Definition of:write back cache
write back cache

A disk or memory cache that supports the caching of 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 into memory or onto disk. Write back caches improve performance, because a write to the high-speed cache is faster than to normal RAM or disk.

Write Back Adds a Delay
A write back cache for disks adds a slight amount of risk, because the data remain in volatile memory longer. At shut down, the operating system typically adds a small delay to ensure the write cache is emptied. If it is necessary to turn the computer off in a hurry because of an imminent loss of power, a write back cache will keep data in memory for a couple extra seconds before being saved to disk. See write through cache.