SVID introduced record locking, which we have already examined. It also introduced and standardized some very important interprocess communication facilities, which are described as the IPC package . Compared with message passing, semaphores provide a rather low-level means of process synchronisation, not suited to the transmission of large amounts of information.
Semaphores are extremely efficient however, and are widely used.
Shared memory . This final IPC facility allows two or more processes to share data contained in specific memory segments. Shared memory represents an extremely efficient method of sharing data between processes, but relies of hardware support. Nearly all modern day computer systems provide the required level of hardware support. Although these facilities are part of UNIX SYSV, they are not an integral part of the kernel.