Difference between Associative Mapping and Direct Mapping in Cache

This article gives the brief explanation about the Associative and Direct mapping techniques. We will get a brief understanding about associative and direct mapping after going through this article.

What is Associative Mapping?

Associative mapping can be defined as a mapping technique in which the memory block in the main memory can be mapped with any of the line available in the cache memory. It is an improved mapping technique, and it helps in overcoming the problems or the drawbacks present in the direct mapping technique.

In associative mapping, there will be no placement restrictions such as the memory block from the main memory that can map with any of the line in cache which is not mapped with other memory block i.e., the lines that are empty in the cache memory.

What is Direct Mapping

Direct mapping can be defined as a mapping technique in which each memory block maps with exactly one cache. For each line in the main memory, CPU holds the tag bits. The direct mapping is a procedure or a process of providing a line in the cache for the blocks of main memory. The procedure includes different calculations, and it makes the memory to allocate properly between cache memory and main memory in the CPU. In the direct mapping, there will be restriction on the placement of the memory blocks in cache memory. Tag, Block and word are the main parts of the main memory block. Each and every part has its own importance. They all carry some information about the data present in the block.

Advantages of Associative mapping

• The associative mapping is fast when compared to other mapping techniques.
• The associative mapping is easy to work and implement.
• The associative mapping has more advantages than the direct mapping technique.
• The major advantage of the associative mapping is that there will be no placement restrictions to map the main memory block with cache memory line. The main memory block can map with any block that present in the cache memory.

Advantages of Direct Mapping

The direct mapping got great advantages. It is one of the simplest types of mapping techniques. It is fast because it only checks that the tag field is matched or not. The direct mapping is less expensive than the other mapping techniques.

Disadvantages of Associative Mapping

• Associative mapping stores the address along with the components or data field.
• It uses lots of extra space to store both of them.
• The Associative mapping is costlier when compared to other mapping techniques.

Disadvantages of Direct Mapping

• Direct mapping provides low performance when compared to associative mapping.
• Every memory block will be assigned with a specific block in cache memory that the memory block should only map with the assigned block in the cache memory.

Differences between Associative Mapping and Direct Mapping in Tabular Form

Associative Mapping	Direct Mapping
Associative mapping is the most flexible cache organization and the fastest cache organization technique.	The direct mapping performs less flexible because there will be replacement for every data tag value.
The associative mapping stores both the address and the data or the content of the memory block.	In direct mapping, the address is stored into three parts i.e. Tag, Block and word.
The associative mapping is easy to implement than the direct mapping.	Direct mapping is a bit cheaper than the associative mapping because it uses RAM, and it uses less storage.
The memory blocks of the main memory can be mapped with any block or line present in the cache memory.	The memory block of the main memory can only map with the one possible location.
The associative mapping needs to compare all the tag bits present in the memory.	Every word in the cache consists of the data word and its associated tag.
In the associative mapping, the main memory block has the address that is divided into two parts namely tag.	The main memory address is mainly divided into three parts i.e. Tag, Block and word.