What are the differences between HTTP/1, HTTP/1.1, and HTTP/2?

HTTP/1.0

• Each request requires a new TCP connection, closed immediately after completion (short-lived connections)
• Cannot reuse connections, resulting in poor performance

HTTP/1.1

• Persistent Connections (Keep-Alive): TCP connections are kept alive by default and can be reused
• Pipelining: Multiple requests can be sent at once, but responses must be returned in order (Head-of-Line Blocking problem)
• Added Host header, supporting virtual hosting
• Supports Chunked Transfer Encoding

HTTP/2

• Multiplexing: Multiple requests/responses handled in parallel over a single TCP connection, solving HOL Blocking
• Header Compression (HPACK): Compresses repeated headers to reduce data transfer
• Server Push: Server can proactively push resources to the client without waiting for a request
• Binary Framing: Data transmitted in binary format for higher efficiency
• Still based on TCP; TCP-level packet loss can still cause HOL Blocking

Summary Comparison

Feature	HTTP/1.0	HTTP/1.1	HTTP/2
Connection	New each time	Persistent	Persistent
Multiplexing	Not supported	Not supported (Pipelining)	Supported
Header Compression	None	None	HPACK
Server Push	None	None	Supported
Transfer Format	Text	Text	Binary