Your OS does the equivalent of ob_start() on packet network sockets by default. See SO_SNDBUF, TCP_CORK, and TCP_NODELAY option to setsockopt(). If data sent o

Your OS does the equivalent of ob_start() on packet network sockets by default. See SO_SNDBUF, TCP_CORK, and TCP_NODELAY option to setsockopt(). If data sent over packet network wasn't bufferend, most of the time partial frames would be sent. With buffering, the OS usually sends full frames, making better use of bandwidth, at slight expense of delay and tiny extra memory use. There is even some tunable smarts built-in to keep delay down to manageable size. The OS tries to create full frames from partial writes from applications. If OS didn't provide that service, it would be up to application to align write size for optimal bandwidth utilization. You don't really want PHP developers to have to think about size of strings they output, now do you? ;-) For reference, http://www.pbm.com/~lindahl/mel.html http://www.pbm.com/~lindahl/mel.html -- a guy that hand-picked intervals between instructions in drum memory for better performance -- not exactly the kind of work for typical webdeveloper.