A block whose content has changed memory, but is still not written to disk.

• A. Clean Block
• B. Cached Block
• C. Disk Block
• D. Dirty Block

Answer: (D)

In caching and memory management, a block that has been changed in memory but hasn’t yet been written to disk is called dirty. This label means the in-memory copy is not in sync with the on-disk copy and still needs to be written back at some point to keep data durable. A clean block, by contrast, has no unsaved changes and matches the disk version. A disk block refers to data stored on the hard drive or SSD, not the in-memory modification status. A cached block simply means a copy kept in memory to speed access, but it doesn’t specify whether it has been modified. Dirty blocks are written back when the system evicts the block from cache or flushes caches, ensuring durability even if the in-memory value has diverged from what's on disk.