a taller CPU cooler.
new SSD mount
The new SSD tray leaves plenty of space.
floppy drive blanking plate
Blanking plate for floppy drive slot.

Problem: Cooler handle fouls on SSD

The next problem was that the (pretty nice) handle on the clamp for my cooler just touched the SSD's SATA to IDE converter PCB. Hadn't seen that one coming. Solved by fitting another clamp from my junk drawer.


Problem: CPU Fan header doesn't work

For some reason the fan header in this system has the ground and RPM pins swapped. Easily fixed by swapping the pins in the fan's connector. Unfortunately I haven't been able to actually read the fan speed.

Problem: Slotket sits loose

My slotket didn't come with any retaining hardware / backing plate, but I doubt it would have fitted in this system anyway. I printed a simple brace that keeps the slotket from flopping around in its slot.

3d printed parts
All 3D printed parts - the one in front fixates the slotket.

Problem: Fan is noisy

Maybe I could have kept this system passively cooled - the heatsink doesn't even get warm to the touch. However, adding a Noctua low-noise adapter (i.e. resistor) worked well enough.

end result
The end result.


Some benchmarks. I also tried a Coppermine P3-1000 @ 750 MHz.

PCMark2002 results
PCMark2002 results
PCMark2002 results
PCMark2002 results
Tualatin in separate chart due to huge difference...
PCMark2002 results
PCMark2002 results
Tualatin in separate chart due to huge difference...
PCMark2002 results
PCMark2002 results
This benchmark shows that its data doesn't fit in the Celeron's cache. Tualatin in separate chart due to huge difference...
Created: Jun 30 2020
Modified: Aug 05 2020