Computer Storage Systems

Study Notes

Storage is a way to keep information long-term, replacing traditional methods like paper storage.

A storage device is used in computers to store data, providing one of the core functions to modern computers.
Storage devices can be classified based on accessibility by the computer and the methods through which they save their data.

Primary storage: also known as main memory, connected directly or indirectly to CPU through memory bus, includes RAM, ROM, and Cache.
Secondary storage: not directly accessible by CPU, accessed through input/output channels, includes hard disk.
Tertiary storage: a comprehensive computer storage system that is usually very slow, used to archive data that is not accessed frequently, involves a robotic mechanism.
Offline storage: also known as disconnected storage, not under the control of a processing unit, must be inserted or connected by a human operator, includes floppy disk, USB flash drive, and memory card.

A hard disk is the main and usually largest data storage device in a computer.
Hard disk capacities range from 160 GB to 2 TB.
Hard disk speed is measured in revolutions per minute (RPM), ranging from 4500 to 7200 RPM.
Disk access time is measured in milliseconds.

Paper storage: has pros like no need for electricity or internet, confidential information can be easily locked away, but has cons like difficulty in making backups, hard to convert or reuse, and takes up lots of space.
Optical storage: uses different reflections of light to read data, and a laser to write data, examples include CDs, DVDs, and Blu-Ray, has pros like reliability, good portability, and easy to pack and carry, but has cons like slower read/write speed, need a disc drive to use, and smaller capacity per unit.
Magnetic storage: examples include hard disk drives (HDD), cassettes, and swipe cards, data is written by changing magnetism on the disk/tape and read by detecting this, has pros like large capacities, cheap to buy, and usually reliable, but has cons like generally not durable, slower read/write times, and failures can occur.
Solid State Drives: have no moving parts, electronic circuits are used to store the data, examples include SSDs and flash memory devices like USB memory sticks and memory cards, has pros like generally reliable, durable, portable, and faster read/write times, but has cons like higher cost per GB, sometimes limited number of writes, and reliability problems long-term.