⚡ Latency Numbers Every Programmer Should Know

Understanding the relative speed of different operations in computing is crucial for writing efficient code. Below is a list of key latency numbers, from CPU cache accesses to network round trips.

🏎️ CPU & Memory Operations

Operation	Time	Emoji Representation
🏷️ L1 cache reference	0.5 ns	🔥 Ultra-fast
🔀 Branch mispredict	5 ns	🔄 Slight penalty
🏷️ L2 cache reference	7 ns	🚀 Fast
🔐 Mutex lock/unlock	100 ns	🔒 Synchronization cost
🎯 L3 cache reference	30 ns	🎯 Moderate speed
🧠 Main memory reference	100 ns	📦 Memory access

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📡 Data Compression & Transfer

Operation	Time	Emoji Representation
📦 Compress 1K bytes with Zippy	10 µs	🗜️ Compression cost
🌐 Send 2K bytes over 1 Gbps network	20 µs	📡 Network transfer
📚 Read 1 MB sequentially from memory	250 µs	📖 RAM read

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🏢 Datacenter & Disk Operations

Operation	Time	Emoji Representation
🏢 Round trip within the same datacenter	500 µs	🔄 Local network
💽 Disk seek (random access on HDD)	10 ms	🛑 Expensive
🌍 Read 1 MB sequentially from the network	10 ms	🌐 Internet speed
💾 Read 1 MB sequentially from SSD	1 ms	⚡ Fast storage
📀 Read 1 MB sequentially from HDD	30 ms	🐢 Slow disk access

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🌎 Network & Intercontinental Transfers

Operation	Time	Emoji Representation
🚀 Packet transmission across the US	50 ms	✈️ Coast-to-coast
🌍 Packet round-trip US → Europe	100 ms	🌐 Intercontinental
🚀 Packet round-trip CA → Netherlands → CA	150 ms	🛰️ Global transfer
🚀 Packet one-way Earth → Mars (at closest distance)	4-24 min	🛸 Interplanetary delay

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🔥 Key Takeaways

• Nanoseconds (ns) ⚡: CPU operations, cache, and memory references.
• Microseconds (µs) ⏳: Network and data compression operations.
• Milliseconds (ms) 🐢: Disk access, network round trips.
• Minutes 🚀: Deep-space communication delays.

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