What is Latency

In computing,"latency" describes some type of delay. It typically refers to delays in transmitting or processing data, which can be caused by a wide variety of reasons.

Note: 1 ns = 1 * 10^-9 sec

In 1990:

• L1 cache reference: 181 ns
• L2 cache reference: 784 ns
• Branch mispredict: 603 ns
• Main memory reference: 207 ns
• Compress 1K bytes with Zippy: 362,000 ns
• Send 2K bytes over commodity network: 1448 ns
• Read 1 MB sequentially from memory: 3038000 ns
• Round trip within same datacenter: 500,000 ns
• Disk seek: 20,000,000 ns
• Read 1 MB sequentially from disk: 640,000,000 ns
• Read 1 MB sequentially from SSD: 50,000,000 ns

In 2000:

• L1 cache reference: 6 ns
• L2 cache reference: 25 ns
• Branch mispredict: 19 ns
• Mutex lock/unlock: 94 ns
• Main memory reference: 100 ns
• Compress 1K bytes with Zippy: 11,000 ns
• Send 2K bytes over commodity network: 45,000 ns
• Read 1 MB sequentially from memory: 301,000 ns
• Round trip within same datacenter: 500,000 ns
• Disk seek: 10,000,000 ns
• Read 1 MB sequentially from disk: 20,000,000 ns
• Read 1 MB sequentially from SSD: 5,000,000 ns

In 2010:

• L1 cache reference: 1 ns
• L2 cache reference: 4 ns
• Branch mispredict: 3 ns
• Mutex lock/unlock: 17 ns
• Main memory reference: 100 ns
• Compress 1K bytes with Zippy: 2000 ns
• Send 2K bytes over commodity network: 1000 ns
• Read 1 MB sequentially from memory: 30,000 ns
• Round trip within same datacenter: 500,000 ns
• Disk seek: 5,000,000 ns
• Read 1 MB sequentially from disk: 3,000,000 ns
• Read 1 MB sequentially from SSD: 494,000 ns

In 2020:

• L1 cache reference: 1 ns
• L2 cache reference: 4 ns
• Branch mispredict: 3 ns
• Mutex lock/unlock: 17 ns
• Main memory reference: 100 ns
• Compress 1K bytes with Zippy: 2000 ns
• Send 2K bytes over commodity network: 44 ns
• Read 1 MB sequentially from memory: 3000 ns
• Round trip within same datacenter: 500,000 ns
• Disk seek: 2,000,000 ns
• Read 1 MB sequentially from disk: 825,000 ns
• Read 1 MB sequentially from SSD: 49000 ns

Comparison of Cache Sizes