Do you need horsepower or just efficiency? As already said, some kind of highly integrated more modern low-voltage platform with the required compatibility will likely be the best.
Once you start going into sub-50W machines, power supply plays a role too as typical ATX units' efficicency drops veeeeery rapidly at low loads. With smaller modern units you need to pay attention to the 5V rating too.

Assuming 86% efficiency at 10-15% load, I've emeasured PIII 866, GF3, 2x 80GB spinning rust requires 65W in these applications.
https://streamable.com/3ngfo7

Sombrero wrote on 2023-07-13, 03:05:

I'll see how well that CPU undervolts. If it doesn't undervolt well enough to run it passive I might go and find a 500MHz/100MHz Coppermine and have a go with that. The Noctua fan I've got in there with a NA-RC12 low noise adapter isn't exactly loud but you can't beat no noise at all.

@gerwin looks like you were absolutely correct!

Went straight to 1.3V and ran Prime95 four hours with no issues whatsoever, I call that stable enough. Too bad the motherboard doesn't allow even lower voltage, seems to me the cpu might be fine with Vcore under 1.3V.

Power draw from the wall dropped around 8-9W according to my watt meter and temps dropped around 4°C, which is less than I expected. Can't still comfortably go passive without getting a bigger heatsink and I'm not sure the 500MHz/100MHz P3 would be any different, so I'll keep things as they are for now.

Well... my laptop has a 5.5W Pentium M (1.1W idle), a 6W Mobility Radeon 7500 (1.6W idle), and 1.8W 855PM chipset. Since Win98 can't take advantage of multiple cores on newer CPUs, Pentium M seems like a good choice in theory. There are a few motherboard options for building a desktop Pentium M system, not too many though unfortunately. With the power consumption being so low, they can run off a flex-ATX PSU.

A 440BX board that supports voltages < 1.8, a slotket with voltage configuration jumpers, and a Via C3 Ezra might be an interesting alternative too.

The 1GHz / 100MHz FSB Ezra is specified to ~10W TDP, and is roughly equivalent to a 500MHz P3 in performance. It can also be tuned in very small steps from everything between 386 and the aforementioned performance with software like Setmul, which in my opinion makes it even better than the classic K6-2/3+ setups for flexibility.

The only downside is that sourcing the right mobo is going to take some research, and if you're unlucky, some BIOS hacking. It'll not work with any old 440BX board.

Personally if I wanted low power win98 pc I would go for K6 III+/atz400 1.6V cpu since there are powernow! drivers for win98 for multiplier change when idle and if it is for gaming I would add a voodoo 3 into that since you cant avoid some power usage when you are actually playing games on it. Since the L3 cache on motherboard does not matter really you could disable it for little bit of power save too.

Wow apparently there's much interest in this subject. Not trying to set a record here though. This is a PC that is only on when gaming and I just wanted to get away from mainly p4 and athlons because its not easy to find one significantly below 60W, and also high-end cards that draw too much power, like some FX, etc.
The initial configuration sounded like a good starting point, but I will take a look at the geforce2 MX line, and all the other contributions. A centrino based laptop with geforce go also seems like a decent choice. Thanks

bakemono wrote on 2023-07-13, 10:35:

Well... my laptop has a 5.5W Pentium M (1.1W idle), a 6W Mobility Radeon 7500 (1.6W idle), and 1.8W 855PM chipset. Since Win98 can't take advantage of multiple cores on newer CPUs, Pentium M seems like a good choice in theory. There are a few motherboard options for building a desktop Pentium M system, not too many though unfortunately. With the power consumption being so low, they can run off a flex-ATX PSU.

Can you please share the model? Laptops have much more efficient psu.

A001 wrote on 2023-07-13, 10:00:

Do you need horsepower or just efficiency? As already said, some kind of highly integrated more modern low-voltage platform with […]
Show full quote

Do you need horsepower or just efficiency? As already said, some kind of highly integrated more modern low-voltage platform with the required compatibility will likely be the best.
Once you start going into sub-50W machines, power supply plays a role too as typical ATX units' efficicency drops veeeeery rapidly at low loads. With smaller modern units you need to pay attention to the 5V rating too.

Assuming 86% efficiency at 10-15% load, I've emeasured PIII 866, GF3, 2x 80GB spinning rust requires 65W in these applications.
https://streamable.com/3ngfo7

Both. The most balanced between horsepower and efficiency. I would be happy if the whole system, including monitor and speakers would draw max 60W. Unfortunately that seems to be what an athlon or P4 cpu draws, hence the 18W coppermine and the voodoo3.

Some Athlon XP CPUs can be underclocked to very low power and Geode variety are already minmaxed to low TDP. Early Pentium 4s are less interesing, can't change CPU multiplier directly, only through throttle.

Sombrero wrote on 2023-07-12, 18:21:

That 1.3V something Coppermines can generally really hit? Seems pretty drastic amount to undervolt from 1.6-1.75V to 1.3V.

But if that is actually something you can realistically hit I'll take it, less heat = quieter fan and I'm all for that.

Yeah, it's possible. 1Ghz Coppermine, provided you have lucky silicon, can work at ~1.4v without any underclocking.

Sombrero wrote on 2023-07-13, 10:09:

@gerwin looks like you were absolutely correct!

Went straight to 1.3V and ran Prime95 four hours with no issues whatsoever, I call that stable enough. Too bad the motherboard doesn't allow even lower voltage, seems to me the cpu might be fine with Vcore under 1.3V.

Power draw from the wall dropped around 8-9W according to my watt meter and temps dropped around 4°C, which is less than I expected. Can't still comfortably go passive without getting a bigger heatsink and I'm not sure the 500MHz/100MHz P3 would be any different, so I'll keep things as they are for now.

Thanks for the detailed report. I was already guessing an 8 Watt drop, but never measured it myself. Note that the lowest multiplier on a retail Coppermine is 4.0x, which can be set at 266MHz (66x4.0). So that is the lowest, and upwards there are many options to choose from.

As for this topic in general. I have two Mobile on Desktop Mini-ITX boards, Like what AOpen sold as "MoDT" boards. Intel Socket M and Socket P. Also a Mini-ITX socket 1155. Maybe the oldest Socket M one could be somewhat succesful with Windows 98, but I ran XP on it instead. I have a bunch of uncommon mobile processors for the two MoDT boards that I want to tinker with in the future. Even the slowest "Core Solo" model 😉.
That is what I did investigate, lower power systems that could still run Windows XP well. In that regard it is hard to beat a nettop like this Foxconn nt-a3500 with AMD E-350. I use one as my internet-radio and movie player. I would have liked slightly more CPU power, but Windows XP drivers were dropped in later hardware.

NostalgicAslinger wrote on 2023-07-12, 18:10:

cyclone3d wrote on 2023-07-12, 17:58:

What is the reasoning behind wanting a super low wattage Windows 98 machine?

Countries like Germany have very high energy prices because of the Ukraine war, so I can understand that.

It's around 40 Cent/kWh. So if the system including monitor (which is a significant part of the calculation) draws 100 Watts that's 4 ct per hour. Nothing I worry too much about 😀

Any laptop is probably the most efficient way to go. When using a desktop then go for a small LCD monitor.

If anyone has one of those pink things that Linus just reviewed, should see if 98 goes on it 🤣

The Serpent Rider wrote on 2023-07-13, 12:38:

Some Athlon XP CPUs can be underclocked to very low power...

Regarding Athlon XP:
There was a tool back in the days called "S2kCtl"
https://web.archive.org/web/20070209083504/ht … targaz0r.nm.ru/
that perfomed a bus disconnect which greatly reduced the power consumption.

Bus disconnect is pretty much pointless for system of that kind. Idle time should be minimal anyway.

For modern low power desktop computer for light computing and web gaming, web browsing, I recommend HP Mini series. You can change CPU for 35W instead of 45W or 65W, newer ones takes *Two* NVME M.2 SSDs.

But remember, if you going to use windows 11 now or in future and efficient, then must get HP elitedesk 800 G5 Mini that uses one of these 9th gen CPUs. I have one running i5-9500 (65W) with 32GB and 1TB NVME and one slot left for second NVME SSD. There are two types of Minis. Easiest way to tell apart is vented top cover means this Mini utilizes copper heatsink and up to 65W CPUs. The ones with no vents can only take up to 45W and heatsink is aluminum.

What more, windows 7, 8 and 10 COA keys internal to these HP any computers can activate windows 11. Confirmed with my Mini was for 10 Pro. Activated the 11 Pro no problem. Big saving on paying for a COA.

Cheers,

1541 wrote on 2023-07-13, 18:02:

Regarding Athlon XP: There was a tool back in the days called "S2kCtl" https://web.archive.org/web/20070209083504/ht … targaz0r. […]
Show full quote

The Serpent Rider wrote on 2023-07-13, 12:38:

Some Athlon XP CPUs can be underclocked to very low power...

Regarding Athlon XP:
There was a tool back in the days called "S2kCtl"
https://web.archive.org/web/20070209083504/ht … targaz0r.nm.ru/
that perfomed a bus disconnect which greatly reduced the power consumption.

You can downclock and unvervolt K8 line of cpus also, even in pure dos, slowest Mobile Sempron or Turion64 should do 800-1600Mhz .

There are other cpu dos tools as well.
For K8, look A64LOWP 1.1 and LOWP 1.0
http://falcosoft.hu/dos_softwares.html

Confused UngaBunga wrote on 2023-07-13, 12:29:

bakemono wrote on 2023-07-13, 10:35:

Well... my laptop has a 5.5W Pentium M (1.1W idle), a 6W Mobility Radeon 7500 (1.6W idle), and 1.8W 855PM chipset. Since Win98 can't take advantage of multiple cores on newer CPUs, Pentium M seems like a good choice in theory. There are a few motherboard options for building a desktop Pentium M system, not too many though unfortunately. With the power consumption being so low, they can run off a flex-ATX PSU.

Can you please share the model? Laptops have much more efficient psu.

This is a Japanese model NEC VersaPro VY10F/BH-L. IIRC, there was also a BH-R that was similar, and a BH-M with touchscreen? And VY80... something that had a Celeron M instead of Pentium M. There was an overseas version with English keyboard layout called Versa S820. I should also note that the original CPU was 6.4W (Banias, 130nm) but mine was upgraded after the fact for a small performance boost.

HanSolo wrote on 2023-07-13, 17:02:

It's around 40 Cent/kWh. So if the system including monitor

40 cents is a lot, I would never pay that much. The last 10 years I have paid max. between 6 and 10 cents.

You could make a solar powered setup

NostalgicAslinger wrote on 2023-07-15, 15:00:

HanSolo wrote on 2023-07-13, 17:02:

It's around 40 Cent/kWh. So if the system including monitor

40 cents is a lot, I would never pay that much. The last 10 years I have paid max. between 6 and 10 cents.

But not in Germany 😀 15 years ago it was already around 20 ct, and slowly rising. The 40 ct (and even up to 70) was because of the war in Ukraine. The average price for new contracts is now lower again (30 or so), but people usuablly have 1 year contracts.

My point was: even at 40 ct/kWh I wouldn't worry about the costs of my retro system which is probably used only few hours per week.