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Why do CPUs 'tick'?

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Thread replies: 21
Thread images: 1

Why do CPUs 'tick'?
>>
>>51509357
Because they have a clock.
>>
>>51509380
Can they not have a clock?
>>
>>51509437
Then how would you overclock?
>>
>>51509357
Because clockboy solders them.
>>
Is it because 1 tick = 1 operation?
>>
>>51509437
https://en.wikipedia.org/wiki/Asynchronous_circuit
>>
>>51509900
>A CPU
>without a clock
>doubled area for completion detection
Not gonna happen
>>
>>51509380
But CPU's are older than mohammed
>>
>>51509871
>1 tick
>1 operation.
not really...
first of all the data path of a processor is pipelined into different stages, which means it takes several clock cycles to complete the processing of one command, but at the same time it starts to process one command and finishes one command.

second: this pipeline is stalled if a resource conflict occurs.

third of all todays processors are CISC processors which means commands from the assembler in your executable gets split up into smaller ones before processing them.

and last but not least. if you have a multi core processor it does all of this multiple times.
>>
>>51509457
This
>>
>>51510344
I still don't understand why it needs a clock. Why can't it just proc an operation and let it run through the circuit without a clock?
>>
>ask why cpus grind noise/tick
>"it's the fan"
It's not the fan, cellphones don't have fans.
If I'm in a quiet room and put my phone at my ear, I hear my phone making the CPU "grinding" noise, a whine, and ticks, it's really faint but it's there
>>
>>51510467
Because then the circuits would technically run at infinite speed only limited by latency.

As side from physical reasons why this would be terrible, think about a marching band, now think of a marching band with everyone doing there own thing at their own pace.
>>
>>51510590
This guy gets it, digital logic curcuits usually operate on the positive edge of a square wave, thus all the components do one move at a time, imagine a game of chess where each turn only one piece move, now imagine that same game of chess without any notion of taking turns, thus we need clocks. (There are non clocked circuits but they are unpredictable and hard to program) The clock is merely a crystal that resonates at a certain frequenc when given current. I work at Nvidia's hardware design and VSLI lab, our GPU's are worse than AMD's but we get higher pay ;)
>>
>>51510467
Basically because a circuit doesn't know if and when all signals are propagated. (if you use a result too early it is wrong.)

That's where the clock helps. the clock is set to a delay where every signal in the circuit has enough time to propagate, so it
(kinda) ensures that results of calculations are valid and ready to use in the next step e.g. saving the result into a register.

The type of circuit
>>51509900
described adds a logic network to each signal which is specifically engineered to propagate slower than the signal it's assigned to, to see if that signal has propagated.

but that method
1. uses more than 2x as much chip area for the same circuit,
2. which leads to more heat, more energy used, etc. etc.
3. needs extra work for every single signal/bus
(and believe me there are enough busses and signals in a processor to lose the overview. )
>>
>>51510570
>phone with a microdrive
the fuck?
>>
>>51509357
because GPUs tock :^)
>>
>>51510590
So if we removed the clock we would have infinitely fast processors... brb im gonna give AMD a call!
>>
Okay you faggots let me tell you how over-clocks work.

First of all, the original clock is just a quartz crystal. However, the quartz only operates at 100MHz. We use digital circuits in order to multiply the rate of the clock signal by "shifting" the square wave, monitoring and keeping the waves in phase.

Next, instead of taking the Von Neumann computing model to heart, we actually try to work with programs out of sequence, guessing which branches will be taken while each instruction is carried out. We also do value guessing in order to do some of the guess work.
>>
>>51510467
You can design such a circuit, but it's more complicated. The catch is it needs to also deliver a hazard-free 'completion' signal in some form or another in addition to the answer.
In grad skool, the lab next to mine specialized in asynchronous processors.
Thread posts: 21
Thread images: 1


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