Home Computer Science What Is Cache Memory In Computer? Understand the Basics

What Is Cache Memory In Computer? Understand the Basics

Cache Memory is a very high-speed memory that is used for synchronizing with the CPU and to speed up the processes. The cache is comparatively costlier than normal disk memory but is more economical than CPU registers. These memories are extremely fast memory, and their main function is to act as a buffer between RAM and CPU. It holds data and instructions that are frequently requested so that they are immediately available to the CPU when needed. The term 'cache' primarily refers to a thing that is hidden or stored somewhere or the place where it is hidden.

Cache memory is a temporary memory officially termed as 'CPU Cache Memory'. Cache memory in your computer is mostly built on top of the processor/CPU chip itself for faster access to data.

Do you know? The term 'cache' in cache memory comes from the French word 'cacher,' which means 'to hide' or 'to conceal.' In the context of computing, cache memory is named so because it hides or conceals the slower main memory (RAM) by storing frequently accessed data closer to the processor.

Types of cache memory 

Cache memory is broadly classified as follows:

  • Primary Cache: The primary cache is located on the processor chip. The cache size is very small and its access time is almost similar to processor registers.
  • Secondary Cache: The secondary cache is placed in the middle of the primary cache and the main memory of the system. It is referred to as L2 (level 2) cache. Most of the time, the L2 cache is housed on the processor chip itself but might be located on a separate chip. L1, L2, and L3 cache are discussed below in this article.

How does cache memory work?

When the CPU requests data or data is required by the CPU, it will automatically turn to the cache memory for accessing data fast and economically. Cache storage is a temporary storage like RAM. This is required because system RAM is slower and is a bit further away from the CPU, and all of this has a huge impact on performance and latency when data needs to be accessed frequently. When data is found in cache memory, this is called a cache hit.

Hit ratio = hit / (hit + miss) = no.

A cache hit enables the processor to retrieve data quickly, making your overall system more efficient and faster.

Also, cache memory is very much smaller than system RAM and it can only store data temporarily, so it may not hold the information that the processor needs sometimes. When the cache does not have the processor’s required data, this is called a cache miss, and in this case, the CPU has to move onto the hard drive and use RAM.

Cache versus RAM

RAM(Random Access Memory)/Main Memory or also called primary memory is a volatile memory with a larger size that can store the data as long as the power is supplied. It is comparatively costlier than cache memory because it is based on high-speed SRAM random access memory which is faster, expensive, and less dense. It is a slower memory compared to cache. But RAM is faster than a hard disk, floppy disk, compact disk, or just any form of secondary memory storage media. CPU reads cache memory data before reading RAM, and if data is unavailable in cache it impacts CPU performance. A plus point of RAMs is they can be installed both internally and externally.

On the other hand, the size of cache memory is very less compared to RAM memory and it holds data that the CPU needs to access frequently. It is very fast compared to RAM. Cache memory is basically used for faster access time of the data, as the CPU first accesses cache memory before turning towards RAM.

As we all know, RAM is also the main memory of the computer, and all of the functions are executed from RAM itself, but these days super-fast SSDs are capable of memory swapping. Therefore, these ROM memories are also becoming capable of supporting functions when the system experiences a RAM shortage.

Parameter Cache Memory RAM

Size

Small in size

Larger in size

Location

Located closer to the CPU

Located farther from the CPU

Speed

Faster access speed

Slower access speed

Cost

Expensive

 

Relatively cheaper

Storage

Stores frequently accessed data

Stores data currently in use by the CPU

Capacity

Lower capacity

Higher capacity

Function

Helps reduce the CPU's workload

Provides temporary storage for data and instructions

Access

Not directly accessible by the user

Directly accessible by the user

Cache versus Virtual Memory

Virtual memory is basically nothing but a logical unit of computer memory that increases the capacity of main memory by executing programs of larger size than the main memory in the computer system. Virtual memory comparatively has a very large size compared to cache memory. Although virtual memory is helpful, it is not defined as an actual memory unit. The virtual memory is not hardware-controlled but instead controlled by the Operating System (OS). It requires a mapping structure to map the virtual address with a physical address.

Criteria Cache Memory Virtual Memory
Definition A small, high-speed memory located on the CPU that stores frequently accessed data and instructions for quick access. An extension of the computer's physical memory, which uses a portion of the hard drive as an overflow storage for data that cannot fit into RAM.
Size Smaller in size compared to main memory (RAM). Larger in size compared to cache memory and main memory (RAM).
Speed Extremely fast access time, as it is located on the CPU. Slower access time compared to cache memory, as it resides on the hard drive.
Purpose To reduce the average time taken to access data and instructions by storing frequently used data closer to the CPU. To provide additional memory space when the physical RAM is insufficient to hold all the running programs and data.
Volatility Volatile memory, meaning its contents are lost when the power is turned off. Non-volatile memory, meaning its contents are retained even when the power is turned off.
Cost Expensive due to its high-speed and small size. Relatively cheaper compared to cache memory, as it utilizes the hard drive for storage.

Levels of Cache Memory

Computer systems these days have more than one level of cache memory, and they are variable in size and proximity to the processor cores and processing speed. They are also called cache levels. Let’s have a look at types of cache memory :

  • Level 1: L1 cache is a type of memory that's built into the CPU chip itself. It's typically the fastest cache memory and consumes a limited amount of space. In most modern CPUs, it's divided into two parts: the data section and the instruction section. Since it's very fast, the L1 cache is the first place a processor will look for traces of data or instructions that have been buffered in RAM. In most modern CPUs, the data section and the instruction section are divided into two. The modern CPU typically has a cache size of 32 KB.
  • Level 2: L2 memory cache can also be found in the CPU's cache but might be located on a separate chip close to the CPU. L2 cache size is typically larger than the L1 cache and can be found in the order of 256K bytes per core.
  • Level 3: Level 3 cache is typically much larger cache than L1 or L2 cache, but it differs in another significant manner. Unlike the L1 and L2 caches, which are private to each CPU core, the L3 cache is often shared by all cores. As a result, it can play a crucial role in data exchange and inter-core communication. The L3 cache per core could be on a scale of 2 MB cache.

Cache Mapping

As previously stated, cache memory is incredibly fast - meaning it can be read from very quickly. However, there is a bottleneck: data must first be located before it can be read from cache memory. The CPU is aware of the data or instruction address in RAM memory that it wishes to read. It must search the memory cache for a reference to that RAM memory location in the memory cache, as well as the data or instruction associated with it.

Data or instructions from RAM can be mapped into memory cache in a variety of ways, each of which has a direct impact on the speed with which they can be found. However, there is a cost: reducing the amount of time spent on searching also minimizes the likelihood of a cache hit, while maximizing the chances of a cache hit maximizes the search time.

The common cache mapping methods are:

1. Direct Mapping

With a direct-mapped cache, a given block of RAM data can only be stored in one location in cache memory. This means that the CPU only needs to check one location in the memory cache to determine if the data or instructions it seeks are present, and if they are, they will be discovered quickly. The disadvantage of direct-mapped cache is that it significantly restricts the types of data or instructions that can be placed in the memory cache, making cache hits infrequent.

2. Associative Mapping

This is the polar opposite of direct mapping and is also known as fully associated mapping. Any block of data or instructions from RAM can be placed in any cache memory block using an associative mapping mechanism. That means the CPU must explore the full cache memory to check if it contains the information it seeks, but the chances of finding it are significantly higher.

3. Set-Associative Mapping

Set associative mapping, which allows a block of RAM to be mapped to a limited number of different memory cache blocks, is a compromise between the two methods of mapping. A RAM block can be placed in one of two locations in cache memory using a 2-way associative mapping method. An 8-way associative mapping scheme, on the other hand, would allow a RAM block to be placed in any of the cache memory blocks. Because the CPU has to seek in two places instead of just one, a 2-way system takes twice as long to search as a direct-mapped system, but there is a significantly higher possibility of a cache hit.

Summing Up

We can conclude that the presence of cache memory improves computers in terms of speed and performance as they are able to access data much faster compared to RAM and Local Disk. A 6MB cache is a decent size, but we can conclude that 8MB is much better. Hence, the more, the better, as cache is the fastest memory in a computer. The larger the size, the more efficient and faster the CPU is. However, it must be noted that there is no impact on CPU clock speed.

Frequently Asked Questions Regarding Cache Memory

1. What is cache memory and why is it important?

Cache memory is a small, high-speed memory located on the processor chip or between the processor and main memory. It stores frequently accessed data and instructions, allowing the processor to quickly retrieve them when needed. Cache memory plays a crucial role in improving the overall performance and speed of a computer system.

2. How does cache memory work?

Cache memory operates on the principle of locality, which means that programs tend to access the same data and instructions multiple times. When the processor needs to fetch data, it first checks the cache. If the required data is found in the cache, it is called a cache hit, and the processor can access it quickly. If the data is not present in the cache, it is called a cache miss, and the processor has to retrieve it from the slower main memory.

3. What are the different levels of cache memory?

Cache memory is organized into multiple levels, commonly referred to as L1, L2, and L3 caches. L1 cache is the smallest but fastest cache located closest to the processor. L2 cache is larger and slightly slower than L1 cache, while L3 cache is even larger but slower than both L1 and L2 caches. The hierarchy allows for a trade-off between speed and capacity, ensuring that frequently accessed data is stored in faster caches.

4. How does cache memory impact system performance?

Cache memory significantly impacts system performance by reducing the time it takes for the CPU to access data. With data stored in cache, the CPU can fetch it quickly without waiting for slower main memory access. This leads to faster execution of instructions and overall improved system responsiveness. A larger cache size and higher cache hit rate generally result in better performance.

5. Can cache memory be upgraded or expanded?

Yes, cache memory can be upgraded or expanded in some cases. However, it depends on the specific hardware and its design. Some processors allow for upgrading or expanding cache memory, while others do not. It is important to check the specifications of your device or consult with a professional to determine if cache memory can be upgraded or expanded.

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Shreeya Thakur
Sr. Associate Content Writer at Unstop

I am a biotechnologist-turned-content writer and try to add an element of science in my writings wherever possible. Apart from writing, I like to cook, read and travel.

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Updated On: 27 Nov'23, 01:32 AM IST