Go: What is the difference between buffered and unbuffered channels?

Unbuffered — synchronous. Buffered — asynchronous up to capacity.

Unbuffered channel:

• No capacity.
• Blocks on send until receive.
• Synchronous communication.

1ch := make(chan int)
2
3go func() {
4    ch <- 1  // Blocks until received
5}()
6
7value := <-ch  // Unblocks sender

Buffered channel:

• Has capacity.
• Blocks only when full.
• Asynchronous up to capacity.

1ch := make(chan int, 3)
2
3ch <- 1  // Doesn't block (buffer not full)
4ch <- 2  // Doesn't block
5ch <- 3  // Doesn't block
6ch <- 4  // Blocks until space available

When to use:

• Unbuffered — synchronization, handoff.
• Buffered — rate limiting, batching.