Clock Speed: Difference between revisions

Also, a processor cannot just move instantly from one clock cycle to the next. There is a lag between them, called latency. This is an issue with processors, but even more with RAM, which also has a clock speed. Latency means that there is a pause, when a component does nothing. It's the digital equivalent of inertia, and gets worse with poor hardware synchronization, because data has to sit and wait for components to open up for it. It's usually a microscopic fraction of a second, but with dynamic programs like video game graphics, latency cannot be ignored. High latency parts are either best left out of the system, or reserved for processing that doesn't involve graphics (physics, AI, and others).

Another issue with clock speed is in parallel operations. As an example, hard drives traditionally transferred data in parallel (16-bits at once). Later when performance improved, two problems started to come to play. The first was most obvious, the highest performance drives, SCSI drives, had up to 68 pins with huge connectors and thick cables. The second is a problem in which the margin for error that bits could arrive in shrinks with clock speed. Due to latency or other propagation delay, not all the bits arrive at once. When a clock signal is high, this is usually the "sampling" period where the other side checks to see if a bit arrived. At high speeds, this becomes very hard to maintain data integrity. This isn't really a problem though in mostly internal connections when noise and other delays are kept to a minimum.

There's a new type of CPU called ''clockless'' CPUs. Where in a clocked CPU the CPU's components use the clock's signal to synchronize their activity, in a clockless CPU the components talk to each other to coordinate and synchronize their activity. A clockless CPU is capable of greater speeds than a clocked CPU, since the clock speed of a clocked CPU is limited by the worst case scenario (the slowest possible response time of the slowest component), but CPUs rarely deal with the worst case scenario, and most components will get their work done before the next clock tick comes; the time the components spend sitting there waiting for the next clock tick is time they could have spent actually doing something if they were in a clockless CPU. On the other hand, a clockless CPU is a lot trickier to design than a clocked one, and the massive amounts already existing software which helps humans design CPUs are geared towards designing clocked CPUs.