Hard disk drive performance characteristics
It is composed of a few independently measurable elements that are added together to get a single value when evaluating the performance of a storage device.
The cost and power per usable byte of storage rises as the maximum track range is reduced.
[18][19] Measured in dBA, audible noise is significant for certain applications, such as DVRs, digital audio recording and quiet computers.
For example, Seagate offers a set of features in some drives called Sound Barrier Technology that include some user or system controlled noise and vibration reduction capability.
[22] It depends on the rotational speed of a disk (or spindle motor), measured in revolutions per minute (RPM).
The spindle motor speed can use one of two types of disk rotation methods: 1) constant linear velocity (CLV), used mainly in optical storage, varies the rotational speed of the optical disc depending upon the position of the head, and 2) constant angular velocity (CAV), used in HDDs, standard FDDs, a few optical disc systems, and vinyl audio records, spins the media at one constant speed regardless of where the head is positioned.
Power consumption has become increasingly important, not only in mobile devices such as laptops but also in server and desktop markets.
Increasing data center machine density has led to problems delivering sufficient power to devices (especially for spin-up), and getting rid of the waste heat subsequently produced, as well as environmental and electrical cost concerns (see green computing).
Recovery from the deepest mode, typically called Sleep where the drive is stopped or spun down, may take as long as several seconds to be fully operational thereby increasing the resulting latency.
A current widely used standard for the "buffer-to-computer" interface is 3.0 Gbit/s SATA, which can send about 300 megabyte/s (10-bit encoding) from the buffer to the computer, and thus is still comfortably ahead of today's disk-to-buffer transfer rates.
Defragmentation is a procedure used to minimize delay in retrieving data by moving related items to physically proximate areas on the disk.
Although automatic defragmentation is intended to reduce access delays, the procedure can slow response when performed while the computer is in use.
Because heat and vibration limit rotational speed, increasing density has become the main method to improve sequential transfer rates.
Simply increasing the number of tracks on a disk can affect seek times but not gross transfer rates.
Without interleaving, the next logical sector would arrive at the read/write head before the equipment was ready, requiring the system to wait for another complete disk revolution before reading could be performed.
However, because interleaving introduces intentional physical delays between blocks of data thereby lowering the data rate, setting the interleave to a ratio higher than required causes unnecessary delays for equipment that has the performance needed to read sectors more quickly.
Modern technology is capable of reading data as fast as it can be obtained from the spinning platters, so interleaving is no longer used.
Power consumption has become increasingly important, not only in mobile devices such as laptops but also in server and desktop markets.
Increasing data center machine density has led to problems delivering sufficient power to devices (especially for spin up), and getting rid of the waste heat subsequently produced, as well as environmental and electrical cost concerns (see green computing).
Some laptops now include active hard drive protection that parks the disk heads if the machine is dropped, hopefully before impact, to offer the greatest possible chance of survival in such an event.
[49] Measurement of seek time is only testing electronic circuits preparing a particular location on the memory in the storage device.
