Hybrid disk drive:

Momentus XT incorporates traditional HDD with 500GB and SSD with 4 GB.

High speed due to the controller
Hybrid disk drive has a controller which places only “hot data” or data that is most directly associated with improved performance in the flash memory.

Recording
Controller records the data to the hard drive; direct recording to the SSD is prohibited.

Data distribution
Controller incorporated counter registers data access queries. The required data are copied to the flash memory.

Subsequent access
By repeated data reference, the controller transmits the query to the flash memory.

HDD
Storage device:
magnetic disks
Access: mechanical
(read/write head)
Advantages:
+ Relatively low price
+ Unlimited number of write operations
Disadvantages:
- Non-resistant to physical shock
- Low speed
- High power consumption
- Noise

SSD
Storage device:
semiconductor
Access: electronic
Advantages:
+ Resistant to physical shock
+ Low Power Consumption
+ Noiseless
Disadvantages:
- High price
- Limited number of write operations

High speed facilitated by the data control system

The main feature of hybrid disk drives is that the disk doesn’t let OS perform data distribution but it decides by itself which data should be placed in the flash memory. Such disk drives are compatible with all versions of Windows, Mac OS and Linux and they don’t require any driver installation. Besides, they look like HDDs. The controller decides which data is important for the user by recording all data references. Seagate named this technology Adaptive Memory. For example upon the first disk drive start, the controller places in the flash memory the data essential for OS loading. Upon the second start, to avoid slow data reading from the hard drive, the query is transmitted to the flash memory thus accelerating loading speed. This is facilitated by the fact that data reading from the Momentus XT flash memory goes 73% faster than from traditional HDD. With the lapse of time the user will witness considerable increase in performance since the controller counter records every started application files and places them in the flash memory. This process goes on until the flash memory is full. The controller doesn’t differentiate between various file types. It just remembers the blocks of data to which the user and OS refer and how often they do it.

On the one hand, SSD flash memory stores only essential data which contributes to the performance. On the other hand, data selection method implies that disk defragmentation causes data loss. Hybrid disk drive will run like a traditional HDD if upon the start of applications there is no enough space on the flash memory.

Traditional Recording Techniques

Recording technique of the HHDD is the same as that of the HDD since the controller uses the flash memory only to read data but all new data are recorded to the hard disk. The fact that Momentus XT can read data faster is conditioned by the spindle speed (7200 rpm) and 32 MB cache. New generation of hybrid disk drives has already proved its advantage over the 2.5” disk drives used in laptops. HHDD is also far better than the 3.5” disk drive used in the PC. However, efficiency of the HHDD is still subject to dispute. It cannot match a combination of the fast SSD which has enough disk space for OS and other software installation and the additional HDD for data storage. Thus it cannot compete with the SSD in the high-end PCs. However in middle-end PCs, replacement of the HDD with the HHDD, which is considerably faster, will prove advantageous.