Hi, I assumed that stream wrote data directly to it's associated device, but after a few tests I found I was wrong. I wrote this code snippet: <--- Code ---> int main() { using namespace std; using namespace boost::iostreams; string src; src.assign(10 * 1024, 'a'); size_t size = src.size(); // ContainerDevice is from boost::iostreams::example typedef ContainerDevice<std::vector<char> > MyDevice; vector<char> container; string str; container.reserve(size); str.reserve(size); for (size_t i = 0; i < 1000000; ++i) { // Version 1 MyDevice device(container); stream<MyDevice> io(device); io.write(src.c_str(), src.size()); io.flush(); container.clear(); // Version 2 #if 0 str.insert(str.end(), src.begin(), src.end()); container.insert(container.end(), str.begin(), str.end()); str.clear(); container.clear(); #endif } return 0; } <--- Code-End ---> The first version(write data to the device by stream) is slower than the second(copy data, then copy again to device), so I guess stream do some unnecessary copy operations (eg: copy data to inner buffer, then copy again from buffer to device). I tried replacing stream<MyDevice> io(device); with stream<MyDevice> io(device, 0, 0); to set inner buffer size to 0, but the result was much more slower. I set a breakpoint at ContainerDevice::write(const char_type* data, std::streamsize n) then found n passed was always 1, which means every call wrote only 1 byte. If there is a way to write data directly to the device, my program will be very efficient. thanks.