MOESI Cache Coherence Protocol Simulator

Interactive demonstration of the MOESI (Modified-Owned-Exclusive-Shared-Invalid) cache coherence protocol. MOESI extends MSI by adding Owned (O) and Exclusive (E) states for better performance optimization.

Understanding the MOESI Protocol

MOESI Protocol States:

M (Modified): Cache line is modified, exclusive, and dirty
O (Owned): Cache line is owned by this cache, shared with others, responsible for memory updates
E (Exclusive): Cache line is exclusive, clean, and unmodified
S (Shared): Cache line is shared, clean, and read-only
I (Invalid): Cache line is invalid, not present in this cache

Key MOESI Advantages:

Owned state allows sharing dirty data without writing back to memory
Exclusive state enables silent transitions to Modified on writes
Reduced memory traffic through cache-to-cache transfers
Better performance for producer-consumer sharing patterns
Optimized writeback only when necessary

How to Use This Simulator:

Select a processor (P0 or P1)
Choose an operation (Read or Write)
Select a memory address (0x0 to 0x3)

For writes, enter a data value
Click "Execute Operation" to see the protocol in action
Observe state transitions highlighted in the table above

Try This Test Sequence:

P0 reads 0x0 → I→E (Exclusive access, no other copies)
P1 reads 0x0 → P0: E→S, P1: I→S (Both share clean copy)
P0 writes "100" to 0x0 → P0: S→M, P1: S→I (P0 gets exclusive write)
P1 reads 0x0 → P0: M→O, P1: I→S (P0 owns, P1 shares dirty data)

Simulation Controls

Processor

Operation Type

Memory Address

Data Value (for writes)

Processor Cache States

Processor 0 Cache

Cache Index	State	Data	Valid

Cache Performance: Hits: 0, Misses: 0

Processor 1 Cache

Cache Index	State	Data	Valid

Cache Performance: Hits: 0, Misses: 0

Bus Transaction Log & State Transitions

No operations performed yet. Execute an operation to see the transaction log.