CST 334 Week 4 Learning Journal

This week we continued learning about memory virtualization and the different types of ways operating systems virtualize memory. Segmentation is a way that chops things up in to variable sized pieces but because of this it can lead to fragmentation which causes allocation to become more challenging. Another approach would be to chop up the space into variable sized pieces, called paging. Paging divides pieces up into pages (instead of code heap, or stacks). Paging views memory as an array of fixed size slots called page frames. Each of these two has their own challenges and advantages. To record where pages are stored In the physical memory, a page table is used and it stores address translations of the pages. 

There is also the hybrid approach. Which Is a combination of paging and segmentation. Thrashing can also occur when paging because the memory is overused, and the demands of the running processes exceeds the available physical memory. This leads to the system constantly paging and degrading performance. The admission control process and working sets (which are the pages that are being actively used) are also some things I learned this week. 

We also learned about translation-lookaside buffer (TLB) which is a part of the chips memory-management unit (MMU). A TLB is a hardware cache of virtual to physical address translations. On each memory reference, the hardware checks the TLB to see if the translation is held and if it is then the translation is performed quickly. 

There are many ways operating systems virtualize memory which we learned about this week and a lot more knowledge gained about operating systems.