Why Does Your Computer Need RAM When It Has an SSD?

Every laptop lists two numbers in gigabytes: a big one for the SSD and a small one for RAM. Both hold your computer's data. So why does it need the small one at all? This video shows what would happen if your computer had to work straight from its SSD. Chapters 0:00 Two numbers on every laptop 0:27 Storage and memory 1:11 A workday without memory 2:03 One big request, or many small ones 2:54 Why storage is hard to change 3:29 Why memory forgets 4:23 When memory is full 5:13 The answer Sources Arpaci-Dusseau & Arpaci-Dusseau, Operating Systems: Three Easy Pieces, chapters on flash-based SSDs, swapping and processes: https://pages.cs.wisc.edu/~remzi/OSTEP/ Matthews, Newhall & Webb, Dive Into Systems, chapter 11 (storage and the memory hierarchy): https://diveintosystems.org/book/C11-MemHierarchy/ Samsung, NVMe SSD 990 PRO datasheet: https://download.semiconductor.samsung.com/resources/data-sheet/Samsung_NVMe_SSD_990_PRO_Datasheet_Rev.1.0_10129514072296.pdf Nair, Chou & Qureshi, A Case for Refresh Pausing in DRAM Memory Systems (HPCA 2013): https://fast.cc.gatech.edu/papers/HPCA_2013_1.pdf Cai et al., Error Characterization, Mitigation, and Recovery in Flash-Memory-Based Solid-State Drives (Proceedings of the IEEE, 2017): https://arxiv.org/abs/1706.08642 Halderman et al., Lest We Remember: Cold Boot Attacks on Encryption Keys (USENIX Security 2008): https://www.usenix.org/legacy/event/sec08/tech/full_papers/halderman/halderman.pdf Simplified: the times are round numbers for one fast SSD and for typical memory, and the "one step" scale is rough. The distance on screen is not to scale, and the pile of coins only means "costs more", not a real price ratio. The processor's own small, even faster memory (the cache) is left out; that is a video of its own.