# Questions tagged [clocks]

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### How do computers keep track of time?

How are computers able to tell the correct time and date every time? Whenever I close the computer (shut it down) all connections and processes inside stop. How is it that when I open the computer ...
8k views

### Clock synchronization in a network with asymmetric delays

Assume a computer has a precise clock which is not initialized. That is, the time on the computer's clock is the real time plus some constant offset. The computer has a network connection and we want ...
51k views

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

While reading a book, I came across a paragraph given below: In order to synchronize all of a computer’s operations, a system clock—a small quartz crystal located on the motherboard—is used. The ...
800 views

### All soldiers should shoot at the same time

When I was a student, I saw a problem in a digital systems/logic design textbook, about N soldiers standing in a row, and want to shoot at the same time. A more difficult version of the problem was ...
2k views

### Happened-before and Causal order

I'm reading Lamport's "Time, Clocks, and the Ordering of Events in a Distributed System" and there's a detail that's bugging me. Lamport defines the "happened before" partial order, which I ...
676 views

### Lamport Timestamps: When to Update Counters

In the timepiece (excuse the pun) that is Time, Clocks and the Ordering of Events, Lamport describes the logical clock algorithm as the following: Each process $Pi$ increments $Ci$ between any two ...
585 views

### Visualization of Lamport's three-dimensional “space-time diagram” with introduced “tick lines”

In the third page (the third paragraph in the right column) of the paper "Time, Clocks, and the Ordering of Events in a Distributed System" by Leslie Lamport, it says that The reader may find it ...
86 views

### What is 2g-precedence?

I am currently reading a couple of papers about event processing. In the context of ordering events, "2g-precedence" is frequently mentioned. I don't know what it is, and I cannot find much ...
2k views

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

I am currently trying to understand how Computers are arranged and organized internally (so that I can learn Assembly Language) through an online book called The Art of Assembly by Randall Hyde. ...
697 views

### Vector clocks: Why is it necessary to increment my clock on receiving a message?

Assume I have a distributed system of entities, each with a replica of the same data object that can be modified by broadcasting the changes and I'm using vector clocks to know how to order changes. ...
326 views

### Is there a way to compute time without system clock

I was thinking about any method where we can use RAM I/O speed, to calculate time, let's say for example: RAM transfer rate is 1000 MB/s, so when it's half full (about 500 M Bytes written), by ...
137 views

### Are vector clocks useful in centralized systems?

Vectors clocks seem to be a common way to synchronize the partial ordering of events in a distributed, peer-to-peer, system across all clients. Is there any benefit to using them in a centralized ...
960 views

### How is clock syncing implemented?

I'm looking for an explanation or reference on the implementation of computer clock. To keep the question at the level of logical abstractions: say, we put together some combinational and sequential ...
646 views

### How are lamport timestamps useful in practice?

I am reading Lamport's paper titled Time, clocks, and the ordering of events in a distributed system I understand what's in there more or less, but I am confused whether Lamport timestamps on their ...
612 views

### How can I calculate the effective bandwidth of a memory system?

I am currently doing my homework for my Computer Architecture class. One of the questions asks: A computer has a 64-bit data bus and 64-bit-wide memory blocks. The memory devices have an access ...
129 views

### Lamport logical clock: what does partial mean in the concept of Partial ordering?

In lamport's paper[1], he define two concept The partial ordering and The totally ordering. What does partial mean in ...
62 views

### Lamport logical clock: why event occurs in a process with smaller pid is treated earlier?

In lamport's paper1, he define global local timestamp, which is composed of process id and local lamport timestamp. This timestamp is used to order all the events in a distributed system. The rule ...
53 views

### Why is an accurate time so important for servers and computers?

I just saw this short documentary about atomic clocks. The person working for the Atom clock company gets asked what would happen is all the atom clocks would be turned off and he replayed that cell ...
145 views

### Applying information theory to processor clocks

Has there been any research on the subject of applying information theory to a processors clock? It occurred to me that a clock is actually transmitting data that is used for synchronization of ...
46 views

### Whats the point of caching if the minimum single clock cycle time is the prorogation delay of the slowest component (fetching from DRAM)?

I know that the clock speed is determined by the slowest stage within the processor (usually fetch) because one clock cycle will take as much time as the slowest pipeline stage to ensure everything is ...
3k views

### Clock skew vs clock offset in the context of clock synchronization network protocols

In the context of clock synchronization among nodes of a network, what is clock offset and what is clock skew? Are these terms synonymous or is there a difference between them?
64 views

### What information needs to be saved in a Lamport clock system to deduce message causality?

By using Lamport timestamps, we can determine the causality of messages. It is however unclear to me how one would deduce this simply from the lamport timestamp of the message. Take the following ...
185 views

### calculate average CPI [closed]

I cannot solve this exercise: "If a processor has a cache hit rate of 99.5% and a cache miss penalty of 160 core processor cycles, what will the average CPI be for 1,000 instructions?" how can i do ...
75 views

### Processor system synchronization?

Processor has the internal clock which is a multiplier of the main clock which is present on the motherboard which is designed by keeping in mind the critical path and the slowest device on board, ...
169 views

### Is potential causality relation equals to set of consistent happens before relations?

In a book dedicated to distributed algorithms, I found the following definition - potential causality diagram is consistent with happens before diagram if potential causality relation between system ...
238 views

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

Singhal–Kshemkalyani’s differential technique is based on the observation that between successive message sends to the same process, only a few entries of the vector clock at the sender process ...
64 views

### How do computers synchronize their clocks with the standard time

I'd like to know how clock synchronization is done on computers, I've read this wikipedia article however it didn't give me exactly what I was looking for, I'll outline the problem I'd like answered: ...
26 views

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

If two computer system's has to do some kind communication like data transfer or receiving should its clock sync to do that?If not then how they transfer bytes without having syced clocks?
66 views

### How can one tell when will the state of the circuit components change? [closed]

The system clock is needed to synchronize all components on the motherboard, which means they all do their work only if the clock is high; never when it's low. And because the clock speed is set above ...