2.5 Inch Form Factor Factors
When we think of 2.5 inch form factor HDDs, we think of our notebook. This dates back to early notebooks that used 2.5 inch FF drives with a Parallel ATA (PATA) interface. In the above image you can see that the PATA power and data connector was spread out across the entire drive in both directions. The SATA power and data connectors took up roughly half the space of PATA and have allowed HDD manufacturers to get creative with the height of their drives.
Traditional platter drives still dominate all spectrums of the market and the taller a drive is, the more platters it can have. Technologies like perpendicular recording have allowed more data to be stored on each platter, something we refer to as areal density. The racing world has a saying that holds true for hard drives as well; There is No Replacement for Displacement. It is easier to add more platters to a drive than it is to miniaturize the size of the data on the platters. To achieve this, hard drive makers needed to make 2.5 inch drives larger.
When we reviewed the Intel X25-M, we made a note about just how thin the drive actually was. In the above image you can see the 7mm X25-M compared to a standard notebook 9mm drive. This was the first time I had ever seen a 7mm drive and at the time didn't give it much thought. Last month Seagate held a private briefing for the press that outlined their plans for a new 7mm line up of products.
The Seagate Momentus Thin Laptop Hard Drive is designed for a new category of notebooks. This new category of portable products rests between the ultra small size netbooks and the notebooks that we currently use today. The goal is to be able to bridge the price gap between the two categories that we have now. The Momentus is a single platter design that will cost less than 9mm products that normally use dual platters.
Here we see a traditional 9mm drive compared to a Seagate 12mm 15K.2. The 9mm drive market will remain the "standard" for the 2.5 inch form factor for many years to come. These drives allow for more platters than the 7mm drives, but are still small enough to work in a majority of products.
9mm is sort of like the Jack of All Trades when it comes to portable devices. They can operate at 5,400 or 7,200 RPMs and are able to hold up to 500GB of data at this time. Even more attractive is the current price of 9mm drives. You can walk into any Best Buy in the country and spend less than 100 USD for a Western Digital Scorpio Black with 320GB on 7,200 RPM platters. With prices like those, you really have to wonder just how low the price of single platter 7mm drives are going to go.
12.5mm and 15mm
The largest two versions of the 2.5 inch form factor started out as enterprise products. The 12.5 and 15mm heights allow for capacity sizes of up to 1TB or spindle speeds of up to 15,000 RPMs. Most of the larger 2.5 inch FF drives were sold with a SAS interface, but that is starting to change.
When Hitachi released their first SATA 2.5 inch FF drive with 500GB of capacity, the first of its kind, it was in a 12.5mm package and designed for consumers. The drive saw little success since very few notebooks were able to accept 12.5mm drives. The Sony Playstation 3 did work with the Hitachi 500GB drive and many PS3 enthusiasts jumped at the opportunity to increase their systems capacity.
We are now starting to see more consumer large height drives come from drive manufacturers. The most popular by far has been the Western Digital VelociRaptor. WD sold these drives in a 2.5 to 3.5 inch adapter, but that was the point when PC enthusiasts were introduced to this standard that was previously reserved for enterprise servers.