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Lenovo ThinkCentre M91p Ultra-small Desktop PC

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The USFF version of Lenovo’s ThinkCentre M91p packs a significant punch in a small package. Utilizing an Intel “S” low power processor and a 150W external AC power adapter, it’s also incredibly energy efficient.

Lenovo ThinkCentre M91p Ultra-small Desktop PC

April 4, 2012 by Lawrence Lee

Product Lenovo ThinkCentre M91p Ultra-small Desktop PC
Manufacturer Lenovo
MSRP US$799 (base model)
US$939 (sample configuration)

Through the years Lenovo (formerly IBM) has developed a reputation for rock solid personal computer systems. Their ThinkPad line is particularly famous for its Spartan qualities that appealed to both business and home users alike. For the white collar masses who find themselves chained to desks and cubicles for much of the day, there is the ThinkCentre series, with the M91p being the current flagship model. To suit specific needs it actually comes in three different forms, a traditional bulky microATX tower, a slimmer low profile case, and an even tinier ultra-small form factor enclosure.


The ultra-small form factor ThinkCentre M91p box.


The machine itself.

If the USFF version of the M91p looks familiar, it’s probably because they’ve recycled the case from last generation’s model, the M90p (the even older M58p also had a similar chassis). Like most PCs built for commercial use, it has a boxy no-nonsense shape with a matte black finish, giving off the impression that absolutely no fun is on the agenda. While its appearance is mind-numbingly dull compared to the many sleek home computers marketed to regular consumers, its dimensions are appealing to all. It takes up less than one square foot of space when placed horizontally and is only about three inches thick.

The hardware inside is also impressive, not compromising on performance despite the diminutive size. Not only does the USFF M91p utilize Sandy Bridge processors, they belong to Intel’s "S" line, low power quad core chips with a TDP of just 65W. As the M90p used dual core Clarkdale CPUs, the M91p is more powerful but doesn’t increase the energy footprint. Energy efficiency is a big selling point for corporate PCs as even a small power savings can be significant if there are a high number of systems in operation. The motherboard is also based on the Q67 chipset which supports advanced security and management features like Intel’s vPro and AMT (Active Management Technology) as it’s important to be able to lock things down on a business PC.


AC power adapter, keyboard, and mouse.

As the M91p is equipped with a 65W processor and lacks discrete graphics, the provided external 150W AC adapter is sufficient to run the entire system. Small desktops are typically powered by internal FlexATX units which aren’t as efficient, generate noise, and take up valuable space inside the chassis. Like most proper pre-built PCs, the machine ships with a simple mouse and keyboard. There’s an internal speaker as well so all you need to get it running is a display.

Lenovo ThinkCentre M91p Ultra-small Desktop: Specifications (from the product
web page
)
Processor Intel Core i5-2500S (2.7GHz, 6M Cache)
Operating System Genuine Windows 7 Professional 64
Mechanical Package Eco USFF 1×2, Intel Q67, (WW except Russia)
Memory 4GB PC3-10600 1333MHz SODIMM (1 DIMM)
Graphics Integrated Intel Q67
Storage 500GB, 7200 RPM SATA
Optical Drive DVD Recordable (with DVD Playback & Burner Software) for Win 7
Networking Integrated Gigabit Ethernet Intel Q67
Warranty On-site 1 Year Part / 1 Year Labor
Note: Component upgrades over the base configuration in bold.

The base model of the M91p has an i5-2400S processor, 2GB of RAM, and a 250GB hard drive, so our sample’s configuration is a substantial upgraded. The i5-2500S in particular is a big step up, capable of hitting 3.7 GHz with Turbo Boost (the i5-2400S can only reach 3.3 GHz). It’s also a highly coveted chip that is not available in retail channels. Noticeably absent from the specifications are features like eSATA and USB 3.0, surprising as the latter is standard on most Sandy Bridge boards.

PHYSICAL DETAILS

The Lenovo ThinkCentre M91p’s shell is the same as the M90p, measuring 27.5 x 23.8 x 7.9 cm or 10.8 x 9.4 x 3.1 inches (L x W x H) and weighing 4.2 kg (9.2 lb). As the case is fairly compact there is room for only a single optical drive and hard disk, and one low profile PCI expansion card.


Exposed at the front of the case is a standard size DVD burner, a pair of USB 2.0 ports, mic and line-out jacks, and a large concave power button. There are small rubber feet on the bottom and side so the M91p can stand vertically to save floor/desk space.


There are two intake vents with the larger one being home to a built-in speaker. The sound quality is a little tinny and it crackles at high volume levels, but overall it’s an adequate substitute for cheap desktop speakers. It’s also superior to most laptop/tablet speakers we’ve encountered.


Rear ports: AC power, DisplayPort, VGA, 6 x USB 2.0, RJ45 (Intel gigabit ethernet), audio.


Powering the system is a bulky 150W, 19.5V AC adapter with a class V efficiency rating (87% between 49W and 250W).


The keyboard included has a standard layout with soft, springy keys.


The optical mouse has a generic, inoffensive symmetrical shape suitable for both lefties and righties.

INTERIOR

An important aspect to consider when choosing an office PC is how convenient the machine is to service. The M90p was just about perfect in this regard, so we have little issue with the M91p recycling its design. It cleverly opens up like a clamshell without using any tools and because it’s a small case, the components are immediately accessible. You don’t have to grope your way through the interior of a big tower to disconnect cables, etc.


Opening up the M91p is just about the easiest thing in the world. Just release the plastic latch at the back to unlock the hinge.


The bottom half of the case is home to a motherboard with two DDR3 SO-DIMM slots, two SATA ports (one 6 Gbps, one 3 Gbps), and a low-profile PCI riser slot. An aluminum heatsink is bolted atop the CPU with a plastic duct connecting it to an exhaust fan at the back.


The system’s only fan is an AVC 60 mm ball bearing unit, model number DS06025B12U. It’s quite powerful with a rotational speed of 5200 RPM and a power rating of 0.70A (8.4W). The use of fan isolators seems to be ironic.


The DVD burner and hard drive are mounted on the top half of the case so the hard drive is located just above the CPU heatsink when the enclosure is closed.


The hard drive, a Seagate 7200.12 500GB is padded with rubber grommets.


The caddy is secured to the interior by a shallow plastic tab on each side. It’s a loose arrangement, a tempting invitation for hard drive vibration. This is the only physical issue we have with the chassis.

TEST METHODOLOGY

Software and Measurement/Analysis Tools:


Device listing.

Testing Procedures

If available, the latest motherboard BIOS is installed prior to testing. Certain services/features
like Indexing, Superfetch, System Restore, and Windows Defender are disabled
to prevent them from causing spikes in CPU/HDD usage. We also make note if energy
saving features like Cool’n’Quiet/SpeedStep or S3 suspend-to-RAM do not function
properly.

Our test is a simple one, determine the overall AC power consumption, noise level, and heat output and
at various states. To stress the CPU, we
use either Prime95 (large FFTs setting) or CPUBurn depending on which produces
higher system power consumption. To stress the IGP, we use FurMark, an OpenGL
benchmarking and stability testing utility.

Test Results

System Measurements
System State
Temps
Power (AC)
dBA @1m
dBA @0.6m†
CPU
HDD
Ext*
Off
N/A
2W
N/A
Sleep (S3)
N/A
4W
N/A
Idle
34°C
32°C
27°C
22W
20
24
H.264 Playback
35°C
32°C
26°C
29W
20
24
CPU Load
69°C
33°C
30°C
78W
24
28
CPU + GPU Load
78°C
34°C
32°C
92W
24
28
Ambient: 22°C, 10~11 dBA.
*External temperature measured using an IR thermometer pointed at the hottest portion of the chassis.
We measure SPL at 0.6m for all devices meant to be used atop a desk, as it is more realistic a distance than the usual 1m. It also corresponds to the "seated user SPL" distance specified in the computer noise measurement standard ISO 7779.

Both the Core i5-2500S processor and the included 150W AC power adapter are very energy efficient. The M91p to consumed an impressive 22W when idle and 92W on full load, far less than a desktop using a traditional internal power supply. The hard drive, despite being positioned just above the CPU heatsink stayed under 35°C throughout testing and the case didn’t heat up much either. CPU temperatures were not great on load, but that was to be expected given the system’s tight confines.

We were concerned that noise would be an issue, but the system wasn’t terrible loud considering the performance of the CPU and the form factor of the case. The machine generated 20 dBA@1m (24 dBA@0.6m) at idle and during H.264 video playback, and 24 dBA@1m (28 dBA@0.6m) on load. The BIOS lacks customizable fan control options and no tool we tried could monitor the fan speed, but the exhaust fan seemed to ramp up very gradually as the system heated up.



The Lenovo ThinkCentre M91p measured 24 dBA@0.6m and 28 dBA@0.6m when idle and on load respectively.

While the overall noise level was decent, the quality of the noise left much to be desired. At 0.6m inside our anechoic chamber we could detect an audible rattle and buzzing coming from the fan’s motor. Small, high speed, ball bearing fans aren’t typically smooth sounding, but it wasn’t solely responsible for the noise being generated. The system produced a noticeable hum caused by hard drive vibration passed onto the case; We could feel the exterior shaking slightly. The CPU/VRM circuitry also generated some coil whine, a high-pitched squeal that presented at idle only, disappearing once any type of CPU load was introduced. This too was audible at 0.6m but dissipated with distance.

Comparison vs. M90p

System Measurements
System State
USFF ThinkCentre M91p (Core i5-2500S)
USFF ThinkCentre M90p (Core i5-650)
CPU Temp
dBA @0.6m
Power (AC)
CPU Temp
dBA @0.6m
Power (AC)
Idle
34°C
24
22W
23°C
24
40W
H.264 Playback
35°C
24
29W
32°C
26
56W
CPU Load
69°C
28
78W
78°C
30~31
95W
CPU + GPU Load
78°C
28
92W
85°C
30~31
115W
Ambient: 22°C, 10~11 dBA.
*External temperature measured using an IR thermometer pointed at the hottest portion of the chassis.
We measure SPL at 0.6m for all devices meant to be used atop a desk, as it is more realistic a distance than the usual 1m. It also corresponds to the "seated user SPL" distance specified in the computer noise measurement standard ISO 7779.

Compared to last USFF ThinkCentre sent to us by Lenovo, the M90p featuring the same case, the M91p is an environmentally superior machine. It runs cooler and quieter on load and uses substantially less energy thanks to the i5-2500S. The power consumption numbers are staggering, almost half that of the M90p when idle, and a 20% improvement on load. The CPU also has two more cores, so it’s significantly more powerful to boot.

CPU/GPU Performance

The i5-2500S is a rather rare CPU for sale to OEMs only and is not available through retail channels. It’s a 65W quad core Sandy Bridge chip with a 2.7 GHz clock speed that can be Turbo Boosted up to 3.7 GHz. Thus in single-threaded applications its performance is comparable to the i5-2500K, while multithreaded performance is closer to that of the i5-2400S (2.5 GHz, 3.3 GHz with Turbo Boost). It is equipped with the same integrated HD 3000 graphics processor as the 2500K. For performance analyses of these chips, please read our reviews listed below:

Hard Drive Performance


HD Tune Read benchmark result.

Though the Seagate 7200.12 line is a bit long in the tooth, the 500GB model had a respectable file transfer rate according to HD Tune. The 18.1 ms access time was very poor though, similar to what you would find on a "green" drive.

Pre-installed Software

Aside from the typical Windows bloatware like Adobe Reader, Bing Bar, Microsoft Silverlight, a trial edition of Office 2010, and a Norton Internet Security installer, the M91p came with Corel Burn.Now, Corel DVD MovieFactory, and a host of Lenovo system management utilities.


HD Tune Read benchmark result.

The ThinkVantage Toolbox is the star of this menagerie, tying everything together into a portal to a variety of system settings, diagnostics and miscellaneous information. What they’ve done is essentially pulled settings and menus native to Windows and put it all in one easy to find location and dressed it up. While we would like to say it adds something extra for the experienced PC user, it seems more of a tool for the neophyte rather than the IT professional performing maintenance or troubleshooting a problem.

Audio Recordings

These recordings were made with a high resolution, lab quality, digital recording
system inside SPCR’s own 11 dBA ambient anechoic chamber, then converted to
LAME 128kbps encoded MP3s. We’ve listened long and hard to ensure there is no
audible degradation from the original WAV files to these MP3s. They represent
a quick snapshot of what we heard during the review.

Each recording starts with ambient noise, then 10 second segments of product
at various states. For the most realistic results,
set the volume so that the starting ambient level is just barely audible, then
don’t change the volume setting again while comparing all the sound files.

FINAL THOUGHTS

The Lenovo ThinkCentre M91p hits most of the relevant marks for an enterprise-class desktop PC. The Q67 chipset gives it advanced security and management features and the Core i5 "S" processor delivers high speed, quad core performance with truly impressive energy efficiency. The power savings over the Clarkdale-powered M90p with the same case were substantial. Though based on relatively recent hardware, the system does lack quite a few extraneous features like USB 3.0 and eSATA. It’s a powerful PC, but in many regards it’s rather basic.

Expansion is severely limited due to the form factor, so if you require a system with more versatility, the M91p also is available in two larger sizes depending on your needs. The USFF case is not new, being used previously with the M90p, but this is a good thing. It’s compact, takes little space on the floor or desk and perhaps most importantly, is incredibly easy to open. This last quality is simply magnificent making it extremely convenient to perform physical maintenance and upgrades. It’s the type of thing we wish was more common in consumer PC cases. Our only complaint about the design is how loosely the hard drive is secured.

While these types of systems aren’t typically designed for low noise operation, the M91p is reasonable in this department as the office/corporate environment generally has more ambient background noise than at home. We would recommend keeping it at a distance of one meter or greater or keeping under a desk though. The quality of the noise generated is worse than the total volume, especially at close proximity. The hard drive mount makes the entire case vibrate, the fan’s ball bearing motor has an unpleasant rattle, and the CPU/VRM circuitry emits coil whine when idle. The M91p is squarely pegged as a business PC, unsuitable for home use due to these noise issues and presence of premium chipset features that would likely go unused in non-corporate settings.

Custom Alternative to Lenovo ThinkCentre M91p
(Base Configuration, US$799)
Component
Model
Street Price*
Processor
Intel Core i5-2400S
$200
Motherboard
Intel BOXDQ67EPB3
$120
Memory
Crucial Rendition 2GB DDR3-1333
$10
Hard Drive
WD Caviar Blue 250GB
$50
Optical Drive
Samsung SN-208BB Slim DVD Burner
$25
Case/PSU
Antec ISK 300-150
$75
Keyboard/Mouse
Microsoft Wired Desktop 400
$15
Speakers
Cyber Acoustics CA-2012
$10
Operating System
Windows 7 Professional 64-bit OEM
$140
 
TOTAL
$645
*Rounded to the nearest US$5.

A common way to gauge the value of a pre-built machine is to see how its price stands up to that of a comparable custom system. We priced an equivalent DIY build to the M91p’s base configuration and found it to be cheaper by US$154. While this seems large, it’s actually fairly reasonable compared to most business PCs on the market. It’s also difficult to put a dollar value on the M91p’s slimmer, easy to open enclosure, and far superior warranty and support.

Our thanks to Lenovo
for the ThinkCentre M91p Ultra-small Desktop PC sample.

* * *

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