Seagate Momentus 5400.2 120GB SATA notebook drive

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August 9, 2005 by Devon Cooke with Mike Chin


Seagate Momentus 5400.2 ST9120821AS
120GB, 5,400 RPM Notebook drive



Market Price

As a general rule, notebook drives tend to be significantly quieter than their larger desktop cousins. Yes, they are a little slower and smaller, and they cost more per gigabyte, but in terms of noise they are second to none. The light acoustic signature makes notebook drives desirable for the quietest desktop systems. It's a discovery made by many SPCR readers.

Seagate is dominant among HDD makers, owning at least half of the global hard drive business. It created the first truly low noise 7200 RPM desktop drive in the Barracuda IV some four years ago. The B-IV was in another class for noise compared to other drives of its day, and it remains one of our reference quiet drives. Since then, Seagate's position in HDD noise has been eroded, with no clear low-noise leaders among either desktop or notebook drives. Seagate introduced the Momentus notebook drives a year and a half ago, along with a commitment to make 2.5" the top enterprise HDD form factor within a couple of years. This process is one we continue to watch.

Seagate's entire notebook line is sold under the Momentus name, and includes countless models of varying spindle speed, capacity, and interface. What identifies a product are the numbers after the name. Our sample is a 5400.2, indicating that it is a second generation 5,400 RPM Momentus. SPCR reviewed one of the original 5,400 RPM Momentus drives when we asked Is the Silent Future 2.5" Wide? over a year ago, and we were disappointed to find that it produced a pure high pitched tone that was louder than our reference desktop drives. However, several users in our forums have noted that newer drives do not exhibit this sound, so we returned to the Momentus line with high hopes.

This Momentus 5400.2 sample has plenty to set it apart from its competitors. It is one of the few SATA notebook drives on the market currently, only the second SATA notebook drive we're examining, and its 120 GB capacity is a step above the competition. Even so, Seagate has recently announced a third generation: The 5400.3 features Full Disc Encryption as an added security measure against data theft. However, at the time of writing, none of these have appeared in retail channels.

The Momentus 5400.2 120GB model.

SEAGATE MOMENTUS 5400.2 ST9120821AS (quoted from Seagate's web site)

SoftSonic FDB motor: Delivers inaudible operating acoustics

Inaudible is a bold claim, but not impossible for a notebook drive. Just remember that "inaudible" is relative to ambient noise.

QuietStep ramp load technology: Enables whisper-quiet load/unload acoustics and 900 G's of non-operating shock tolerance

Loading and unloading the heads often sounds like ordinary seek noise.
Operating shock of 250 Gs to withstand rugged notebook environment According to Seagate: "An operating shock of 225 Gs is equivalent to dropping a typical notebook computer approximately three inches flat onto a concrete surface while it is running."

8-Mbyte cache buffer: Optimizes performance so applications run fast and smooth

8 MB is standard for notebook drives these days.

5400-RPM spin speed: Provides almost 50 percent more performance for notebook computers while maintaining battery longevity

The 50% figure is in relation to 4,200 RPM drives, which are starting to be discontinued.
Serial ATA with Native Command Queuing: Blazing fast 1.5Gb/s interface speed combined with NCQ for high performance SATA is very convenient, especially for desktop users: No adapter is required to connect it to a modern motherboard.


The specifications below are specific to model that we examined. Capacity, cache size, platter number, interface, and even performance vary from model to model even within a single product line. Acoustics and power dissipation also vary depending on the number of platters in the drive; smaller capacity drives tend to have fewer platters, and tend to produce less noise and use less power.

Specifications: Seagate Momentus 5400.2 ST9120821AS
120 GB
8 MB
Spindle Rotation Speed
5,400 RPM
SATA 1.5 Gb/s
5.6 ms
Average Seek
12.5 ms
Internal Transfer Rate
336 Mbits / second
0.1 kg
Operating Temperature
5 - 55°C
Power Dissipation: Idle / Seek
0.8 / 2.2 W
Acoustics (Idle)
2.4 Bels

The SATA interface has not yet become common for the notebook form factor. Most notebooks use a version of the EIDE interface, and this is reflected in the marketplace availability of SATA notebook drives. SATA is quite desirable as many desktop motherboards ship with only a single IDE channel. Furthermore, SATA notebook drives do not require an additional adapter to work properly in a desktop system.

It must be noted that SATA is set to sweep notebook drives, and all the brands will soon be avaible in SATA; it's just a question of time. Notebook PC makers will adopt SATA as their exisiting supplies (and contracts for supplies) of components related to the previous IDE/ATA connector are depleted. These include not only the drives, but also notebook motherboards with native plug in ports for drives, and any other peripherals that may go into a notebook HDD interface.

Another step forward is the increased capacity. Although 120 GB is hardly large in desktop terms, it is 20 GB larger than almost every other notebook drive on the market. The one exception, as far as we know, is the 120 GB Fujitsu MHV2120AT, which is a slower 4200 RPM drive. Every other 2.5" mobile drive appears to be limited to 100 GB. Most users will probably stick to the lower capacity models anyway, as the extra 20GB capacity isn't enough to justify buying it for archival or A/V purposes. On the other hand, the extra 20 GB may be useful to a user (like me) who chronically runs out of space no matter how much storage there is.

Even if the extra capacity isn't needed, it still has the ancillary benefit of a small performance boost thanks to increased areal density. This benefit should apply to the models that use 60 GB platters: The 120 GB, 60 GB, and 30 GB models. The other capacity models in the 5400.2 line may not benefit, but it's impossible to say for certain without knowing how Seagate has manufactured them ¬ó or by performance benchmarking the drive.

Keep in mind that this performance advantage over smaller drives is theoretical. We do not have enough experience with the performance of current notebook drives to say for certain how much the higher areal density benefits performance, nor are we interested in doing serious performance benchmarking.

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