What is CACHE?

𝑾𝒉𝒂𝒕 𝒊𝒔 𝑪𝒂𝒄𝒉𝒆 𝒂𝒏𝒅 𝑾𝒉𝒂𝒕 𝒊𝒔 𝑰𝒕𝒔 𝑷𝒖𝒓𝒑𝒐𝒔𝒆?

In the realm of computing, especially in the embedded industry, the term “cache” holds significant importance. But what exactly is a cache? Why do our systems require it?

𝑫𝒆𝒇𝒊𝒏𝒊𝒕𝒊𝒐𝒏 𝒂𝒏𝒅 𝑩𝒂𝒔𝒊𝒄 𝑷𝒓𝒊𝒏𝒄𝒊𝒑𝒍𝒆𝒔

𝑪𝒂𝒄𝒉𝒆 – A cache is a smaller, faster type of volatile computer memory that provides high-speed data access to a processor and improves its speed and performance. The primary purpose of the cache is to store program instructions and data that are used repeatedly in the operation of programs or information retrieval. It acts as a buffer between the main memory and the CPU, bridging the performance gap between high-speed processors and slower main memory.

𝑷𝒓𝒊𝒏𝒄𝒊𝒑𝒍𝒆 𝒐𝒇 𝑳𝒐𝒄𝒂𝒍𝒊𝒕𝒚: Caching leverages the principle of locality, which states that if a particular memory location is accessed, then there’s a high probability that nearby memory locations will be accessed in the near future.

There are two main types of locality:

Temporal Locality: If a memory location is accessed, it will likely be accessed
again in the near future.

Spatial Locality: If a memory location is accessed, nearby memory locations are likely to be accessed soon. (more in comment section)

𝑩𝒆𝒏𝒆𝒇𝒊𝒕𝒔 𝒂𝒏𝒅 𝑻𝒓𝒂𝒅𝒆-𝒐𝒇𝒇𝒔 𝒐𝒇 𝑪𝒂𝒄𝒉𝒊𝒏𝒈

𝑩𝒆𝒏𝒆𝒇𝒊𝒕𝒔 :

Speed: Cache memory provides faster data storage and access by storing instances of programs and data routinely accessed by the processor.

Reduced Latency: On average, accessing the main RAM can take up to 60 times longer than accessing the cache. By leveraging cache memory, data access speeds can improve significantly.

Efficiency: By minimizing the number of times the processor has to read from the main memory, cache memory enhances system efficiency.

𝑻𝒓𝒂𝒅𝒆-𝒐𝒇𝒇𝒔:

Size vs. Speed: Larger caches can store more data but may have slower access times. Smaller caches are faster but can store less data.

Complexity: Implementing cache requires additional hardware, algorithms for managing the cache, and sometimes, software support.

Cost: Cache memory is faster and more expensive than main memory, increasing the overall cost of the system.

Coherency Challenges: In multi-core systems, ensuring that all cores have a consistent view of memory can be challenging.

Embedded systems often execute repetitive tasks and they would highly benefit from usage of cache. Utilizing both temporal and spatial locality ensures that these systems can perform their tasks with higher efficiency and speed.

Some Terminology
Temporal Locality:

Imagine you’re working on an embedded system where a sensor reads data every millisecond. If you access the sensor’s value at one instance, the chances are that you’ll access it again very soon. This frequent access to the same memory location over a short span showcases temporal locality. In terms of caching, it means if a specific memory location is accessed, it’s a good idea to keep that data in the cache for a short while.

Spatial Locality:

Consider a program running on an embedded system. The instructions of this program are stored in consecutive memory locations. When one instruction is fetched into the cache, it’s beneficial to fetch the subsequent instructions as well. This behavior, where accessing a memory location gives a high probability of accessing nearby memory locations soon, demonstrates spatial locality.

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