Multiple choiceQuestion 1 · Recall
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By the end you can explain what the system clock does, relate clock speed to a clock cycle time, and say what the Immediate Access Store (IAS) is for.
Every part of a computer has to act at exactly the right moment — otherwise data would arrive while the receiving register was still busy.
The system clock is a small quartz crystal that vibrates when electricity passes through it, producing a steady stream of electrical pulses. Each rising pulse is a clock cycle: one beat in time for the whole machine.
The clock's signal is broadcast to the CPU and the buses, so every component steps through its work on the same beat. The Control Unit uses those beats to time its control signals.
Clock speed
The number of clock cycles per second, measured in hertz (Hz) — 1 Hz means one cycle per second. Computers use MHz ( Hz) and GHz ( Hz).
Worked example: From gigahertz to nanoseconds
A processor runs at Hz. How long does one clock cycle take?
Main memory is large but comparatively slow to reach. The CPU often needs the same few values over and over.
The Immediate Access Store is a small, very fast store inside the processor that keeps the data and instructions currently being used, so the CPU can reach them without going out to main memory each time.
It is far smaller than main memory — it holds the current working set, not the whole program.