About Ram & Secondary Storage

Question

Why do Ram size is always smaller than Secondary Storage(HDD/SSD)? If you observe any device you will get the same question

Answer 1

Why do Ram size is always smaller than Secondary Storage(HDD/SSD)? If you observe any device you will get the same question

The primary reason is price. For example (depending a lot on type, etc) currently RAM is around $4 per GiB and "rotating disk" HDD is $0.04 per GiB, so RAM costs about 100 times as much per GIB.

Another reason is that HDD/SSD is persistent (the data remains when you turn the power off); and the amount of data you want to keep when power is turned off is typically much larger than amount of data you don't want to keep when power is turned off. A special case for this is when you put a computer into a "hibernate" state (where the OS stores everything in RAM and turns power off, and then when power is turned on again it loads everything back into RAM so that it looks the same; where the amount of persistent storage needs to be larger than the amount of RAM).

Another (much smaller) reason is speed. It's not enough to be able to store data, you have to be able to access it too, and the speed of accessing data gets worse as the amount of storage increases. This holds true for all kinds of storage for different reasons (and is why you also have L1, L2, L3 caches ranging from "very small and very fast" to "larger and slower"). For RAM it's caused by the number of address lines and the size of "row select" circuitry. For HDD it's caused by seek times. For humans getting the milk out of a refrigerator it's "search time + movement speed" (faster to get the milk out of a tiny bar fridge than to walk around inside a large industrial walk-in refrigerator).

However; there are special cases (there's always special cases). For example, you might have a computer that boots from network and then uses the network for persistent storage; where there's literally no secondary storage in the computer at all. Another special case is small embedded systems where RAM is often larger than persistent storage.