S.M.A.R.T. - a technology that allows to monitor a device state and in some cases predict a failure based on the observed data.
Most modern devices support S.M.A.R.T. technology.
48-bit address (LBA48) - a technology that allows a device to handle 48-bit sector addresses.
Using the technology it is possible to produce IDE/ATA/ATAPI disks larger than 137.4 GB. All modern disks support LBA48.
Host Protected Area (HPA) - a hidden area on a hard disk which is invisible and inaccessible to an operating system.
Hardware vendors may use HPA to store a copy of OS installation which is used to restore system in case of failure.
Device Configuration Overlay (DCO) - a disk capability to hide a part of disk space from an operating system, BIOS, and user, similar to HPA.
It is used to set exactly the same size for different hard disks, useful in RAIDs.
When HPA and DCO are used simultaneously, disk size limitation set by DCO takes precedence.
Automatic Acoustic Management (AAM) - a disk capability to reduce the noise produced by a disk during its work at the expense of the disk performance.
AAM works by reducing speed of head movements. This affects access time, but not linear read speed.
Advanced Power Management (APM) - inidcates device support for power-saving functions, like a hard drive spinning down when it is not in use.
Power-up in standby (PUIS) or power management 2 mode (PM2) - a capability of a SATA or PATA disk not to spin up automatically when power is on.
Spinning up only takes place only when a disk is accessed.
PUIS allows a RAID controller to spin the disks up in turn rather than all at once to decrease peak load on a power supply.
Power consumption at start-up is high; therefore, it is better to spin up the disks one by one rather than all at once.
This is sometimes called staggered start or staggered spin-up.
Native Command Queuing (NCQ) - a capability of a SATA disk to reorder requested read/write operations to improve performance.
Tagged Queuing (TCQ) - very similar to NCQ but used for SCSI and some ATA/100 disks. Also note that algorithms of reordering requests in TCQ and NCQ are slightly
Free Fall Control (FFC) - a capability of a hard drive to determine that it is falling down and to park the head away from the platter.
Typically used in the laptop disks to decrease the probability of disk damage and data loss in case a laptop falls.
Trusted Computing - indicates that a storage device supports a set of commands to facilitate secure and tamperproof data transfer and storage.
TRIM - a special command which allows an operating system to tell a device that certain data blocks are not used anymore and therefore can be erased.
This applies only to solid state drives (SSD) and allows to speed up the subsequent writes.