Clock Cache Visualizer: The Second Chance Algorithm

Animate the Clock (Second Chance) cache replacement used in real operating systems. Watch the clock hand sweep and reference bits flip.

Clock (Second Chance): how it works

What is Clock?
Clock is an O(1) approximation of LRU using a circular buffer. Each frame has a reference bit (R). A clock hand sweeps around, clearing bits until it finds a victim.
The Algorithm
On a miss, advance the hand. If R=1, clear it (give a second chance) and keep moving. If R=0, evict this frame, insert new page, set R=1, advance hand.
Why it's used in OS
Clock is used in real OS page-replacement (Linux, macOS) because it approximates LRU with O(1) operations and avoids maintaining a strict access order.

Animate the Clock (Second Chance) cache replacement used in real operating systems. Watch the clock hand sweep and reference bits flip.

What is Clock?
Clock is an O(1) approximation of LRU using a circular buffer. Each frame has a reference bit (R). A clock hand sweeps around, clearing bits until it finds a victim.
The Algorithm
On a miss, advance the hand. If R=1, clear it (give a second chance) and keep moving. If R=0, evict this frame, insert new page, set R=1, advance hand.
Why it's used in OS
Clock is used in real OS page-replacement (Linux, macOS) because it approximates LRU with O(1) operations and avoids maintaining a strict access order.