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The Pentium M on the desktop: DFI's 855GME-MGF


DFI's 855GME-MGF motherboard
— 2:31 AM on February 2, 2005

ManufacturerDFI
Model855GME-MGF
Price (street)
AvailabilityNow

THE STARS WERE perfectly aligned for this to happen. Since making the move to a new 90nm fabrication process, the Pentium 4 processor has been struggling mightily. Compared to the previous generation, Pentium 4 "Prescott" chips run hotter, consume more power, do less work per clock cycle, and have had a difficult time reaching higher clock speeds that might offset their performance disadvantages.

Their SAT scores are lower, too.

Prescott's weaknesses have prompted an abrupt change in direction at Intel. Most fundamentally, the company's faith in one of the corollaries of what used to be called Moore's Law has apparently been shaken. Ever-higher clock speeds are no longer a given. The 4GHz version of the Pentium 4 was slated to appear before the end of 2004, but Intel axed those plans. The company has instead introduced a new model numbering system that deemphasizes clock speeds and focused its future developments on dual-core versions of its processors.

Meanwhile, silent computing and small form factors are on the rise in desktop systems, as consumers become more aware of PC features beyond raw performance. Against this backdrop, certain corners of the market have fixed their gaze firmly on a tantalizing alternative: the Pentium M processor, optimized to deliver solid performance combined with miserly power consumption, that has seen great success in the mobile market as part of the Centrino platform.

Now comes DFI with exactly what we've been asking for: a desktop motherboard for the Pentium M. The DFI 855GME-MGF transcends boundaries by offering Pentium M support in a microATX mobo with an AGP slot and some decent overclocking options. But can the Pentium M really go toe to toe on performance with the Pentium 4 and Athlon 64 when paired up with desktop hard drives and video cards? We've gathered up a Pentium M "Dothan" processor and an extensive array of competitors, ranging from an Athlon 64 3200+ at 2GHz to a Pentium 4 at 3.8GHz, in order to find out.

The motherboard
DFI's ever-so-snappily named 855GME-MGF is an unassuming microATX-sized desktop motherboard with a more or less complete slate of slightly dated options, including AGP, PCI, and PCI-X slots, but no PCI Express. The board itself is wears a handsome black color and sports passive coolers for the north and south bridge chips.


The DFI 855GME-MGF

You can see most of the important bits in the photo there, but you'll have to squint. Let me drop the specs on you to save you the eyestrain.

CPU supportmPGA479M Intel Pentium M/Celeron M processors with 400MHz front-side bus
Form factormicroATX
ChipsetIntel 855GME
North bridgeIntel 855GME MCH
South bridgeIntel 6300ESB ICH
InterconnectIntel Accelerated Hub (266MB/sec)
Expansion slots1 AGP 8X
2 32-bit/33MHz PCI
1 PCI-X
Memory2 184-pin DIMM sockets
Maximum of 2GB of DDR333 SDRAM
Storage I/OFloppy disk
2 channels ATA/100
2 ports Serial ATA 150 via 6300ESB south bridge with RAID 0,1 support
Audio6-channel HD audio via 6300ESB integrated audio and Realtek ALC655 codec
Ports1 PS/2 keyboard
1 PS/2 mouse
1 serial with header for 1 more
1 parallel
1 VGA
4
USB 2.0
1
 IEEE 1394 port via VIA VT6307 Firewire controller
     with header for 1 more
1 RJ45 10/100/1000 Gigabit Ethernet via Realtek 8110S-32

1 line out/front out
1 mic in/center-sub out
1 line in/rear out
1 SPDIF out header (internal)
BIOSPhoenix AwardBIOS
Bus speeds100-250MHz in 1MHz increments (400-1000MHz quad-pumped)
Bus dividersLocked PCI speeds of 33, 36, 40MHz plus ratio options
VoltagesCPU: 0.7V to 1.34V in 0.016V increments
DRAM: No manual control
North bridge:
No manual control
MonitoringVoltage, fan status, and temperature monitoring
Fan speed controlNo manual control
The mobo is limited somewhat by the Pentium M processor and by Intel's 855GME chipset, which is now being replaced in newer Centrino laptops by a mobile version of the 915 chipset with support for PCI Express, DDR2 memory, HD Audio, and a 533MHz front-side bus. The 855GME's front-side bus officially tops out at 400MHz, and its single channel of DDR memory won't reach past 333MHz without overclocking—not exactly the stuff of legend. The motherboard is pretty well appointed, though, with a Gigabit Ethernet chip and six-channel audio (although both are based on relatively inexpensive Realtek chips).

Overclocking the bejeezus out of the Pentium M
Fortunately, DFI has given the 855GME-MGF a handful of key overclocking options, including adjustments for the front-side bus speed (purportedly up to 1GHz, although the practical limits seem to be much lower than that) and the CPU multiplier. Yes, thanks to the Enhanced SpeedStep clock throttling mechanism, retail Pentium M processors come with unlocked lower multipliers. This fact interlocks nicely with the DFI mobo's support for a 533MHz front-side bus and its clock lock for the AGP and PCI busses.

In testing, I was able to get my retail Pentium M 755 CPU, whose stock speed is 2GHz, running stable all day long at 2.4GHz on a 533MHz bus. In fact, the system was wholly stable on the first try, with very little drama. The CPU darn near ran at 2.53GHz, as well. I could get it to boot into Windows and run deep into 3DMark05 before crashing, but I never could achieve 100% stability at 2.53GHz. I suspect I might have had more success if the DFI board could push the CPU voltage one or two steps past its 1.34V limits. The DFI board also lacks voltage adjustments for system memory and the north bridge, so it's not an ideal overclocker like the boards in DFI's LANParty line.

In part due to the RAM voltage limitations, I decided to keep the DIMM speed at a 4:3 ratio to the PCI/AGP clock, yielding a (roughly) 178MHz memory clock, or 356MHz once you take DDR memory's clock-doubling mojo into account. With more juice to the RAM and more relaxed timings, the memory might have tolerated a 5:3 ratio and its corresponding 221MHz clock speed. Without extra juice, the system wouldn't POST with the RAM at 221MHz, even with relaxed 2.5-3-3-6 timings.

Nevertheless, the 855GME-MGF overclocked the Pentium M easily and efficiently to 2.4GHz while keeping the AGP/PCI bus speeds in spec and allowing me to drive the RAM faster than the chipset's usual 333MHz limit. That's pretty smooth, all things considered.


DFI's Pentium M cooler is just a little bigger than the north bridge cooler

All of this overclocking activity was taking place, by the way, using DFI's relatively dinky cooler for the Pentium M. This cooler is a custom job included in the box with the motherboard. The cooler screws into a plate that has four screw holes and goes under the motherboard. Unfortunately, this cooler is likely your only option. AOpen makes a competing desktop Pentium M board that will accept larger, more capable Socket 478-style coolers, but there's not enough clearance around the CPU socket on the DFI board for such things. As it stands, DFI's cooler has a low enough profile to fit into many a slimline case for home theater PCs, and the board's built-in Intel graphics might allow one to get away without a video card, so long as the drab combination of minimal 3D acceleration and a VGA output is acceptable.

Of course, things get more interesting when we fill up that AGP slot with a fast graphics card and compare the Pentium M to some desktop processors, which is what we're about to do.