of power management which uses a number of specific power modes that save energy by reducing performance. When implemented an HDD will change between a full power mode to one or more power saving modes as a function of drive usage. Recovery from the deepest mode, typically called Sleep, may take as long as several seconds. Shock resistance Shock resistance is especially important for mobile devices. 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. Maximum shock tolerance to date is 350 g for operating and 1,000 g for non-operating. SMR drives Hard drives that use shingled magnetic recording (SMR) differ significantly in write performance characteristics from conventional (CMR) drives. In particular, sustained random writes are significantly slower on SMR drives. As SMR technology causes a degradation on write performance, some new HDD with Hybrid SMR technology (making it possible to adjust the ratio of SMR part and CMR part dynamically) may have various characteristics under different SMR/CMR ratios. Comparison to solid-state drives Solid-state devices (SSDs) do not have moving parts. Most attributes related to the movement of mechanical components are not applicable in measuring their performance, but they are affected by some electrically based elements that causes a measurable access delay. Measurement of seek time is only testing electronic circuits preparing a particular location on the memory in the storage device. Typical SSDs will have a seek time between 0.08 and 0.16 ms. Flash memory-based SSDs do not need defragmentation. However, because file systems write pages of data that are smaller (2K, 4K, 8K, or 16K) than the blocks of data managed by the SSD (from 256KB to 4MB, hence 128 to 256 pages per block), over time, an SSD's write performance can degrade as the drive becomes full of pages which are partial or no longer needed by the file system. This can be ameliorated by a TRIM command from the system or internal garbage collection. Flash memory wears out over time as it is repeatedly written to; the writes required by defragmentation wear the drive for no speed advantage. See also vRPM Hybrid drive IOPS Standard RAID levels References Computer storage devices Hard disk drives Computer peripherals