Seek time has improved only 5-10 times since the 1970s.
This is an embarrassment in the computer industry!
RAID - a way to improve disk performance, along with availability.
This is a set of parallel disks, managed by one controller which makes
it a “virtual one disk” for the operating system (a big selling point!).
Data are spread over different disks of RAID, which allows parallel
access. This is how speed (throughput) is improved.
Disks may also contain redundant information (e.g., every disk has
a “twin” holding its copy). This is how availability is improved.