Tag: cache memory notes

Cache Memory in Computer Architecture

Computer Organization and Architecture

Cache Memory-

 

  • Cache memory is a Random Access Memory.
  • The main advantage of cache memory is its very fast speed.
  • It can be accessed by the CPU at much faster speed than main memory.

 

Location-

 

  • Cache memory lies on the path between the CPU and the main memory.
  • It facilitates the transfer of data between the processor and the main memory at the speed which matches to the speed of the processor.

 

 

  • Data is transferred in the form of words between the cache memory and the CPU.
  • Data is transferred in the form of blocks or pages between the cache memory and the main memory.

 

Purpose-

 

  • The fast speed of the cache memory makes it extremely useful.
  • It is used for bridging the speed mismatch between the fastest CPU and the main memory.
  • It does not let the CPU performance suffer due to the slower speed of the main memory.

 

Execution Of Program-

 

  • Whenever any program has to be executed, it is first loaded in the main memory.
  • The portion of the program that is mostly probably going to be executed in the near future is kept in the cache memory.
  • This allows CPU to access the most probable portion at a faster speed.

 

Step-01:

 

Whenever CPU requires any word of memory, it is first searched in the CPU registers.

Now, there are two cases possible-

 

Case-01:

 

  • If the required word is found in the CPU registers, it is read from there.

 

Case-02:

 

  • If the required word is not found in the CPU registers, Step-02 is followed.

 

Step-02:

 

  • When the required word is not found in the CPU registers, it is searched in the cache memory.
  • Tag directory of the cache memory is used to search whether the required word is present in the cache memory or not.

 

Now, there are two cases possible-

 

Case-01:

 

  • If the required word is found in the cache memory, the word is delivered to the CPU.
  • This is known as Cache hit.

 

Case-02:

 

  • If the required word is not found in the cache memory, Step-03 is followed.
  • This is known as Cache miss.

 

Step-03:

 

  • When the required word is not found in the cache memory, it is searched in the main memory.
  • Page Table is used to determine whether the required page is present in the main memory or not.

 

Now, there are two cases possible-

 

Case-01:

 

If the page containing the required word is found in the main memory,

  • The page is mapped from the main memory to the cache memory.
  • This mapping is performed using cache mapping techniques.
  • Then, the required word is delivered to the CPU.

 

Case-02:

 

If the page containing the required word is not found in the main memory,

  • A page fault occurs.
  • The page containing the required word is mapped from the secondary memory to the main memory.
  • Then, the page is mapped from the main memory to the cache memory.
  • Then, the required word is delivered to the CPU.

 

Multilevel Cache Organization-

 

  • A multilevel cache organization is an organization where cache memories of different sizes are organized at multiple levels to increase the processing speed to a greater extent.
  • The smaller the size of cache, the faster its speed.
  • The smallest size cache memory is placed closest to the CPU.
  • This helps to achieve better performance in terms of speed.

 

Example-

 

Three level cache organization consists of three cache memories of different size organized at three different levels as shown below-

 

Size (L1 Cache) < Size (L2 Cache) < Size (L3 Cache) < Size (Main Memory)

 

 

To gain better understanding about Cache Memory,

Watch this Video Lecture

 

Next Article- Cache Mapping Techniques

 

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