I read a “はじめて読む 486” which describes how the internal system of the 486 works efficiently and how excel it is with comparing to the previous CPU, illustrating the 486 functions.

In this article, I would focus on how cache memory helps to improve the efficiency of data access between the CPU and the main memory. Understanding the flow of operations and the role of cache memory can provide valuable insights into the 486.

The Flow of CPU Operations

When the CPU executes operations, the following flow occurs:

1. Clock Cycle Initiation:
   • The CPU initiates a clock cycle.
2. Address Input:
   • The CPU inputs the address where data is stored into the address bus.
3. Memory Preparation:
   • While the CPU stores data, the memory places the data on the data bus.
4. Data Reading:
   • If the CPU successfully places the address and the memory is ready, the CPU reads the data from the address bus.
5. Handling Memory Delays:
   • If the memory is not ready, the CPU sends a notification indicating the inability to read.
   • The memory then places the data on the address bus, extending the access process.
   • The CPU re-accesses the address bus to read the data.
6. Data Transmission:
   • The memory sends data to the data bus, which the CPU reads.

The Role of Cache Memory

To optimize the above cycle and reduce the data access processing time, cache memory is introduced between the CPU and the main memory. Here’s how it works:

1. Reducing Clock Wait Time:
   • Cache memory helps to shorten the wasted data access processing time and reduces the clock wait time in the cycle.
2. Cache Memory Methods:
   • Write-Through Method: Data is written to both the cache memory and the main memory simultaneously.
   • Write-Back Method: Data is initially written only to the cache memory and written to the main memory at a later time. This method improves read/write (R/W) operation speed but makes it more challenging to maintain consistency between the cache and the main memory.
3. Advantages of Cache Memory:
   • Using cache memory significantly reduces clock wait time, leading to faster and more efficient data access.
   • The write-back method, despite its complexity in maintaining consistency, offers high-speed R/W operations, enhancing overall system performance.

Now that I understood the cache memory efficiency.

In the context of web applications, the concept of caching is widely used. For example, AWS CloudFront’s CDN implements a similar mechanism. Caching is particularly useful for the frontend due to the high volume of user access.

Caching technology can be found in various applications.

1. Content Delivery Networks (CDNs):
   • CDNs, like AWS CloudFront, distribute content to multiple servers across different locations. This allows users to access data from the nearest server, reducing latency and load times.
2. Browser Caching:
   • Web browsers store static files such as HTML, CSS, and JavaScript locally. This means that when a user revisits a website, the browser can quickly load these files from the cache instead of downloading them again from the server.
3. Database Caching:
   • Databases use caching mechanisms like Redis or Memcached to store frequently queried data in memory. This reduces the need to repeatedly access the slower disk storage, improving query response times.
4. Application-Level Caching:
   • Many web applications implement caching at the application level. Frameworks like Django or Laravel have built-in caching systems that allow developers to cache views, queries, and other expensive operations.
5. Operating System Caching:
   • Operating systems use cache memory to store frequently accessed data and instructions. This helps in speeding up processes by reducing the time needed to fetch data from the main memory.

By leveraging caching technology, systems can handle higher loads, deliver content faster, and provide a better user experience overall.