wall time (real-world time or wall-clock time)

Wall time, also called real-world time or wall-clock time, refers to elapsed time as determined by a chronometer such as a wristwatch or wall clock. (The reference to a wall clock is how the term originally got its name.)

Wall time differs from time as measured by counting microprocessor clock pulses or cycles. The number of microprocessor clock cycle s per second of wall time depends on the microprocessor's clock speed . The microprocessor clock is not a chronometer, but a signal generator that outputs pulses at a high, precise, constant frequency . The microprocessor clock in a 2- Ghz computer ticks twice as fast (2,000,000,000 cycles per second) as the microprocessor clock in a 1-GHz computer (1,000,000,000 cycles per second). The so-called computer clock that displays chronological time in terms of the date, hour, minute, and second displays wall time, not the time in microprocessor cycles.

In practical computing, wall time is the actual time, usually measured in seconds, that a program takes to run or to execute its assigned tasks. When the computer is multitasking, the wall time for each program is determined separately, and depends on how the microprocessor allocates resources among the programs. For example, if a computer multitasks using three different programs for a continuous period of 60 seconds, one program might consume 10 seconds of wall time, the second program 20 seconds, and the third program 30 seconds. But these are not contiguous blocks; instead they are allocated in a rotating fashion, similar to time-division multiplexing in communications practice.

For a computer user, the total amount of elapsed time, as measured in days, hours, minutes, and seconds (denoted in the form dd+hh:mm:ss) that the computer has worked on a specific job is measured in wall time. This is not necessarily a single, contiguous block of time, because a computer may (and usually does) perform more than one job over a given period.