Wartezyklen

Wartezyklen are additional processor clock cycles inserted into a memory or bus operation to wait for a slower peripheral or memory to respond. They arise when the time required by an external device to provide data or acknowledge a request exceeds the duration of a single CPU bus cycle. By extending the cycle with one or more wait states, the system remains synchronized and data integrity is maintained.

Mechanism and typical signals: In many classic microprocessors, the CPU monitors a ready or acknowledge signal from memory or I/O devices. If the device is not yet ready, the processor suspends progress and inserts one or more wait states. The exact number of wait states depends on how long the external device remains unready. Once the device asserts readiness, normal operation resumes. This mechanism is especially common in processors such as the 8086/8088 family, which used ready/wait handshakes to extend bus cycles.

Contexts where they occur: Wait states are most commonly associated with memory accesses and peripheral communication on systems with slower RAM, ROM, or I/O devices. They can also appear in simple or early computer architectures where memory speed and bus performance lag behind the CPU’s clock rate. In modern systems, explicit wait states are less visible to software because much of latency is hidden by caches and pipelining, but the underlying principle—stalling a stage of execution until data is available—remains relevant.

Impact and design considerations: While wait states enable reliable operation with slower components, they reduce effective memory bandwidth and overall performance. System designers mitigate them by using faster memory, adding caches, or reconfiguring interfaces to minimize wait times. In real-time and embedded contexts, predictable wait cycles can be important for meeting timing constraints.

See also: wait state, memory latency, bus cycle, ready signal.