Mobile CPU in a desktop MB - Intel only revolution?

[paulsiu]

A lot of excitment have been generated by the Pentium M chip being used in desktops, especially in HTPC where silent and cool running is a desired feature. However, the Pentium M isn't socket compatible with anything else and the Pentium M boards cost a bundle. Why isn't there an AMD alternative?

Why haven't a simiar revolution been started on the AMD side? I am not starting a Pentium vs AMD war here, but just speaking pragmatically. Mobile Athlon XP and Athlon 64 are pin compatible with their desktop siblings. A lot of boards can run the mobile processor with a BIOS upgrade. There are a good number of folks who run mobile Athlon XP these days in their desktop motherboard. They are also popular with overclockers because you can OC a mobile to a higher speed.

Yet, support for AMD mobile processors have been weak. The BIOS may support it, but none or few motherboard manufacturers list mobile processors on their cpu support list. Compatiability have been verified only through some brave soul's trial and error. When do you think that this will change? Why haven't any AMD MB manufacturer attempted to break into this untapped market?

Paul

[sthayashi]

You've lost me on the complaining. I was under the impression that, at least on the XP side, most motherboards could handle mobile processors. I know that I did without a BIOS upgrade.

The Athlon 64 side, you may be right. I haven't much recently around here about people putting mobile A64s into their desktop motherboards. I suspect it's partially because of 2 things:
1) Cool 'n Quiet can do some amazing power reductions. I think that at idle w/ CnQ enabled you can actually get power draw comparible to the Pentium-M. A comparison is being prepared and studied by SPCR as we speak and an article on the subject is coming soon .
2) 90nm Athlon 64s are suprisingly power efficient. Only available on the 939 socket, they consume less power than their 130nm brothers but produce the same performance speeds.

AMD IS rumored to be coming out with a Pentium-M competitor, called the Turion, I believe. Watch for that in coming months.

[Rusty075]

The reason you don't see AMD-mobile specific motherboards is that there's no demand for them. In Intel-land, the development of the mobile-desktop boards was driven by the fact that there were no boards on the market that could put the mobile chips into a desktop setting. With AMD, the fact that the mobile CPU's are compatible with existing motherboards means there no drive to develop mobile-only boards.

While XP-M and A64-M compatibility isn't universal, ther are enough boards, with enough features, to satify the market. There are dozens of motherboards to choose from, at prices from <$40.

With regard to putting low-power chips into the desktop market, AMD is still ahead of Intel, even with the P-M starting to show up.

[kamina]

I don't understand the reason for complaint. The 90nm winchester cpu's run almost as cool as the pentium -m, and you don't have to pay a premium. Why would they push mobile cpu's on the market?

Intel has a complete other problem. Their pentium -4 processors pump out up to 4 times more heat then the pentium -m, hence they might be motivated to bring an alternative to the market. Even in this situation they don't seem like they are working hard to do it though. The motherboards cost triple what a normal motherboard would, and processors are not cheap.

Amd is clearly moving towards socket 939 on desktop products, and mobile processors are socket 754. I really don't see any problem in cooling down the new amd's desktop products though.

[paulsiu]

The 90 nm A64 are very nice, but Pentium M still draw about 1/3 the power of a 90 nm A64 at idle and at max load. 90 nm A64 are rated at around 65W. Mobile Athlon XP are rated anywhere from 25 to 45W. Pentium M is at around 21 watt.

Direct support for mobile Athlon XP and 64 on desktop motherboard are actually quite rare. Look through any manufacturer's compatibility list and you will not find any mobile cpu's in the list. Getting them to work is a matter of luck. Someone has to plug a cpu in and find out if it will work. Sometimes, there's voodoo involve in flashing the bios with a desktop processor before you can upgrade to the mobile one.

I just think that mobile cpu would be a nice route to go for those who want quiet under load. Cool and Quiet is nice, but what good is it if your machine gets noisy underload. Most HTPC folks already spend premium for their case and they tend to like small cases, which translate to heat issues. Why not spend some money on a cooler processor? In addition, since mobile cpu uses socket 754, this may be a nice way to extend the life of some of the old motherboards.

[burcakb]

I very much doubt that Athlon64-M s are anything other than your standard A64 without the spreader and tested to undervolt.

Try undervolting your regular A64. You should get pretty much near mobile power draws.

[sthayashi]

I just think that mobile cpu would be a nice route to go for those who want quiet under load. Cool and Quiet is nice, but what good is it if your machine gets noisy underload. Most HTPC folks already spend premium for their case and they tend to like small cases, which translate to heat issues. Why not spend some money on a cooler processor? In addition, since mobile cpu uses socket 754, this may be a nice way to extend the life of some of the old motherboards.

Dude, you're preaching to the choir with me. Socket 754 will eventually be turned INTO a mobile-only socket (at least according to the rumors). And as for motherboards getting to work with mobile processors, like I said, for the XP line they usually just work. You complain about BIOS upgrade as though it were a bad thing, but how often did a motherboard need a BIOS upgrade when processors changed internals (i.e like the move from Palomino -> T-bred -> Barton). Every single one required a BIOS upgrade, and in some cases, the higher up Barton series were not necessarily advertised on the motherboard marketing. Generally, people didn't care because motherboard technology increased alongside processor technology. So when you decided to upgrade to Barton, chances are, you decided to upgrade to a motherboard that was capable of 200MHz FSB.

A mobile CPU IS the nice route to go for people who want quiet under load. I'm typing this up on a Mobile XP 2600+. But here's the real kicker. The mobile versions of XPs & 64s are nothing but undervolted versions of their non-mobile counterparts. Why pay a premium on the 'mobile' labeling when you can just make it act like a mobile yourself?

EDIT: By the way, I'm moving this to the Silent Front. I think this discussion is more appropriate in that forum.

[Chris`I]

I was under the impression that Mobile AMD chips are hand picked normal stock chips that can be run at much lower voltages. I dont know what a mobile XP will go down to, but my XP2500+ (t'bred) is quiet happy sitting on 133FSB @ 1.125v totally stable (tested with prime95).

As the guys say, there is no needed "special" boards for the mobile chips as they are supported by normal mobos as they are normal chips just hand picked. Pretty sure thats the same case with the new A64s.

sthayashi: what kind of speeds can you get at which voltages? Just for comparison.

[sthayashi]

sthayashi: what kind of speeds can you get at which voltages? Just for comparison.

I generally operate at 2 settings and I'm not too sure how optimal they are:
2.0GHz @ 1.35v (167 FSB)
1.2GHz @ 1.1v (100 FSB)

I use 8rdavcore to choose my setting, whether I need 2.0GHz for encoding music, or if I can get by with 1.2Ghz just browsing, listening to music, or not doing anything at all. My motherboards appears to report a slightly lower voltage than what was specified though.

[yeha]

The 90 nm A64 are very nice, but Pentium M still draw about 1/3 the power of a 90 nm A64 at idle and at max load. 90 nm A64 are rated at around 65W. Mobile Athlon XP are rated anywhere from 25 to 45W. Pentium M is at around 21 watt.

true, the a64 winchesters are rated for 67W, but that is the maximum value that any cpu in the winchester product line may put out, now or in the future. so, they were leaving themselves headroom for 3800+, 4000+, etc. cpus that may have been brought out with that core.

most trial-and-error tests that have been performed show that the 90nm a64 chips consume ~35W for speeds between 1800 and 2200 mhz (3000+ -> 3500+). i haven't seen anyone write up a definitive test of power consumption (i.e. 3x3 table of psu draw at 1.8, 2.0, 2.2 ghz and 1.1, 1.25, 1.4 volts, just so we're sure of the figures we calculate).

[Chris`I]

sthayashi: what kind of speeds can you get at which voltages? Just for comparison.

I generally operate at 2 settings and I'm not too sure how optimal they are:
2.0GHz @ 1.35v (167 FSB)
1.2GHz @ 1.1v (100 FSB)

I use 8rdavcore to choose my setting, whether I need 2.0GHz for encoding music, or if I can get by with 1.2Ghz just browsing, listening to music, or not doing anything at all. My motherboards appears to report a slightly lower voltage than what was specified though.

Looks like your chips is better at higher speeds for lower power, but at the lower end mine is very similar, I get

2.0GHz @ 1.5v (190 FSB)
1.3GHz @ 1.125v (133 FSB)

Was just wondering if it was worth getting a Mobile chip as I use that machine for my TV as well. At 1.125v the w/c loop runs fanless, so I dont think theres any reason to splash out for a mobile chip, as it runs no lower at that speed.

Thanks

[paulsiu]

OK, so mobile A64 are basically undervolted desktop. I thought there were some differences like the missing heat spreader and better stepping.

In any case, has anyone undervolted the older 130 nm A64's? My broad uses socket 754 so I can't use the newer 90nm.

What's the downside of undervolting. Suppose I get a 3700+ A64 and undervolt that. Do I need to drop the clock speed as well? Will this vary from chip to chip?

Paul

[NeilBlanchard]

Hello Paul:

Sure, I undervolted an Athlon 64 2800+ S754 on an AOpen motherboard, down to 1.35 volts. It ran totally stabily for a week (remember, undervolting is kinda' like overclocking in reverse), but since I was delivering it to a client, I bumped it up to the next level, 1.375v -- it still ran a good 6C or 8C cooler than stock -- it got up to 40-42C under 100% load. That was with the Alpha cooler and a thermally controlled Enermax fan. The fan ran at minimum speed -- or it was off at idle! Pretty cool.

[sthayashi]

Looks like your chips is better at higher speeds for lower power, but at the lower end mine is very similar, I get

2.0GHz @ 1.5v (190 FSB)
1.3GHz @ 1.125v (133 FSB)

Was just wondering if it was worth getting a Mobile chip as I use that machine for my TV as well. At 1.125v the w/c loop runs fanless, so I dont think theres any reason to splash out for a mobile chip, as it runs no lower at that speed.

Thanks

Well, I can kick it down a lot lower, but that doesn't happen dynamically. There have been times when my motherboard or BIOS decided that the multiplier shouldn't be 12x, but 6x. So I've actually run this at 600MHz @1.1V. It doesn't really save that much power. But it gets really annoying trying to do audio encoding then.