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March 01, ICT Lesson Notes

1. Secondary Storage

- Has connection between RAM and CPU
    - Secondary storage -> RAM -> CPU
- Used to store large amount of data (very large)

- Hard drive
    - How does it work?
        - Platters that stores data in 0/1
            - Platters only rotate one way, not both ways
        - Read/write head that looks like a little triangle
        - Access arm that holds the read-write head in place
        - The disk-like thing spins to allow platters to get read by read/write head
    - Usual speed: 
        - Typical: 5400 RPM (roll per minute)
        - Common in 2022: 7200 RPM
        - High-end: 10800 RPM
    - Since it's spinning always, performance will deteoriate by time
        - The more time you use, the slower it will become
        - Affects whole computer's performance
    - HDD is less durable / less shock resistant
    - Advantages
        - It's super cheap
        - Large storage space
    - Defragmentation
        - Rearranges blocks (of data) to make your HDD faster 
        - Moves platters of same file near to one another

- SSD (solid-state disk)
    - Two types
        - SATA (5x the speed of HDD)
        - M2 (almost 30x speed of HDD)
    - NO readwrite head NO motor
        - Performance does not deteoriate
        - More durable / more shock resistant
    - It's expensive
    - How does it work?
        - Send address to fetch data (similar like RAM)
        - Defragmentation also applies here but it only moves data blocks instead of platters