A disk cache is a small amount of high-speed memory located between the main memory and the hard drive. Its primary purpose is to store frequently accessed data, allowing the computer to retrieve this information more quickly than if it had to read it directly from the slower hard drive. This speeds up overall system performance, especially for tasks that require repeated access to the same data. When a computer needs data, it first checks the disk cache. If the data is found there, it is called a "cache hit," and the system can access it rapidly. If the data is not in the cache, known as a "cache miss," the system must fetch it from the hard drive, which takes more time. This process helps optimize the efficiency of data retrieval in computing systems.