A computer uses different types of storage arranged in a hierarchy. (a) The diagram shows a storage hierarchy. State the relationship between speed and capa...

(a) As you move down the storage hierarchy (from registers at the top, through cache, RAM, and down to secondary storage at the bottom):

• Storage capacity increases. [1] Registers hold only a few bytes, whereas a hard drive can hold terabytes.
• Speed of access decreases. [1] Registers operate at the speed of the CPU clock, while secondary storage involves much slower read/write operations.

This trade-off exists because the fastest memory technologies are extremely expensive to manufacture, so they are only used in small quantities close to the processor.

(b) Cache memory stores copies of frequently accessed data and instructions from RAM. [1] By holding this data in a faster memory layer between the CPU and RAM, the processor can retrieve it much more quickly than if it had to fetch it from the slower main memory every time. [1] This significantly speeds up processing because the CPU spends less time waiting for data.

(c) A computer needs both RAM and secondary storage because they serve complementary roles:

• RAM is needed to temporarily hold the programs and data the processor is currently working with, providing fast access during execution. [1]
• Secondary storage is needed to permanently store the operating system, applications, and user files, because RAM is volatile and loses all its contents when the power is turned off. [1]

(d) Virtual memory is an area of secondary storage (such as part of a hard drive or SSD) that the operating system uses as an extension of RAM when physical RAM becomes full. [1] When all RAM is in use, the operating system moves less frequently used pages of data from RAM to the virtual memory area on disk, freeing up RAM for active tasks. Although this prevents the system from running out of memory, accessing data from virtual memory is considerably slower than accessing real RAM because it involves reading from secondary storage. [1]