Various storage devices used by an operating system can be arranged as follows in increasing order of accessing speed :

1. AMagnetic tapes → magnetic disks → optical disks → electronic disks → main memory → cache → registers
2. BMagnetic tapes → magnetic disks → electronic disks → optical disks → main memory → cache → registers
3. CMagnetic tapes → electronic disks → magnetic disks → optical disks → main memory → cache → registers
4. DMagnetic tapes → optical disks → magnetic disks → electronic disks → main memory → cache → registers