Flashcards
SCC 211 - Operating Systems - Memory Protection
Cards in this deck (14)
- 1What is the aim of Operating Systems?- You are trying to provide a platform, which a number of different processes can run concurrently.
- Aim to run multiple jobs
○ Each given share of computer resources - 2What is the functionality of Multi-programming?– Switches between processes as they
become blocked (waiting for I/O, etc)
□ Processes run, when they want to do something, they hand it over to the IO - 3What is the functionality of Multi-tasking (Sharing)?– Regularly switch between processes
so each appears interactive
□ OS forcibly takes control of machine and moves onto another process
□ It can be much more interactive - 4Why do each process has it's own base and limit in memory?Need to protect processes
from each other
Simple to set 2 registers in software - 5When addresses are dynamically changed within processes, explain the effects it has on the virtual and physical address?The process always sees addresses o to N within it's virtual address
Within a process physical address, it varies depending on where process is loaded in memory. - 6What are the 3 different types of dynamic storage allocation and define them?First fit - Always allocate first region of sufficient size found.
Best fit - Always allow smallest memory hole of sufficient size.
Worst fit - Always allocate largest memory hole (of sufficient size). - 7Problem with fragmentation in first and best fit schemes?Sum of un-allocated space can be large
– Requires complex de-fragmentation
• Shuffling memory contents
• Must be invisible to running processes - 8How does worst fit aim to reduce the problem of too large un-allocated space?- Leaves largest unallocated space
• Aims to increase chance of later allocation
(Note - It always tries to pick the largest amount of space) - 9What is external fragmentation?External fragmentation arises when free memory is separated into small blocks and is interspersed (scatter among or between other things) by allocated memory. It is a weakness of certain storage allocation algorithms, when they fail to order memory used by programs efficiently.
- 10What is internal fragmentation?Internal fragmentation is the wasted space within each allocated block because of rounding up from the actual requested allocation to the allocation granularity.
- 11Describe the variable/dynamic allocation scheme?- Allocate the request amount of memory
-External fragmentation (Space left outside/between allocated memory) - 12Describe the fixed size schemes?- Always allocate memory in fixed size blocks
-Internal fragmentation
Processes typically get more memory than requested (This will generally get unused). - 13Why is external fragmentation less of a problem than internal fragmentation????????
- 14What is paging?In computer operating systems, paging is a memory management scheme by which a computer stores and retrieves data from secondary storage for use in main memory. In this scheme, the operating system retrieves data from secondary storage in same-size blocks called pages.
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- Flashcards on SCC 211 - Operating Systems - Memory Protection, created by Ayo Olutobi on 25/01/2017.
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- Ayo Olutobi
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