What is Refresh Cycle? (Explained)

What is Refresh Cycle?

A refresh cycle, with reference to computer memory, signifies the process of recharging the memory cells of the module. And, in terms of other computer hardware, it represents the time interval between replacements.


  • A refresh cycle is usually a process involving the DRAM modules because their circuit design results in a charge drain or decay.
  • It is good to refresh the memory cells on a regular basis as it will prevent data loss.
  • Refreshing happens continually, usually after every 64 milliseconds and takes very little time.
  • Typically, Static RAM modules do not need refreshing because their circuit design does not cause charge drain.

Understanding Refresh Cycle

Understanding Refresh Cycle

The refresh cycle is a process typically followed to refresh the memory cells.

Ideally, data is stored on the memory as binary digits, such as:

  • 0, signifying ‘off,’ and does not need any electrical charge.
  • 1, signifying ‘on,’ state, and needs electrical charge to turn on the electronic switches to store data.

This continual change in the states may result in charge drain and loss of data, which is why it is needed to refresh the memory cells.

The design of the DRAM architecture results in charge decay and therefore needs refreshing on a regular basis so that data can be stored in it for a long period of time.

Refresh cycle, which typically involves recharging the cells with the necessary electrons. This process is undergone in the Random Memory Access (RAM) occasionally.

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Typically, in this process, the information stored in the memory is read and then rewritten. This ensures that it will not disappear even after a charge drain.

What is Refresh Cycle


Usually, the DRAM cells are refreshed independently after every 64 milliseconds. However, it may be halved if the temperature is high.

This means that there will be a performance hiccup after 64 milliseconds when the cells are being refreshed and during this time the memory is usually inaccessible.

Therefore, the performance of the memory module will typically depend on how exactly it is designed for refreshing the individual memory cells.

The good thing is that the memory controller times these refresh cycles so that they occur only when the memory module is doing other things than reading or writing, for example, transmitting data.

However, refreshing the memory cells needs little time, often ranging between 75 and 120 nanoseconds, which means that it would take anywhere between 0.4% and 5% roughly of the time taken to perform a refresh operation.


The memory refresh cycle is a very helpful technique for:

  • Preventing data loss or leakage
  • Ensuring the data in the memory is stored properly
  • Warranting that the bits stored in the memory module are not read erroneously

Without the refresh cycle being performed repeatedly, the data will be lost in just a few milliseconds.


The operation is quite simple and everything happens automatically. The memory controller oversees the process without the CPU being conscious of it.

An entire row is refreshed at once with smaller and more effective signals instead of reading a particular column in the row.

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The data is read into the sense amplifiers and back into the cells straightaway instead of going through the output buffers, which would have made the process relatively slow.


Depending on the circuit, the refresh cycle can be of different types, such as:

  • Burst refresh
  • Distributed refresh
  • RAS only refresh
  • CAS before RAS refresh
  • Hidden refresh


Refresh comes with an overhead, which is the time taken by the memory module and is calculated as follows:

refresh overhead = time required for a refresh/ refresh interval

Here, the time required for refresh is the product of length of refresh cycle and the rows.

How Long Does the Refresh Cycle Last?

Usually, a refresh cycle would last for about five years on an average. Typically, a refresh cycle may last anywhere from 3 to 5 years, but in some cases, it can be as long as 8 years, depending on how well a system is maintained.

With respect to a server refresh cycle, it is actually the measure of the length of time or the interval between installing a new server and its allied hardware in a data center.

However, this time period may vary depending on the replacement cycle followed by different businesses.


It must be clear to you now that the refresh cycle is a process typically followed in the DRAM modules to rejuvenate the memory cells after a charge decay. The process is simple and useful as it prevents data loss.

The refresh working process may, however, vary based on the type of counter circuits in the memory circuitry.

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