Shuttle’s XPC SN25P mini-barebones system

Sporting a 939-pin socket for the Athlon 64, an nForce4 chipset, PCI Express, and an integrated Envy24PT audio controller, the XPC SN25P could be the best small form factor barebones system to date. Does it deliver on its considerable potential? Was it worth the wait? Read on to find out.

The specs
We’ll kick things off with a look at the SN25P’s spec sheet. Right off the bat, notice that the system is based on NVIDIA’s vanilla nForce4 core logic chip, not the Ultra or SLI versions.

What differentiates the nForce4 from its Ultra cousin? Surprisingly little. When employed in Socket 754 motherboards, the vanilla nForce4’s HyperTransport link is supposed to be limited to 800MHz. That’s not an issue for the Socket 939 SN25P, though. The system’s nForce4 HyperTransport link runs at 1GHz, just like the Ultra’s.

On the storage front, the vanilla nForce4 lacks the Ultra’s support for 300MB/sec Serial ATA II transfer rates, but that’s hardly worth shedding a tear over. Serial ATA II drives aren’t available yet, and while short burst transfers may be able to take advantage of some of the extra bandwidth, even today’s fastest 15K-RPM SCSI hard drives can’t sustain transfer rates that would saturate Serial ATA’s 150MB/s pipe. Apart from the lack of 300MB/s transfer rates, the nForce4’s storage and RAID capabilities are identical to the Ultra’s, so you’re not missing much.

The only other feature that the nForce4 lacks is ActiveArmor acceleration for the chipset’s integrated Gigabit Ethernet controller and firewall. The GigE controller and firewall are still there, just not the hardware acceleration, which could result in higher CPU utilization during network transfers.

The nForce4 doesn’t differ from its Ultra brethren at all when it comes to integrated audio. Both offer generic AC’97 audio without hardware acceleration or support for high definition resolutions and sampling rates. Fortunately, Shuttle completely bypasses the nForce4’s integrated AC’97 sound in favor of VIA’s Envy24PT audio controller. The Envy24PT doesn’t have hardware acceleration, but it does support higher sampling rates and resolutions. Considering the SN25P’s lack of a PCI slot and the scarcity of PCI Express sound cards, it’s nice to see Shuttle making an effort to compensate for the nForce4’s anemic integrated audio.

Outside the box
As you might expect, the SN25P’s exterior is similar to other P-series chassis. Shuttle mates the cube’s deep charcoal body with a blue face plate and silver trim to lighten the mood, making for an attractive aesthetic that’s still reserved enough for the office.

Like other P-series systems, the SN25P integrates a memory card reader right up front. The card reader consumes two of the chipset’s USB ports, but given the popularity of digital cameras, those are ports well spent. Shuttle hides the rest of the system’s front panel goodies under a series of drop-down doors.

With the touch of a finger, the doors swing down to reveal an external 3.5″ drive bay and a front port cluster that includes audio, USB, and Firewire plugs.

Shuttle also hides the SN25P’s 5.25″ drive bay behind a stealthy door, keeping beige optical drives from scarring the system’s otherwise attractive face. The spring-loaded door opens and closes automatically under the force of the optical drive tray. The chassis is also equipped with an adjustable external eject button that’s compatible with a wide range of optical drives.

Moving to the side of the system, we catch a glimpse of the P-series’ Prescott roots. This chassis was originally designed for toasty Prescott Pentium 4 processors, so the chassis has plenty of venting to provide adequate airflow through the system.

Holes even riddle the bottom of the case, allowing cool air to waft up under the motherboard.

Oddly, the SN25P’s rear panel isn’t as heavily-vented as the rest of the cube. In fact, the grills on the system’s two 70mm exhaust fans look restrictive enough to impede airflow. The 80mm power supply exhaust fan’s grill is more open, but it’s tempting to break out a Dremel to trim some of the extra metal.

Below the fan grills, the SN25P bristles with peripheral ports. The system’s extensive array of audio ports, which includes both RCA and TOS-Link digital S/PDIF outputs, is particularly impressive. Shuttle scores points for integrating a CMOS reset button right into the port cluster, saving overclockers and tweakers from having to crack the system open to clear the BIOS.

Opening ‘er up
Enough with the outside, let’s slide off the SN25P’s aluminum shell and have a peek at what lies under the hood.

A loaded SN25P from the left…

And the right

With support for external 5.25″ and 3.5″ drives and two internal 3.5″ hard drives, the SN25P’s internals are surprisingly expansive for a small form factor system. Hard drives reside side by side along the top of the system and slide into place on a pair of very slick tool-free, snap-on rails.

The snap-on rails make mounting drives in the SN25P easier than in most full ATX systems, which is pretty remarkable. Shuttle also includes a handful of rubber bumpers to dampen vibrations between hard drives and the case’s aluminum shell. It’s a good idea in theory, but the stiff rubber bumpers are too tall for the limited clearance between hard drives and the system’s outer skin. You can force the shell back on with the bumpers installed, but that flexes the hard drive rails to a point that I’m not entirely comfortable with. Thankfully, it’s easy to trim the bumpers down to a more reasonable height.

Like the hard drive rails, the SN25P’s external drive cage is a tool-free affair. External 5.25″ and 3.5″ drives get rails of their own, and the entire drive snaps into place with nary a screwdriver in sight. With the drive cage removed, we can take a closer look at the rest of the system’s internals.

The SN25P’s PCI Express x16 slot is mounted on the outside edge of the system, leaving just enough room for double-wide graphics cards like ATI’s Radeon X850 XT and NVIDIA’s GeForce 6800 Ultra. Such cards will block the system’s PCI-E x1 slot, but until PCI Express peripherals become more prevalent, it won’t be missed.

Around the other side of the system, users have easy access to the SN25P’s DIMM slots.

The FN25 motherboard’s layout is as tight as one would expect from a small form factor system. Notice that the DIMM slots run down the middle of the board rather than along its top edge, presumably to maintain closer proximity to the Athlon 64’s on-die memory controller. Also note the use of an active chipset cooler for the nForce4, which is developing a reputation for running a little warmer than most chipsets.

Shuttle hides the FN25 motherboard’s most interesting feature up in the top corner of the board. Here, we find VIA’s Envy24PT audio controller, VT1617A codec, and a Wolfson WM8728 DAC. With support for 24-bit audio at sampling rates up to 96kHz, the Envy24PT hints at high-definition audio, but it’s not quite that easy. With analog output, codec and DAC sampling rates and resolutions also come into play, and that’s where the SN25P’s implementation falls a little short. The Envy24’s first six output channels are routed through the VT1617A codec, which only supports resolutions up to 20 bits and sampling rates up to 96kHz. The Wolfson DAC supports 24-bit/192kHz audio, but in an eight-channel configuration, it only handles channels seven and eight.

It would be wasteful just to use the high-end Wolfson DAC for channels seven and eight, but VIA’s Envy24PT drivers actually allow users to route two-channel stereo audio through the WM8728. This pipes stereo output through the SN25P’s rear 7/8 audio output, potentially offering superior fidelity to the VT1617A. At the very least, the driver switch allows users to enjoy two-channel 24-bit/96kHz audio output through analog speakers or headphones without having to worry about downsampling sapping fidelity.

Cooling and power
The SN25P ditches Shuttle’s venerable ICE CPU/system cooler in favor of dedicated cooling zones for the system’s processor, hard drives, and power supply and graphics card. Since the CPU zone is the most important one, we’ll start there.

Considering that the P-series chassis was originally designed to encase near-molten Prescott Pentium 4 processors, it’s no surprise that the chassis pays special attention to CPU cooling. The processor cooling zone consists of a shrouded wind tunnel that’s completely isolated from the rest of the system. The tunnel sucks cool air in from the right side of the system with a 70mm intake fan and expels it out the left with an 80mm exhaust fan.

A modified version of Shuttle’s ICE cooler sits between the two fans, channeling heat from the CPU up through a quartet of heat pipes into an array of tightly-packed cooling fins.

The cooler sits on a smooth copper base and screws directly into the motherboard. It’s actually the only system component that you’ll need a screwdriver to remove.

With processor cooling shrouded from the rest of the system, Shuttle can concentrate on dedicated cooling solutions for the system’s other components. The hard drive zone is cooled by a pair of 70mm exhaust fans that draw air out the rear of the system, while an 80mm PSU exhaust fan handles the graphics card and power supply zone. All three of the system’s cooling zones use temperature-controlled fans with linear speed control, which should keep noise levels to a minimum.

Given the Athlon 64’s more agreeable thermal profile, the SN25P should be able to get away with relatively low fan speeds most of the time. The Athlon 64 family’s comparatively low power consumption probably won’t tax the system’s 350W power supply, either. That should leave plenty of juice for high-end graphics cards.

The BIOS
Shuttle’s XPC BIOSes are known for giving users plenty of fan control options to balance adequate cooling with low noise levels and the SN25P’s BIOS is no exception.

Users can select from nine fan profiles, including a smart fan option that uses linear fan speed control to incrementally ramp up RPMs as processor temperatures increase. Unfortunately, the BIOS doesn’t let users set the temperature trigger point for the Smart Fan feature.

A better alternative to adding a temperature trigger to the BIOS would be for Shuttle to release a version of its XPC Tools software that supports the SN25P. However, given the fact that Shuttle’s official XPC Tools release only supports one XPC model, the SB83G, we’re not holding our breath.

As far as tweaking and overclocking options go, the SN25P’s BIOS needs some work. HyperTransport link speeds are available between 200 and 250MHz in 1MHz increments, but there’s no way to lock down the system’s PCI or PCI Express clocks, making serious overclocking a dubious prospect.

Overclockers will at least appreciate the BIOS’s CPU multiplier control, although multipliers are only available in 1x rather than 0.5x steps. The BIOS’s voltage options are a little more robust, with CPU voltages available up to 1.7V in 0.05V increments.

At first glance, the SN25P BIOS’s memory tweaking options appear to be reasonably complete. However, there’s no mention of the DRAM command rate. For that, we have to fire up A64 Tweaker in Windows.

According to A64 Tweaker, the SN25P is running with a relatively slow 2T command rate. As we’ll see in a moment, that 2T command rate can have quite an impact on performance. A64 Tweaker can actually force the SN25P’s command rate to 1T, but that has to be done manually after every reboot, so it’s hardly a practical solution. Shuttle is aware of the command rate issue and is working on a BIOS update to address it, but we have yet to receive a BIOS that can set the SN25P’s command rate to 1T.

For those who are a little shy about poking around in the BIOS, the SN25P is compatible with NVIDIA’s nTune tweaking and monitoring utility. Launching nTune produces a rather alarming warning, though.

It’s a little fuzzy, but the message warns that the system’s PCI clock is set to track the HyperTransport link. In other words, the SN25P lacks a PCI lock, at least according to nTune.

Once you get past the warning, nTune offers control over a number of system memory timings and bus speeds.

nTune can also monitor system variables, including temperatures, clock speeds, and voltages. If only it could adjust the SN25P’s fan speed profiles.

Our testing methods
Today we’ll be comparing the SN25P’s performance to that of Foxconn’s NF4UK8AA and DFI’s LANParty NF4 Ultra-D. I wouldn’t expect to see much of a performance difference between the SN25P and its nForce4 Ultra-equipped competition based on the chipset alone, but the XPC system’s lack of a 1T command rate could slow it down. Since it’s not really practical to force a 1T command rate with A64 Tweaker after every reboot, we’ve tested the SN25P with the BIOS’s default 2T command rate.

All tests were run three times, and their results were averaged, using the following test systems.

Thanks to OCZ for providing us with memory for our testing. If you’re looking to tweak out your system to the max and maybe overclock it a little, OCZ’s RAM is definitely worth considering.

With the exception of the XPC SN25P, our test systems were powered by OCZ PowerStream power supply units. The PowerStream was one of our Editor’s Choice winners in our latest PSU round-up.

We used the following versions of our test applications:

• SiSoft Sandra Standard 2005
• WorldBench 5.0
• TCD Labs HD Tach v3.01
• Futuremark 3DMark05 Build 120
• DOOM 3
• Far Cry v1.3
• Unreal Tournament 2004 v3323
• RightMark Audio Analyzer 5.4
• RightMark 3D Sound 1.24
• NTttcp
• Cinebench 2003
• Sphinx 3.3

The test systems’ Windows desktop was set at 1280×1024 in 32-bit color at a 75Hz screen refresh rate. Vertical refresh sync (vsync) was disabled for all tests. Most of the 3D gaming tests used the Medium detail image quality settings, with the exception that the resolution was set to 640×480 in 32-bit color.

All the tests and methods we employed are publicly available and reproducible. If you have questions about our methods, hit our forums to talk with us about them.

Memory performance
For our memory performance tests, we benchmarked the SN25P with both its default 2T command rate and a forced 1T command rate. This will illustrate the command rate’s impact on both memory bandwidth and latency, which should help us to understand subsequent benchmark results.

With its default 2T command rate, the SN25P lags considerably in our memory bandwidth and latency tests. Forcing a 1T command rate improves the performance considerably, although Shuttle may need to tighten additional memory timings to maximize the performance of the Athlon 64’s on-die memory controller.

WorldBench

The SN25P is only a point off the pace in WorldBench, which isn’t too bad. None of WorldBench’s individual tests stand out as being particularly problematic for the SN25P, which tends to lag by a few seconds across the board.

Gaming

With the exception of 3DMark05’s overall score, the SN25P falls behind in our gaming tests. The performance differences aren’t huge, but they’re consistent.

Cinebench rendering

The SN25P is barely slower in Cinebench…

Sphinx speech recognition

But Sphinx is much more sensitive to memory performance, and the XPC’s 2T DRAM command rate can’t keep up.

Audio performance

The SN25P’s integrated Envy25PT audio controller doesn’t offer much in terms of improved CPU utilization with positional audio, but since the Envy24 lacks hardware acceleration, that’s to be expected.

Audio quality
For RightMark’s audio quality tests, I used an M-Audio Revolution 7.1 for recording. Analog output ports were used on all systems. To keep things simple, I’ve translated RightMark’s word-based quality scale to numbers. Higher scores reflect better audio quality, and the scale tops out at 6, which corresponds to an “Excellent” rating in RightMark.

Despite its lack of hardware acceleration, the Envy24PT should shine in RightMark Audio Analyzer’s quality tests, but it’s not that simple. We tested the SN25P’s output through the front, rear, and Wolfson-powered outputs, and performance was mixed. With the exception of the stereo crosstalk test, the Wolfson DAC doesn’t appear to provide improved audio quality over the VT1617A codec.

Not content to let RMAA evaluate audio quality alone, I donned a pair of headphones and ran the SN25P through a series of back-to-back listening tests with uncompressed WAV audio files. To my ears, the Wolfson DAC’s output is a little richer and more detailed than that of the VT1617A. The two are remarkably close, but the Wolfson DAC presents subtle background sounds with slightly more clarity.

While I had the headphones out, I also tested for audio interference while performing disk-intensive tasks. The front headphone output on Shuttle’s Pentium 4-based P-series XPCs is particularly prone to interference during hard drive defrags, but as far as I can tell, no such issue plagues the SN25P. No amount of window-dragging, disk access, or other mischief could reproduce the SB95P’s noticeable hum.

ATA performance
ATA performance was tested with a Maxtor 740X-6L ATA/133 hard drive using HD Tach 3.01’s 8MB zone setting.

Scores are pretty even when we look at ATA performance, but the SN25P is a little sluggish in the write speed test.

Serial ATA performance
Moving to Serial ATA, we tested performance with a Western Digital Raptor WD360GD SATA hard drive. Again, we used HD Tach 3.01’s 8MB zone test.

For the most part, the SN25P’s Serial ATA performance is spot on. As you can see, our 10K-RPM Western Digital Raptor WD360GD can’t even burst fast enough to saturate Serial ATA’s 150MB/sec of available bandwidth. Serial ATA II who?

USB performance
Our USB transfer speed tests were conducted with a USB 2.0/Firewire external hard drive enclosure connected to a 7200RPM Maxtor 740X-6L hard drive. We tested with HD Tach 3.01’s 8MB zone setting.

Despite sharing the same nForce4 USB controller as the DFI and Foxconn motherboards, the SN25P manages quicker USB transfer rates.

Firewire performance
Our Firewire transfer speed tests were conducted with the same external enclosure and hard drive as our USB transfer speed tests.

The XPC’s Firewire performance doesn’t distance the system from the rest of the pack.

Ethernet performance
We evaluated Ethernet performance using the NTttcp tool from Microsoft’s Windows DDK. The docs say this program “provides the customer with a multi-threaded, asynchronous performance benchmark for measuring achievable data transfer rate”.

We used the following command line options on the server machine:

ntttcps -m 4,0,192.168.1.25 -a

..and the same basic thing on each of our test systems acting as clients:

ntttcpr -m 4,0,192.168.1.25 -a

Our server was a Windows XP Pro system based on Chaintech’s Zenith 9CJS motherboard with a Pentium 4 2.4GHz (800MHz front-side bus, Hyper-Threading enabled) and CSA-attached Gigabit Ethernet. A crossover CAT6 cable was used to connect the server to each system.

The nForce4 boards were tested with the NVIDIA Firewall and Jumbo Frames disabled.

Despite the nForce4’s lack of ActiveArmor hardware acceleration for Gigabit Ethernet, the SN25P manages higher throughput than the nForce4 Ultra’s GigE controller.

Update 6/13/2005 — We recently discovered that the ntttcp CPU utilization results included in this review were incorrect. The CPU utilization results have been removed, but they didn’t factor prominently into our overall conclusion, so that remains unchanged. A full explanation can be found here.

Overclocking
For our overclocking tests, we swapped our low-latency OCZ PC3200 memory out of the SN25P in favor of some of the OCZ’s PC4400 sticks, which are rated for higher clock speeds at more relaxed latencies. PC4400 memory is designed to operate at speeds of up to 550MHz, so it shouldn’t bottleneck our overclocking efforts. However, running the PC4400 memory at more relaxed 2.5-3-3-8 timings could result in lower overall performance if we can’t crank the clock speed high enough to compensate.

In testing, we were able to get the SN25P stable with a 230MHz HyperTransport link and a 10x CPU multiplier that kept the processor reasonably close to its default 2.2GHz clock speed. Unfortunately, we had to drop the HT link multiplier down to 3x to get the system stable with a 230MHz HyperTransport link. The system would boot with a 4x HT multiplier, but only up to HyperTransport link speeds of 225MHz.

I’ve presented scores for the overclocked SN25P at both 10x225MHz with a 4x HT multiplier and 10x230MHz with a 3x HT multiplier.

With a 230MHz HT link speed, a 3x multiplier clocks the HyperTransport processor link at only 690MHz—much slower than our 10x225MHz configuration, whose HT link is running at 900MHz. However, neither Unreal Tournament 2004 nor Sphinx seem to mind the slower HT link speed. Both tests prefer the 10x230MHz configuration’s slightly higher memory bus and processor clock speed.

Noise levels
We measured noise levels 1″ from the SN25P’s front, side, and rear using an Extech Model 407727 Digital Sound Level Meter. Measurements were taken after 10 minutes at idle, and then after another 10 minutes of a Folding@home CPU load. We also measured noise levels with Shuttle’s XPC SB95P V2 and SB86i for comparison. Those systems were equipped with a Pentium 4 520 2.8GHz processor and Radeon X600 XT graphics card, but otherwise had similar hardware to our SN25P. The SN25P and SB95P V2 used their default Smart Fan setting, but the SB86i requires its Mid fan speed setting to maintain stability under load.

With an Athlon 64 3500+, our SN25P system is much quieter than either Pentium 4 520-equipped XPC. That isn’t a particularly surprising result. However, notice that the SN25P barely gets louder under load, and that’s not even with Cool’n’Quiet enabled.

Conclusions
It looks like the XPC SN25P was worth the wait, but it will take a BIOS update for the system to realize its full potential. At the very least, Shuttle needs to implement more aggressive memory timings, including a 1T command rate. While they’re at it, a PCI clock lock and 0.5x CPU multipliers should also be added to give overclocking enthusiasts a little more flexibility. Finally, it would be nice if the smart fan’s temperature trigger were exposed, either through a BIOS update or an official XPC Tools release that works with the SN25P.

All those issues could, ideally, be resolved with a quick BIOS or software update. Hopefully that update will come, and sooner rather than later, because the rest of the system borders on sublime. The more time we spend with the P-series chassis, the more we love its spacious interior, tool-free design, and robust 350W power supply. The SN25P’s three cooling zones might be overkill for an Athlon 64, but with temperature-controlled fans, the system doesn’t make any more noise than it needs to.

Oh, and don’t forget that there’s an nForce4-based motherboard lurking under the hood with PCI Express, Gigabit Ethernet, plenty of Serial ATA RAID, and Envy24PT audio. The vanilla nForce4 may lack a couple of the Ultra’s features, but few users will miss them. In a PCI-less small form factor system like the SN25P, I’d rather have an nForce4/Envy24PT combo than an Ultra, anyway.

Shuttle XPC SN25P February 2005

In the end, the SN25P is a BIOS update away from being the ultimate enthusiast-oriented small form factor system. The XPC’s $420 suggested retail price isn’t cheap, but it’s the first Athlon 64-based small form factor system with PCI Express support, and it could be worth every penny.