Zero-copy

"Zero-copy" describes computer operations in which the CPU does not perform the task of copying data from one memory area to another or in which unnecessary data copies are avoided. This is frequently used to save CPU cycles and memory bandwidth in many time consuming tasks, such as when transmitting a at high speed over a network, etc., thus improving the performance of programs (processes) executed by a computer. Zero-copy programming techniques can be used when exchanging data within a user space process (i.e. between two or more threads, etc.) and/or between two or more processes (see also producer–consumer problem) and/or when data has to be accessed / copied / moved inside kernel space or between a user space process and kernel space portions of operating systems (OS). Usually when a user space process has to execute system operations like reading or writing data from/to a device (i.e. a disk, a NIC, etc.) through their high level software interfaces or like moving data from one device to another, etc., it has to perform one or more system calls that are then executed in kernel space by the operating system. If data has to be copied or moved from source to destination and both are located inside kernel space (i.e. two files, a file and a network card, etc.) then unnecessary data copies, from kernel space to user space and from user space to kernel space, can be avoided by using special (zero-copy) system calls, usually available in most recent versions of popular operating systems. Zero-copy versions of operating system elements, such as device drivers, s, network protocol stacks, etc., greatly increase the performance of certain application programs (that become processes when executed) and more efficiently utilize system resources. Performance is enhanced by allowing the CPU to move on to other tasks while data copies / processing proceed in parallel in another part of the machine. Also, zero-copy operations reduce the number of time-consuming context switches between user space and kernel space.