Csc 350 operating systems
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CSC 350 - Operating Systems. CSC 350 - Operating Systems. CSC 350 - Operating Systems. Creeds or Chaos?. Memory Management I. II. Memory Management I. manage the scarce resource of memory. Memory Management I. C. Dynamic partitions MMS. Partitions are created dynamically “on the fly”.

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CSC 350 - Operating Systems

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Csc 350 operating systems

CSC 350 - Operating Systems


Csc 350 operating systems1

CSC 350 - Operating Systems


Csc 350 operating systems2

CSC 350 - Operating Systems

  • Creeds or Chaos?


Memory management i

Memory Management I

II. Memory Management I

  • manage the scarce resource of memory


Memory management i1

Memory Management I

C. Dynamic partitions MMS

  • Partitions are created dynamically “on the fly”


Memory management i2

Memory Management I

3. OS concept - allocation

  • programs must be assigned to memory

  • note: if not enough contiguous RAM, program must wait


Memory management i3

Memory Management I

  • programs must be assigned to memory

  • how? (tradeoffs)


Memory management i4

Memory Management I

a. first-fit

  • the first (lowest) partition big enough for the program will be allocated


Memory management i5

Memory Management I

a. first-fit

  • adv: fast allocation


Memory management i6

Memory Management I

b. best-fit

  • the best (causing least fragmentation) partition will be allocated


Memory management i7

Memory Management I

b. best-fit

  • adv: best utilization


Memory management i8

Memory Management I

3. OS concept - allocation

  • tables 2.2 and 2.3


Memory management i9

Memory Management I

3. OS concept - allocation

  • suitcase analogy


Memory management i10

Memory Management I

3. OS concept - allocation

example problem 4, p.39

  • Job / Program size

  • Block / Partition size


Memory management i11

Memory Management I

Memory “map”

Jobs = programs on storage

block 1

block 2

block 3

610K

850K

J1 = 740K

J2 = 500K

J3 = 700K

700K


Memory management i12

Memory Management I

Memory “map”

a. best fit

block 1

block 2

block 3

J2 = 500K

610K

J1 = 740K

850K

J3 = 700K

700K


Memory management i13

Memory Management I

Memory “map”

b. first fit

low - highsearch

block 1

block 2

block 3

J2 = 500K

610K

J1 = 740K

850K

J3 = 700K

700K


Memory management i14

Memory Management I

Memory “map”

b. first fit

high-low search

block 1

block 2

block 3

610K

J1 = 740K

850K

J2 = 500K

700K

J3 = 700K wait


Memory management i15

Memory Management I

3. OS concept - allocation

  • group exercise :-)modified problem 4, p.39


Memory management i16

Memory Management I

  • modified problem 4, p.39

  • Job Size Block Size

  • 1 740K 1 610K

  • 2 500K 2 850K

  • 3 600K 3 500K


Memory management i17

Memory Management I

3. OS concept - allocation

  • anotheranalogy


Memory management i18

Memory Management I

4. OS - deallocation

  • programs must be removed from memory when finished


Memory management i19

Memory Management I

4. OS - deallocation

easy for fixed partitions

  • more difficult for dynamic partitions


Memory management i20

Memory Management I

scenarios:

  • a. deallocated memory is not adjacent to free memory


Memory management i21

Memory Management I

  • a. deallocated memory is not adjacent to free memory

allocated

To be deallocated

allocated


Memory management i22

Memory Management I

4. OS - deallocation

  • scenarios:

  • b. deallocated memory is adjacent to one free memory partition


Memory management i23

Memory Management I

  • b. deallocated memory is adjacent to one free memory

free

To be deallocated

allocated


Memory management i24

Memory Management I

4. OS - deallocation

  • scenarios:

  • c. deallocated memory is between two free memory partitions


Memory management i25

Memory Management I

  • c. deallocated memory is between two free memory blocks

free

To be deallocated

free


Memory management i26

Memory Management I

D. Relocatable Dynamic partitions MMS

  • 1. Based upon Dynamic Partitions MMS with additional feature


Memory management i27

Memory Management I

Based upon Dynamic Partitions MMS with additional feature

  • At times, OS will “compact” memory


Memory management i28

Memory Management I

Red = allocated partitions

Green = free space (unallocated RAM)


Memory management i29

Memory Management I


Memory management i30

Memory Management I

2. Tradeoffs

  • a. advantages

  • b. disadvantages


Memory management i31

Memory Management I

review CS:AO sections 2.2 and 2.3


Memory management i32

Memory Management I

3. OS needs h/w assistance

  • bounds register

  • relocation register


Memory management i33

Memory Management I

B1 = 20K

B2 = 10K

B3 = 30K

Prog K

Prog B

Prog S

now,

Program B terminates,


Memory management i34

Memory Management I

B1 = 20K

B2 = 10K

B3 = 30K

Prog K

Prog S

now,

Program Bterminates,OS deallocates Partition 2


Memory management i35

Memory Management I

B1 = 20K

B2 = 30K

Prog K

Prog S

now,

Program Bterminates,OS deallocates Partition 2 and compacts (relocates)


Memory management i36

Memory Management I

B1 = 20K

B2 = 30K

Prog K

Prog S

Prog S

Bounds Register = 30K

Relocation Register = -10K


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