1. Session 3 Memory Management
Hofstra University
Fall 2008
Session 3 Memory Management
Nassau Community College ITE153 – Operating Systems
Fall 2011 1
Network Security Course, CSC288 DL1

2. Hofstra University Memory In The Operating System
Session 3
Fall 2008
Memory In The Operating System
Nassau Community College ITE153 – Operating Systems
Fall 2011
Network Security Course, CSC288 DL1

3. What Is An Operating System (1)
Hofstra University
What Is An Operating System (1)
Fall 2008
A modern computer consists of:
One or more processors
Main memory
Disks
Printers
Various input/output devices
Managing all these components requires a layer of software – the operating system
Nassau Community College ITE153 – Operating Systems
Fall 2011
Network Security Course, CSC288 DL1

4. What Is An Operating System (2)
Hofstra University
What Is An Operating System (2)
Fall 2008
Nassau Community College ITE153 – Operating Systems
Fall 2011
Network Security Course, CSC288 DL1

5. Computer Hardware Review
Hofstra University
Computer Hardware Review
Fall 2008
Some of the components of a simple personal computer.
Nassau Community College ITE153 – Operating Systems
Fall 2011
Network Security Course, CSC288 DL1

6. Memory (1)
A typical memory hierarchy. The numbers are very rough approximations.
Nassau Community College ITE153 – Operating Systems
Fall 2011

7. Nassau Community College ITE153 – Operating Systems
Memory (2)
Questions when dealing with cache:
When to put a new item into the cache.
Which cache line to put the new item in.
Which item to remove from the cache when a slot is needed.
Where to put a newly evicted item in the larger memory.
Nassau Community College ITE153 – Operating Systems
Fall 2011

8. Hofstra University Memory Management
Session 3
Fall 2008
Memory Management
Nassau Community College ITE153 – Operating Systems
Fall 2011
Network Security Course, CSC288 DL1

9. Nassau Community College ITE153 – Operating Systems
No Memory Abstraction
Three simple ways of organizing memory with an operating system and one user process.
Nassau Community College ITE153 – Operating Systems
Fall 2011

10. Multiple Programs Without Memory Abstraction
Illustration of the relocation problem.
Nassau Community College ITE153 – Operating Systems
Fall 2011

11. Nassau Community College ITE153 – Operating Systems
Base and Limit Registers
Base and limit registers are used to give each process a separate address space.
Nassau Community College ITE153 – Operating Systems
Fall 2011

12. Nassau Community College ITE153 – Operating Systems
Swapping (1)
Memory allocation changes as processes come into memory and leave it. The shaded regions are unused memory.
Nassau Community College ITE153 – Operating Systems
Fall 2011

13. Nassau Community College ITE153 – Operating Systems
Swapping (2)
(a) Allocating space for growing data segment. (b) Allocating space for growing stack, growing data segment.
Nassau Community College ITE153 – Operating Systems
Fall 2011

14. Memory Management with Bitmaps
(a) A part of memory with five processes and three holes. The tick marks show the memory allocation units. The shaded regions (0 in the bitmap) are free. (b) The corresponding bitmap. (c) The same information as a list.
Nassau Community College ITE153 – Operating Systems
Fall 2011

15. Virtual Memory – Paging (1)
The position and function of the MMU – shown as being a part of the CPU chip (it commonly is nowadays). Logically it could be a separate chip, was in years gone by.
Nassau Community College ITE153 – Operating Systems
Fall 2011

16. Nassau Community College ITE153 – Operating Systems
Hofstra University
Computing Folklore
Fall 2008
Uncle Vito’s Motel
Nassau Community College ITE153 – Operating Systems
Fall 2011
Network Security Course, CSC288 DL1

17. Nassau Community College ITE153 – Operating Systems
Paging (2)
Relation between virtual addresses and physical memory addresses given by page table.
Nassau Community College ITE153 – Operating Systems
Fall 2011

18. Nassau Community College ITE153 – Operating Systems
Paging (3)
The internal operation of the MMU with 16 4-KB pages.
Nassau Community College ITE153 – Operating Systems
Fall 2011

19. Nassau Community College ITE153 – Operating Systems
Speeding Up Paging
Paging implementation issues:
The mapping from virtual address to physical address must be fast.
If the virtual address space is large, the page table will be large.
Nassau Community College ITE153 – Operating Systems
Fall 2011

20. Page Replacement Algorithms
Optimal page replacement algorithm
Not recently used page replacement
First-In, First-Out page replacement
Second chance page replacement
Clock page replacement
Least recently used page replacement
Working set page replacement
WSClock page replacement
Nassau Community College ITE153 – Operating Systems
Fall 2011

21. Working Set Page Replacement (1)
The working set is the set of pages used by the k most recent memory references. The function w(k, t) is the size of the working set at time t.
Nassau Community College ITE153 – Operating Systems
Fall 2011

22. Summary of Page Replacement Algorithms
Figure Page replacement algorithms discussed in the text.
Nassau Community College ITE153 – Operating Systems
Fall 2011

23. Separate Instruction and Data Spaces
(a) One address space. (b) Separate I and D spaces.
Nassau Community College ITE153 – Operating Systems
Fall 2011

24. Nassau Community College ITE153 – Operating Systems
Shared Pages
Two processes sharing the same program sharing its page table.
Nassau Community College ITE153 – Operating Systems
Fall 2011

25. Shared Libraries A shared library being used by two processes.
Nassau Community College ITE153 – Operating Systems
Fall 2011

26. Nassau Community College ITE153 – Operating Systems
Page Fault Handling (1)
The hardware traps to the kernel, saving the program counter on the stack.
An assembly code routine is started to save the general registers and other volatile information.
The operating system discovers that a page fault has occurred, and tries to discover which virtual page is needed.
Once the virtual address that caused the fault is known, the system checks to see if this address is valid and the protection consistent with the access
Nassau Community College ITE153 – Operating Systems
Fall 2011

27. Nassau Community College ITE153 – Operating Systems
Page Fault Handling (2)
If the page frame selected is dirty, the page is scheduled for transfer to the disk, and a context switch takes place.
When page frame is clean, operating system looks up the disk address where the needed page is, schedules a disk operation to bring it in.
When disk interrupt indicates page has arrived, page tables updated to reflect position, frame marked as being in normal state.
Nassau Community College ITE153 – Operating Systems
Fall 2011

28. Nassau Community College ITE153 – Operating Systems
Page Fault Handling (3)
Faulting instruction backed up to state it had when it began and program counter reset to point to that instruction.
Faulting process scheduled, operating system returns to the (assembly language) routine that called it.
This routine reloads registers and other state information and returns to user space to continue execution, as if no fault had occurred.
Nassau Community College ITE153 – Operating Systems
Fall 2011

29. Separation of Policy and Mechanism (1)
Memory management system is divided into
three parts:
A low-level MMU handler.
A page fault handler that is part of the kernel.
An external pager running in user space.
Nassau Community College ITE153 – Operating Systems
Fall 2011

30. Separation of Policy and Mechanism (2)
Page fault handling with an external pager.
Nassau Community College ITE153 – Operating Systems
Fall 2011

31. Nassau Community College ITE153 – Operating Systems
Segmentation (1)
A compiler has many tables that are built up as compilation proceeds, possibly including:
The source text being saved for the printed listing (on batch systems).
The symbol table – the names and attributes of variables.
The table containing integer, floating-point constants used.
The parse tree, the syntactic analysis of the program.
The stack used for procedure calls within the compiler.
Nassau Community College ITE153 – Operating Systems
Fall 2011

32. Nassau Community College ITE153 – Operating Systems
Segmentation (2)
In a one-dimensional address space with growing tables, one table may bump into another.
Nassau Community College ITE153 – Operating Systems
Fall 2011

33. Nassau Community College ITE153 – Operating Systems
Segmentation (3)
A segmented memory allows each table to grow or shrink independently of the other tables.
Nassau Community College ITE153 – Operating Systems
Fall 2011

34. Implementation of Pure Segmentation
Comparison of paging and segmentation.
Nassau Community College ITE153 – Operating Systems
Fall 2011

35. Segmentation with Paging: The Pentium (5)
Protection on the Pentium.
Nassau Community College ITE153 – Operating Systems
Fall 2011

36. <ALT><CTRL><DEL>
Hofstra University
<ALT><CTRL><DEL>
Fall 2008
Try <ALT><CTRL><DEL> to get into Task Manager
Nassau Community College ITE153 – Operating Systems
Fall 2011
Network Security Course, CSC288 DL1

37. Nassau Community College ITE153 – Operating Systems
Hofstra University
Fall 2008
Important URLs
Memory Management This is from the Microsoft point of view
Memory Management Linux Another point of view
Peter Denning Create Virtual Memory in 1970
Here are some useful URLs…
Nassau Community College ITE153 – Operating Systems
Fall 2011 37
Network Security Course, CSC288 DL1 37

38. Nassau Community College ITE153 – Operating Systems
Hofstra University
Homework
Fall 2008
Review the Slides
Keep Practicing Commands
Try <ALT><CTRL><DEL> to get into Task Manager
Read Section in the Text – Monitoring System Performance
Nassau Community College ITE153 – Operating Systems
Fall 2011
Network Security Course, CSC288 DL1