Primary Storage – RAM, ROM & Secondary Storage

Primary Storage

• Consists of $RAM$ and $ROM$ located on the motherboard.
• Offers fast, direct access for the CPU.
• Split into volatile (needs power) and non-volatile (keeps data without power) memory.

$RAM$ (Random Access Memory)

• Volatile main memory; data lost when power is removed.
• Holds the operating system, active programs and data currently in use.
• Read/Write access; contents change constantly.
• Capacity affects multitasking and overall speed.

$ROM$ (Read Only Memory)

• Non-volatile firmware chip; retains data permanently.
• Stores the bootstrap program / $BIOS$ that starts the computer.
• Read-only under normal operation; rarely updated.
• Much smaller than $RAM$ but essential for startup.

Secondary Storage

• Non-volatile mass storage (e.g.
  • Hard Disk Drive
  • Solid State Drive)
• Holds OS, applications and user files when not in active use.
• Higher capacity, slower than $RAM$.
• Data persists after shutdown.

Tertiary Storage

• Removable/off-site backup media (tape, optical disk, cloud).
• Very high capacity, used for archiving and disaster recovery.

Power-On & Memory Use Sequence

1. Computer powers on; $BIOS$ in $ROM$ executes.
2. $BIOS$ finds the operating system on secondary storage.
3. OS kernel is copied into $RAM$ and starts running.
4. Opening an application: program code loaded from secondary storage into $RAM$.
5. Active files reside in $RAM$ until saved.
6. Clicking Save writes data back to secondary storage.
7. Powering off clears $RAM$; data remains only on non-volatile devices.

Quick Comparison

• Volatility: $RAM$ – volatile | $ROM$ & secondary – non-volatile.
• Capacity: secondary > $RAM$ > $ROM$.
• Access: $RAM$ – read/write | $ROM$ – read-only | secondary – read/write.
• Purpose: $ROM$ boots • $RAM$ works • secondary stores.

Three Storage Categories

• $Primary$: $RAM$, $ROM$.
• $Secondary$: HDD, SSD, USB, SD cards.
• $Tertiary$: Tape, optical jukebox, cloud backup.