Question

what is the main storage medium for computers which is made up of a collection of disk

Answer 1

internal hard drive for primary storage
optical disks,flash drives,external hard drive for secondary storage

Answer 2

The main storage medium for computers which is made up of a collection of round magnetic disks is called a Hard Disk Drive (HDD).

Although it is used as a primary storage device, Hard Disk Drives should not be confused as the primary memory of the computer system. The primary memory of a computer system is its Random Access Memory (RAM) module which has a tremendous Random Access speed to which even a Solid State Drive (SSD) is of no match.

So, the HDD (Hard Disk Drive) is used as the main storage medium but as secondary memory in a computer system.