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A block, a contiguous number of bytes, is the minimum unit of storage that is read from and written to a disk by a disk driver.The earliest disk drives had fixed block sizes (e.g. the IBM 350 disk storage unit (of the late 1950s) block size was 100 six-bit characters) but starting with the 1301 [8] IBM marketed subsystems that featured variable block sizes: a particular track could have blocks ...
When using Advanced Format drives with legacy operating systems, it is important to realign the disk drive using software provided by the hard disk manufacturer. Disk realignment is necessary to avoid a performance degrading condition known as cluster straddling where a shifted partition causes filesystem clusters to span partial physical disk ...
The specification was released on December 20, 2011, as a mechanism for providing PCI Express connections to SSDs for the enterprise market. Goals included being usable in existing 2.5" and 3.5" form factors, to be hot swappable and to allow legacy SAS and SATA drives to be mixed using the same connector family. [2]
Enhanced Small Disk Interface (ESDI) was an attempt to minimize controller design time by supporting multiple data rates with a standard data encoding scheme; this was usually negotiated automatically by the disk drive and controller; most of the time, however, 15 or 20 megabit ESDI disk drives were not downward compatible (i.e. a 15 or 20 ...
The disk drives would measure the disk's "health parameters", and the values would be transferred to the operating system and user-space monitoring software. Each disk drive vendor was free to decide which parameters were to be included for monitoring, and what their thresholds should be. The unification was at the protocol level with the host.
Hard disk drives use a rotating magnetic disk to store data; access time is longer than for semiconductor memory, but the cost per stored data bit is very low, and they provide random access to any location on the disk. Formerly, removable disk packs were common, allowing storage capacity to be expanded.
A USB flash drive connects via USB and is not constrained by shape and size as a card is. [2] [11] In general, an SSD uses a relatively fast interface such as Serial ATA (SATA) or PCI Express (PCIe) paired with a logical device interface such as AHCI or NVM Express (NVMe).
Non-volatile random-access memory (NVRAM) is random-access memory that retains data without applied power. This is in contrast to dynamic random-access memory (DRAM) and static random-access memory (SRAM), which both maintain data only for as long as power is applied, or forms of sequential-access memory such as magnetic tape, which cannot be randomly accessed but which retains data ...