Main memory – only large storage media that the CPU can access directly.
Secondary storage – extension of main memory that provides large nonvolatile storage capacity.
Magnetic disks – rigid metal or glass platters covered with magnetic recording material .
Disk surface is logically divided into tracks, which are subdivided into sectors.
The disk controller determines the logical interaction between the device and the computer.
Moving-Head Disk Mechanism
Storage systems organized in hierarchy.
Caching – copying information into faster storage system;
main memory can be viewed as a last cache for secondary storage.
Use of high-speed memory to hold recently-accessed data.
Requires a cache management policy.
Caching introduces another level in storage hierarchy.
This requires data that is simultaneously stored in more than one level to be consistent.
Migration of A From Disk to Register