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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 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 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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