Power-Up In Standby (PUIS) Feature
Power-Up in Standby is a hard disk drive feature that allows drives to be powered up into a different power management state that will actually minimize current at power-up and allows the host to sequence the spin-up of the device. This means that when power is applied to the hard drive with PUIS enabled, the drive will not automatically spin up as expected. The purpose of this feature is to help save energy and it helps avoid a power consumption peak that can occur when multiple disks are powered at the same time. The spin up will only occur after the ATA command is issued to spin up the drive.
One of the most common times that computer technicians may run into a hard drive in PUIS mode is if they were to pull a hard drive from a set top box. Set top boxes such as your cable boxes sometimes set the internal hard drives to enable PUIS. The set top box makes the decision when to allow the drive to enter another power management state. This feature enabled in drives has caused much head scratching when techs have pulled supposedly working hard drives from set top boxes and plugged them into their computer to find out that the drive is not working.
Another good usage for PUIS being enabled is when a system supports multiple hard disk drives such as in a RAID. Depending on the RAID setup, maybe not all disks are needed immediately in a system. By allowing the BIOS to determine when to allow spin up of the drive, current spikes are avoided within the system creating a safer environment for the electronics involved.
Power-Up in Standby is a great energy saving solution for smaller devices or for energy-efficient devices. However, since we now have SSD’s (or solid state drives), these can also resolve the power issue of spinning disk drives. Maybe once prices go way down in the future, we will start seeing SSD’s even in our set top boxes!