Difference Between Cache Memory and Virtual Memory

The main difference between cache memory and virtual memory is that cache memory is a storage unit that stores copies of data from frequently used main memory locations so that the CPU can access that data faster while virtual memory is a memory management technique that allows the user to execute programs larger than the actual main memory.

Memory is an important component in the computer. There are several types of memory; cache memory and virtual memory are two of them. Cache memory is a component that is used by the CPU to reduce the average time to access data from the main memory. It is smaller than the main memory, but it is very fast. On the other hand, virtual memory is a logical memory. Usually, the user programs are large than the main memory. Virtual memory extends the capacity of the main memory so that the user can execute large programs. In brief, the cache memory is a storage unit while virtual memory is a memory management technique handled by the operating system.  

Key Areas Covered

1. What is Cache Memory
     – Definition, Functionality
2. What is Virtual Memory
     – Definition, Functionality
3. Difference Between Cache Memory and Virtual Memory
     – Comparison of Key Differences

Key Terms

Cache Memory, Virtual Memory, Operating System

What is Cache Memory

There are various types of memory. The CPU registers are the fastest. The cache memory is slower than CPU registers but faster than the main memory. Therefore, the frequently used data by the CPU is stored in the cache memory. The data transferring rate from the cache memory to CPU is fast. The blocks inside the cache are known as cache lines.  When the data required by the CPU is available in the cache memory, it is called a cache hit. When the required data is not available in the cache, it is called a cache miss, and that data is brought from the main memory to CPU.

Figure 1: Cache Memory Organization

There are two types of cache memory organizations. In a single level cache organization, there is a single cache. The main memory transfers blocks to cache while the cache transfers words to the CPU. In a multi-level cache organization, there are three types of cache available. They are called Level 1 (L1), Level 2 (L2) and Level 3 (L3) cache. L1 is the smallest cache while L3 is the largest cache. The most frequently used data resides in L1. The data transferring rate from the Level 1 cache to CPU is the fastest.

Overall, cache memory stores the data CPU requires the most. It takes a lower amount of time for the CPU to access the cache memory than accessing the main memory.

What is Virtual Memory?

The virtual memory is a logical memory. It is a memory management technique handled by the operating system. Virtual memory allows the programmer to use more memory for a program than the available main memory. For example, assume that a computer has a main memory of 4GB and a virtual memory of 16GB. The user can use this 16GB to execute the program. Therefore, the user can execute programs which require more memory than the capacity of the main memory.

Figure 2: Virtual Memory

Overall, virtual memory provides two advantages. A program is larger than physical memory. The virtual memory allows using memory more than the available main memory. Moreover, it avoids accessing the main memory directly. When using the virtual memory, the virtual addresses are translated into the corresponding physical address. Therefore, it implements memory protection.

Difference Between Cache Memory and Virtual Memory

Definition

Cache memory is a small memory type that provides high-speed data access to a CPU and stores frequently data. Virtual memory is a memory management technique that creates an illusion to users of a larger main memory.

Basis

The cache memory is a storage unit. Therefore, it is a hardware component. Virtual Memory is a memory management technique. It is handled by the operating system.

Usage

CPU takes more time to access the main memory. But storing the data in the cache allows the CPU to access data in a minimum time. On the other hand, the virtual memory allows the user to execute programs that are larger than the capacity of the main memory.

Size

The cache memory is smaller in size while the virtual memory is larger in size.

Speed

Cache memory is faster than the virtual memory.

Conclusion

The difference between cache memory and virtual memory is that the cache memory is a storage unit that stores copies of data from frequently used main memory locations so that the CPU can access that data faster while the virtual memory is a memory management technique that allows the user to execute programs larger than the actual main memory.

Reference:

1. Introduction to Cache Memory, Tutorials Point (India) Pvt. Ltd., 24 Jan. 2018, Available here.
2. Virtual Memory, Tutorials Point (India) Pvt. Ltd., 18 Jan. 2018, Available here.

Image Courtesy:

1. “Virtual memory” By Ehamberg – Own work (CC BY-SA 3.0) via Commons Wikimedia