On the first read for a block that is not cached, where does the data come from?

On the first read for a block that is not cached, where does the data come from?

• A. The origin
• B. Another cache
• C. The read fails
• D. Cache returns zeros

Answer: (A)

When a block isn’t in the cache, the read is served from the origin—the back-end storage where the actual data lives. The cache holds nothing for that block yet, so the system retrieves it from origin, returns the data, and typically caches it for faster future access. This is why the first read comes from origin rather than from cache. The other options don’t fit: there isn’t another cache supplying the data in this scenario, the read doesn’t fail by default, and the cache wouldn’t just return zeros on a normal miss.

When a block isn’t in the cache, the read is served from the origin—the back-end storage where the actual data lives. The cache holds nothing for that block yet, so the system retrieves it from origin, returns the data, and typically caches it for faster future access. This is why the first read comes from origin rather than from cache. The other options don’t fit: there isn’t another cache supplying the data in this scenario, the read doesn’t fail by default, and the cache wouldn’t just return zeros on a normal miss.