RLL (Run Length Limited)
An encoding scheme used during write operations to facilitate data readback.
ROM (Read Only Memory)
Integrated circuit memory chip containing programs and data that the computer or host can read but cannot modify. The computer can read instructions out of ROM, but cannot store data in ROM.
RPM (Revolutions per Minute)
Rotational speed of the media (disk), also known as the spindle speed. Hard drives typically spin at one constant speed. The slower the RPM, the higher the mechanical latencies. Disk RPM is a critical component of hard drive performance because it directly impacts the rotational latency.
The straight-line path from the center of the disk to the outer edge of the disk.
Random Access Memory (RAM)
Memory that allows any storage location to be accessed randomly, as opposed to tape drives, which are sequential access devices.
Performs the data encoding and conversions the drive needs to write computer generated information onto a magnetic medium and then read that information back with a high degree of accuracy.
A data accuracy check performed by having the disk read data to the controller, which in turn checks for errors but does not pass the data on to the system.
A read error that the drive can correct by ECC recovery or by re-reading the data.
Redundant Arrays of Independent Disks (RAID)
Groupings of hard drives in a single system to provide greater performance and data integrity.
The amount of delay in obtaining information from a disk due to the rotation of the disk. For a disk rotating at 5200 RPM, the average rotational latency is 5.8 milliseconds. See also Mechanical Latency.