How light mode maintains memory time product

Question

How does exactly light mode in RX maintains memory time product.

Answer 1

Full mode (fast) is fast because the full dataset is generated up-front, i.e. the full ~2G dataset is generated, in memory, beforehand.

Light mode (slow) is slow because the dataset items will be generated on the fly (as they are needed).

When mining, you want to create hashes as fast as possible. You'll be changing the message (the input being hashed, e.g. changing the nonce), but don't want to be creating dataset items on the fly, because this will slow you down. Hence light mode is useless for mining (it runs much slower because it has to generate dataset items on the go), but useful for verification only purposes (where absolute speed is of less importance).