2. ICC Module 3 Lesson 2 – Memory Hierarchies 1 / 6 © 2015 Ph. Janson Information, Computing & Communication Memory Hierarchies – Clip 2 – Concept School of Computer Science & Communications B. Falsafi (charts), Ph. Janson (commentary)

3. ICC Module 3 Lesson 2 – Memory Hierarchies 2 / 6 © 2015 Ph. Janson Outline ►Clip 1 – TechnologiesClip 1 ►Clip 2 – ConceptClip 2 ►Clip 3 – PrincipleClip 3 ►Clip 4 – ImplementationClip 4 ►Clip 5 – Reading memoryClip 5 ►Clip 6 – Writing memoryClip 6 ►Clip 7 – Cache management – the Least Recently Used algorithmClip 7 ►Clip 8 – A simulated exampleClip 8 ►Clip 9 – LocalityClip 9 First clipPrevious clipNext clip

4. ICC Module 3 Lesson 2 – Memory Hierarchies 3 / 6 © 2015 Ph. Janson Problem ! RAM is the only media whose throughput and latency match processor performance BUT it presents a prohibitive cost and thus a limited size not to mention that it forgets everything when it is powered off ! Performance RAM Flash Magnetic tape Capacity Disk

5. ICC Module 3 Lesson 2 – Memory Hierarchies 4 / 6 © 2015 Ph. Janson Solution: hierarchical memory Keeping in fast memory only what is currently in use Proc FLASH Storage Memory Information in use managed automatically (user / program not involved) Transient Informations archived managed “manually” (by user or program) Perennial On-chip memory Off-chip memory Hard disk Magnetic tape Next lesson This lesson

6. ICC Module 3 Lesson 2 – Memory Hierarchies 5 / 6 © 2015 Ph. Janson A real life analogy Clothes in a suitcase Limited space Temporary usage For a trip Depending on climate Assorted colors Carry with you …but in your cupboard All your clothes Permanently Only at home

7. ICC Module 3 Lesson 2 – Memory Hierarchies 6 / 6 © 2015 Ph. Janson Another real life analogy Music / photos on your smartphone Limited space Temporary use Close, in your pocket … but on your laptop “Unlimited” capacity All your songs/photos/films Distant, at home