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38 votes
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What is a CPU clock physically?

Modern clocks are originally generated by quartz crystal oscillators of about 20MHz or so, and then the frequency is multiplied by one or more phase-locked loops to generate the clock signals for ...
Quitting Due To Antisemitism's user avatar
7 votes

What is a CPU clock physically?

A CPU clock is a signal which is used for two related purposes: Devices that are synchronous to a common clock agree that they will only look at signals from other such devices within a very short ...
supercat's user avatar
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7 votes

What are system clock and CPU clock; and what are their functions?

The answer provided by @Benjoyo is not accurate. The CPU clock can be lower than the system clock, at least in microcontrollers. As seen in this link, the PIC microcontrollers have the CPU clock, ...
bruno's user avatar
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6 votes
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Are vector clocks useful in centralized systems?

No, there's no need for a vector clock in a centralized system. A vector clock uses a $N$-vector of timestamps, where $N$ is the number of computers in the distributed system and the $i$th component ...
D.W.'s user avatar
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6 votes

What is a CPU clock physically?

This is a picture of a DIY quartz clock: This is (part of) a picture of a mainboard: Note the component I have marked with an arrow. You can see they look identical. Some caveats: Quartz crystals ...
AndreKR's user avatar
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5 votes
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Lamport logical clock: what does partial mean in the concept of `Partial ordering`?

The "partial ordering" in the papar means partial order as in standard mathemtics theory. To be more rigorous, the "partial ordering" in that paper, also called "irreflexive parital ordering" in that ...
John L.'s user avatar
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5 votes
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Why computer didn't use cesium atom to define 1 second?

First of all, the reason personal computers dont't use atomic clocks based on caesium is price. One CSAC (chip scale atomic clock) costs 5000 USD nowadays. The added precision is not worth the price ...
plshelp's user avatar
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4 votes
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How do computers synchronize their clocks with the standard time

The Network Time Protocol (NTP) uses a rather simple basis, it assumes that the roundtrip time is divided equally between up and down delays after server processing is subtracted. NTP keeps 4 ...
ratchet freak's user avatar
3 votes
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Lamport logical clock: why event occurs in a process with smaller pid is treated earlier?

No, "it doesn't make sense". You are correct in the sense that that choice is not a logical consequence of any requirements and known truths. It could be considered as arbitrarily selected. Well, we ...
John L.'s user avatar
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3 votes

Vector clock :why Singhal Kshemkalyani differential technique require FIFO for message passing?

All it's saying is that the messages between two processes need to be received in the order they are sent. If I'm going to send only differences between the previous message, we both better agree on ...
Derek Elkins left SE's user avatar
3 votes

Exactly how many clocks does a Computer consists of and how do they synchronize with each other?

So this is actually a very difficult question. It highly depends on the specific system used. So first we have to clarify some naming issues: Reading the book, I've came to understand that there are ...
GNA's user avatar
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3 votes

Exactly how many clocks does a Computer consists of and how do they synchronize with each other?

Modern processors tend to have more clocks than processors in the past, because that means when a part of the processor isn't used, it may be possible to switch off that part completely, including the ...
gnasher729's user avatar
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2 votes

How are lamport timestamps useful in practice?

As Wikipedia explains: The algorithm of Lamport timestamps is a simple algorithm used to determine the order of events in a distributed computer system. As different nodes or processes will typically ...
E. Douglas Jensen's user avatar
2 votes
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Whats the point of caching if the minimum single clock cycle time is the prorogation delay of the slowest component (fetching from DRAM)?

You are right that the clock speed is determined by the slowest stage. But on most architectures, it is not true that fetching (or any kind of memory access) takes one cycle. This is an illusion ...
Amaury Pouly's user avatar
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2 votes

Does two system's clock synchronises to communicate with each other?

Your question is a bit vague, depending on what is communicating, so I will try to give a general answer. There are essentially two big ways of communicating: Sending data together with a clock ...
Amaury Pouly's user avatar
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2 votes
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What happens when two different nodes have the same Lamport clock ID

tl;dr As Lamport writes at the top of page 561 of Time, Clocks, and the Ordering of Events in a Distributed System: To break ties, we use any arbitrary total ordering $\prec$ of the processes. To ...
Kai's user avatar
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2 votes
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Why is an accurate time so important for servers and computers?

It depends. If all atomic clocks would be turned off simultaneously, right now, that would be trouble. Because everyone relies on atomic clocks. And everything is organized in such a way that it doesn'...
gnasher729's user avatar
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2 votes

Resetting Vector clocks in distributed systems

Vector clocks overflow for the same reason that regular integers do. Vector clocks generally maintain a fixed number of bits per process to capture the event count for each respective process. There ...
Regan Koopmans's user avatar
1 vote

can UTC replace Lamport logical clocks?

In a distributed system, achieving perfect time synchronization among all nodes is often impossible. Lamport logical clocks are one way to deal with this problem. I presume that by "use UTC to ...
D.W.'s user avatar
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1 vote
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How can this MIPS processor execute one instruction in one cycle?

The register file in this design is multi-ported, and the read ports work like combinational circuits. The only thing between the read input and the output port is propagation delay. The clock signal ...
Pseudonym's user avatar
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1 vote

What is an example of an algorithm that requires synchronised clocks?

I did some more thinking about this and I see at least one benefit of synchronized clocks, which is 'fairness when the topology is skewed'. Imagine a situation with a server and two trusted clients. ...
MattCochrane's user avatar
1 vote

Metrics on which Clock Cycles Per Instruction(CPI) depends

In part a same processor is assumed, and 2 compilers are used. In part b, 2 processors with different clock frequency is used, ...
Shashank V M's user avatar
1 vote

Ordering of operations in a DAG of git commits

Assuming I understand the semantics: You cannot concurrently Create the same bug report twice, so that's not a problem Title could be a Last-Writer-Wins (LWW) register. If two users perform SetTitle ...
Marc's user avatar
  • 11
1 vote

How does Lamport imply anomalous behavior is impossible given these constraints?

The constraint as written by Lamport is $C_i(t+\mu)-C_j(t)\gt0$ or $C_i(t+\mu)\gt C_j(t)$ which can be re-written $$C_i(t+\mu) - C_i(t)\gt C_j(t) - C_i(t) \tag{*}\label{*}$$ Given Lamport's previous ...
NCT's user avatar
  • 21
1 vote

Why does the converse of the clock condition imply that any two concurrent events occur at the same time?

Assume the clock condition AND its converse: $$C(a)\lt C(b) \Rightarrow a \rightarrow b \tag{*}\label{*}$$ Next, take note that $\neg(a \rightarrow b)$ implies either $b \rightarrow a$ or $a \...
NCT's user avatar
  • 21
1 vote
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Calculating CPU throughput on a single cycle vs multicycle datapath

Every instruction in a CPU goes through an Instruction execution cycle. In other words every instruction goes through multiple stages like Fetch,Decode,Execute,Writeresult. In modern processor the ...
ajit's user avatar
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1 vote
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What information needs to be saved in a Lamport clock system to deduce message causality?

Lamport clocks are not designed to allow you to infer all causality. No one ever claimed that knowing the Lamport timestamp is enough to read out the causality of all messages. Rather, Lamport ...
D.W.'s user avatar
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