1. Rehearsals on Operating systems RAM and traditional memory in a computer Source: Partly from Per S. Laursen

2. EASJ - Partly from Per's slides2 Internal memory What is internal memory anyway? Just some chips that hold a certain amount of data In a modern computers the internal memory typically consist of 2-16 Gigabyte What kind of data is stored? E.g. music on a mp3 file, that the CPU has to compute to turn it into music.

3. EASJ - Partly from Per's slides3 Internal vs. external RAM as a kind of Internal storage has one big advantage: transfer of data between the CPU and RAM is pretty fast (several Gigabytes per. Seconds) Fast yes, - but compared to what? But there are some major drawbacks: – RAM is pretty expensive (compared to what?) – When power is turned off, all data disappear from the internal storage – We therefore also need an external storage

4. EASJ - Partly from Per's slides4 The external memory/storage Where does the data in the internal memory comes from? The data comes from the external storage What is the external storage? Overall, the same as the internal storage, ie a passive storage of data, BUT – Is usually much cheaper than RAM – Retains data when power is turned off Most common form of external storage in a modern PC is a hard drive

5. EASJ - Partly from Per's slides5 A hard item… Moderne harddiske rummer typisk 200-1000 Gigabyte A hard disk drive includes a number of magnetic plates, where bits are stored, by magnetising a certain region of the plate Modern hard drives typically houses 300-4000 Gigabyte

6. EASJ - Partly from Per's slides6 Harddrive vs. RAM HarddriveRAM Typical amount in a PC 200-1000 GB4-16 GB Price per Gigabyte0,50-1 kr.50-200 kr. Transfer rate0,1-0,3 GB/sec4-8 GB/sec Saves data without electricity YesNo TechnologyMechanicalElectronically

7. EASJ - Partly from Per's slides7 Harddrive vs. RAM In other words: RAM: – Very fast and stable, but – Very expensive, and does not save data without power/electricity. Harddrive: – Very cheap and has a big capacity, and saves data without power/electricity, but – Very slowly, and is based on technic

8. Hard drive vs Solid State drive New: SSD (Solid State Drive). Faster than Hard drive. But more expensive than Hard drive.

9. EASJ - Partly from Per's slides9 Harddrive vs. SSD HarddriveSSD Typical amount in a PC 200-1000 GB64-256 GB Price per Gigabyte0,50-1 kr.7-12 kr. Transfer rate0,1-0,3 GB/sec4,8 - 6 GB/sec (SATA 3/6) Saves data without electricity Yes TechnologyMechanicalElectronically

10. EASJ - Partly from Per's slides10 Is a computer ”born” with an Operating system (OS)? BIOS handles very basic actions as a keystroke, and the drawing of letters on the screen When a computer starts, the BIOS is set to start The main task of the BIOS is starting the right operating system BIOS is a chip in your PC

11. EASJ - Partly from Per's slides11 Administration of programs Last time we discussed what it means, when the virtual memory is larger than the RAM. When we start a program, it will be copied from the external memory/storage to the internal storage(RAM), and set in motion Operating system Program The internal storage (RAM)

12. EASJ - Partly from Per's slides12 Administration of programs The operating system must "find room" for the program in the internal storage - what if there is no more space? Internal storage Program What now?

13. EASJ - Partly from Per's slides13 Administration of programs The operating system can use some of the external storage (hard drive), as an "emergency extension" to the internal storage Internal storage Program Additional (temporarily) internal storage Program