Answer:
The missing word is backing store.
Explanation:
A backing store is a device for secondary storage of data that typically has greater capacity than the primary store but is slower to access.
A process must be loaded into memory in order to execute.
If there is not enough memory available to keep all running processes in memory at the same time, then some processes who are not currently using the CPU may have their memory swapped out to a fast local disk called the backing store.
The backing store may be the Hard Disk Drive or a Universal Serial Bus Drive. The backing store can sometimes be referred to as virtual memory.
This memory that appears to exist as main storage although most of it is supported by data held in secondary storage, transfer between the two being made automatically as required.
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