A disk or memory cache that supports writing. Data normally written to memory or to disk by the CPU is first written into the cache. During idle machine cycles, the data are written from the cache memory to main memory or to disk. Write-back caches improve performance, because writing to the cache is faster than writing to main memory or disk. Disk Writes A disk write-back cache does add a slight amount of risk, because the data remain in volatile memory longer. When the computer is turned off, the operating system ensures that the data written to the cache are saved before powering down. See write-through cache and cache.