For example, getting the system time involves an IPC call to the user-space server maintaining system clock. The caller first traps into the kernel, causing a context switch and memory mapping. The kernel then checks that the caller has required access rights and that the message is valid. If it is, there is another context switch and memory mapping to complete the call into the user-space server. The process must then be repeated to return the results, adding up to a total of four context switches and memory mappings, plus two message verifications. This overhead rapidly compounds with more complex services, where there are often code paths passing through many servers.