Hybrid drive

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A hybrid drive is a new type of large-buffer computer hard disk drive. It is different from standard hard drives in that it employs a large buffer (up to 1 GB) of non-volatile flash memory to cache data during normal use. By primarily using this large buffer for non-volatile data storage, the platters of the hard drive are at rest almost all of the time, instead of constantly spinning as they are in current hard drives. This offers numerous benefits, chief among them decreased power consumption, improved reliability, and a faster boot process.

Hybrid drives are set to be released, primarily for notebook computers, in early 2007, with Samsung introducing their first drives in January, and Seagate in the first three months. At the moment, they are only known to be fully compatible with the upcoming Windows Vista operating system; Microsoft uses the name ReadyDrive to describe the software side of this technology.

The command interface will be standardized in the new revision 8 of the ATA standard.

1 Function explanation
2 Benefits
3 Drawbacks
4 See also
5 References
6 External links

[edit] Function explanation

Unlike most standard hard drives, the hybrid drive in its normal state has its platters at rest, as if it were off. During this time, any data that the user must write to the hard drive is written instead to the buffer. While working on a text document, for example, or browsing through the Internet, any temporary save files or the browser's cache will be saved to the buffer, instead of being written to the hard drive every time.

The hybrid drive's platters will spin up in only two situations. When the buffer begins to near its capacity, the platters of the hard drive will spin up, and all of the data in the buffer will be cleared onto the hard drive, whereupon the platters will again return to an off state, and the cache will be empty for use again. The second instance is when the user must access a new file from the hard drive that is not already stored in the buffer. In this case, the platters must spin up to access the file and place it onto the buffer, whereupon the platters will once again return to an off state.

Because the hybrid drive utilizes nonvolatile flash memory (such as those in a USB key), as opposed to volatile memory (such as RAM), the buffer is able to retain all the data even in the event of a sudden power failure or reboot, and can even store boot-up data into the buffer (see below).

Early estimates place the actual hard drive usage (when the platters are spinning) at anywhere between 1.25%^[1] and 10%^[2] for normal users, although there are obviously situations where the benefit will be smaller, such as the encoding or editing of very large video files. See flash memory for more disadvantages.

[edit] Benefits

The hybrid drives offer several benefits over the standard hard drive, especially for use in notebook computers.

Decreased Power Consumption: Because the platters will almost always be in an off state (as high as 98.75% of the time), power consumption by the hard drive will be drastically reduced. Although not so much of an issue for desktop computers, this greatly extends the battery life of notebook computers, where hard drives are one of the biggest energy consumers.

Decreased Heat Generation: The reduced spinning of the platters also greatly decreases the amount of heat generated, as few parts of the hard drive are physically moving (and generating friction). This is a benefit to all computers, in helping to keep the overall temperatures cooler, but especially notebooks, where space is tight and heat greatly affects maximum system performance, and overclocked computers, where the case temperatures play a significant role in how high the clock speeds of CPUs and graphics cards can be increased.

Decreased Noise Levels: In addition to the decrease in noise due to needing less overall cooling because of decreased power consumption and heat generation, hybrid drives are almost completely silent due the decreased use of the hard drive platters.

Improved Reliability: As the platters won't be spinning nearly as much, the wear and tear on the hard drive is drastically reduced. Hybrid drives should be able to last much longer than today's standard notebook drives. In addition to this, head crashes — in which a sudden movement, such as a violent impact, causes the read/write head of the hard drive to physically impact one of the platters, effectively killing the hard drive in most cases — will become much less frequent, as the head should be docked most of the time. ^{[citation needed]}

Faster Performance: Because the hybrid drive utilizes its flash memory buffer, rather than its platters, during normal use, accessing and writing to data should be significantly faster in most cases. The exception is when a new file must be accessed or the buffer nears its capacity, whereupon the platters must be accessed. In this case, the time needed for the platters to spin up might cause a delay. Conversely, because the platters are not constantly spinning, the decreased heat generation theoretically allows the maximum rotational speed of the hybrid drives to be augmented for short bursts beyond the current 15,000 rpm limit on SCSI drives or the 10,000 rpm limit on Western Digital Raptor drives, possibly allowing for an increased performance.

Instant Boot Process: By having such a large buffer (up to 1 GB), boot-up data for an entire operating system may be completely loaded into the hybrid drive's buffer. Reading from the buffer's flash memory instead of a hard drive's platters, computers using hybrid drives may be able to achieve extremely fast (under 10 seconds) or even near-instant boot up times.

[edit] Drawbacks

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There are also drawbacks to the use of hybrid drives:

Increased seek time: If the data being accessed is not in the cache and the drive has spun down, seek time will be greatly increased since the platters will need to spin up again.
Increased Cost: Flash memory chips are much more expensive per-gigabyte than comparably-sized traditional hard drives.
Flash memory has a limited number of write cycles before it fails, which is generally likely to be less than the number of write cycles for the same content when written to the actual platters of the disk. This means you are marrying a less reliable technology to the reliability of the HD resulting in the HD now becoming only as reliable as the Flash memory to which it is paired. In the event of failure of the flash memory it would be preferable if all the hard drive requirements are handled by the platters of the disk. This would prevent the user from losing the data already stored on the platters and avoid replacement of the drive.