直写和回写方法的区别

先决条件 – 在缓存中直写和回写

在读操作期间，当 CPU 确定缓存中的一个字时，主存不包括在传输中。因此，当操作是写操作时，系统可以通过两种方式进行。

1. 直写法：最简单的方法是，当缓存在指定地址包含字时并行更新时，每次内存写操作都更新主内存。这可以称为直写方法。

2.回写方法：
在写操作期间，在回写方法中仅更新缓存位置。然后，该位置由一个标志标记，以便稍后在从缓存中删除该字时将其复制到主内存中。对于回写方法，原因是在一个字留在缓存中的时间内，它可以被多次更新。因此，只要该字保留在缓存中，副本是否在主缓存中都没有关系。这只是当字从缓存中移出时，缓存需要重写到主内存中的精确副本。

直写和回写方法的区别：

S.No.	Write Through Method	Write Back Method
1	In this method main memory is updated with every memory write operation as well as cache memory is updated in parallel if it contains the word at the specified address.	In this method only cache location is updated during write operation.
2	Main memory always contains same data as cache.	Main memory and cache memory may have different data.
3	Number of memory write operation in a typical program is more.	Number of memory write operation in a typical program is less
4	When I/O device communicated through DMA would receive most recent data.	When I/O device communicated through DMA would not receive most recent data.
5	It is a process of writing cache and main memory simultaneously.	It is a process of writing cache and data is removed from cache, first copied to main memory.