is a long time manufacturer in the storage market that I'm sure many of our readers are familiar with. Not only content with "making" drives, Seagate are also innovators in the field, constantly developing many unique and industry standard technologies. A recent contribution to the consumer drive market is obviously SATA, and more recently Native Command Queuing.

Over on the portable storage front, not as much press is given simply because most people are simply content with what they have. This field has changed though as more and more manufacturers are developing notebooks that can do much more than just write reports and crunch numbers. Gaming especially, as well as multimedia have created a need for more diverse and powerful hardware, including the humble notebook hard drive.

We've covered their fast (7200 RPM) and big (120GB) Seagate Momentus models here at Viper Lair in the past, and today we'll be looking at the Momentus 5400.3 Hard Drive which promises not only to be fast, but comes armed with a staggering 160GB of storage capacity. Seagate has done more than jamming a bunch of platters though as they are also the first to ship drives based on a new technology dubbed Perpendicular Recording.

Seagate Momentus 5400.3 160GB

On the surface, the Momentus 5400.3 looks like any other 2.5" notebook drive. Our particular model is an Ultra ATA model, hence the familiar IDE pin layout. Naturally, since power is drawn through the IDE interface, it's not an out of the box solution for desktop PCs, but completely suitable for notebooks and notebook drive based hardware. A SATA version will be forthcoming, but the ETA is unknown at this point.

The Momentus 5400.3 will carry several different model numbers depending on the capacity (currently, choices are 40GB, 60GB, 80GB, 120GB and the 160GB we're reviewing). The 160GB model carries a model number of ST9160821A. Compared to the Momentus 5400.2, no changes have been made to the seek times (12.5ms), and cache sizes (8MB). Here is a cheat sheet comparing the 5400.3 to the 5400.2:

	5400.3	5400.2
Speed (RPM)	5400	5400
Areal density	132 Gbpsi	110 Gbpsi
Discs/Heads	2/4	2/4
Recording Technology	Perpendicular	Longitudinal
Shock tolerance	350g	250g

Compared to the Momentus 5400.2, the Momentus 5400.3 makes the following improvements; greater capacity, better shock tolerance (350G's over 250G's), fewer platters, and less heat. The increase in areal density allows Seagate to use fewer platters compared to their previous Momentus and as a result less power will be used and reliability will be improved. This allows for 4200rpm-like power performance and with everything else in a notebook getting more powerful, anything that takes a load off the batteries will be appreciated. Keep in mind that these comparisons are if "all capacities being equal". The chart above shows that both drives use 2 discs, 4 heads, but the 5400.2 requires this for 40GB less capacity.

Since many users are road warriors, the Momentus 5400.3 makes a big jump in shock tolerance. The 5400.2 has a tolerance of 250G's, and some robust competitors are in the 300 range. The 5400.3 ups the anté to 350g's. A drive does not have to be turned on to take damage from a fall, and Seagate has boosted the nonoperating tolerance to 900G's.

All this is nice and dandy, but a lot of what Seagate has set out to accomplish with the Momentus would not be possible without the next topic of discussion...

Perpendicular Recording

Before heading into the numbers part of the review, we think it's a good idea to go over perpendicular recording. This is probably a new technology to most of you, as it was certainly new to most of us here at VL. We received a briefing back in December 2005 prior to the hard launch earlier last month, and needless to say, there is a lot of information to absorb.

The easiest way to create bigger hard drives is to increase the areal density. Seagate's desktop 400GB drives for example use 133GB platters, and therefore require fewer platters than they would if the areal densities were lower. For notebook drives, the Momentus 5400.2 120GB drive hovers at about 110 Gigabits/square inch, but the Momentus 5400.3 160GB drive bumps it up to 132 Gigabits/square inch. A byproduct usually when increasing the areal density is performance normally gets a small boost since the drive head does not have to move as much.

In layman's terms, here's a simple example. Imagine you have a 4 foot long open box with candy bars in there (Chocolate = Good). If you lie them down flat lengthwise along the box, you can maybe fit 12 bars (3 bars per foot). Because they are lying lengthwise; i.e., bigger bits, using one hand, you can maybe grab 1 bar per second. That's our food example of longitudinal recording.

For perpendicular recording, take the same box, but stack the candy bars standing up. Since they are placed in the box this way, you can fit more bars; i.e. smaller bits, higher areal density. This method will allow you to grab more bars. Therefore the higher candy bar density enables you to not only have more bars, but also a faster candy grabbing rate, or in the case of perpendicular recording, a higher data rate.

Seagate has demonstrated a recording areal density with perpendicular recording of 245 Gigabits/square inch with a data rate of 480MBits/second, double that of the Momentus 5400.2. In theory, 500 Gigabits/square inch should be possible with perpendicular recording technology.

Conventional drives rely on longitudinal recording. What this means is that the bits are laid horizontally along the plane or surface of the disk. In theory, 250 Gigabits/square inch should be possible with longitudinal recording technology, but to do this, the data bits must continue to shrink and packed closer together. Eventually, as we hit the 250 Gigabits/square inch limit, the bits become to small and demagnetize.

Current longitudinal recording have a specific magnetic orientation as shown in the left image in the picture above. When these bits get smaller as explained earlier, they begin losing the ability to hold their magnetic orientations. As a result, the bit's magnetic north and south poles reverse without warning and corrupt data.

Perpendicular recording addresses the shortcomings of longitudinal recording by aligning the bit magnetization in a "standing" position. The soft underlayer illustrated above acts as part of the write field return path that produces an image of the recording head that effectively doubles the recording field.

Kudos to anyone who actually understood all of that, but here's an example forwarded to us from Seagate themselves:

"Magnetic recording is a lot like sewing. Think of the magnetic field from a write head as a needle, and the recording layer of a disc as the cloth you are trying to sew. The fabric is the magnetic strength of the disc (the coercively for techies) and the needle is the strength of the write head (the write field) Your data is the seam in the fabric. The more stitches per inch, the more data you store. To make your data durable, you want to use a thick fabric, and a long needle, but this gets in the way of making many stitches to the inch.

In longitudinal recording, the magnetic layer (the cloth) is laid directly onto the aluminum substrate. When data is written, it is like sewing with the cloth laid flat on a table. Going flat along the table, the needle can only make stitches far apart. If you use a shorter needle, and thinner cloth, the stitches get closer together, but the seam gets weaker and weaker. When the material gets too thin, the seam tears, and the data is lost.

In perpendicular recording, a soft underlayer is put down between the substrate and the recording layer. The soft underlayer lifts the cloth off the table, letting the needle go into the cloth straight up and down. Now you can put stitches very close together, and still use a long needle, and thick cloth. Your data seam has more stitches, and it is stronger as well."

In summary, perpendicular recording is the future and several companies outside of Seagate are going to be introducing drives based on this technology very soon. With that out of the way, let's look into the numbers.

NEXT