Difference between writeback and write through cache

Write-through

When you update data, the system writes it to both the cache and the back-end storage. This mode makes operations easy, but it slows down data writing because the data has to be written to both the cache and the storage.

Write-back

When you update data, it is written only to the cache. The modified data is saved to the back-end storage only when the data is removed from the cache. This mode offers fast data write speed, but there is a risk of data loss if a power failure happens before the updated data is written to the storage.

Differences Between Write-Through and Write-Back Methods

1. Write-Through Method:
   • In this method, both the main memory and cache memory are updated simultaneously when a memory write operation occurs.
   • If the cache memory contains the data at the specified address, it is updated in parallel with the main memory.
2. Write-Back Method:
   • In this method, only the cache location is updated during a write operation.
   • The main memory and cache memory may have different data since the update is not immediately reflected in the main memory.
3. Frequency of Memory Write Operations:
   • The write-through method typically involves a higher number of memory write operations in a typical program.
   • The write-back method generally has fewer memory write operations in a typical program.
4. I/O Device Communication through DMA:
   • When an I/O device communicates through Direct Memory Access (DMA), it receives the most recent data in the write-through method.
   • In the write-back method, the I/O device communicating through DMA may not receive the most recent data since it is only updated in the cache.
5. Writing Process:
   • Write-through is a process of simultaneously writing data to both the cache and main memory.
   • Write-back is a process where data is written to the cache, and when it is removed from the cache, it is first copied to the main memory.

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