Memory Management. Memory Management. Chapter 11. Memory Management Techniques. I. Single Contiguous. II. Overlays. Advantages: Disadvantages:

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1 Chptr 11 Mmory Mngmnt Mmory Mngmnt Min mmory is rsour tht must llot n llot Min Mmory OS CPU Mmory Mngmnt Thniqus trmin: Whr n how pross rsis in mmory How rssing is prform ining: intifirs --> ompil rltiv rsss (rltiv to 0) --> physil rsss Mmory Mngmnt Thniqus I. Singl Contiguous 1)Singl Contiguous 5) Pging 2)Ovrlys 6) Dmn Pging 3)Fix (Stti) Prtitions 7) Sgmnt 4)Rlotion (Dynmi) Prtitions 8) Sgmnt / Dmn Pging For h thniqu, osrv: lgorithms vntgs / Disvntgs Spil Rquirmnts Whil (( jo jo is is ry )) Do Do If If (( JoSiz <= <= MmorySiz )) Thn gin llot Mmory Lo n n Exut Jo Jo Dllot Mmory En En Els Error I. Singl Contiguous vntgs: Simpliity No spil hrwr Disvntgs: CPU wst Min mmory not fully us Limit jo siz II. Ovrlys Progrms n stion into mouls Not ll mouls n to in min mmory t th sm tim C D Progrmmr spifis whih mouls n ovrly h othr Linkr insrts ommns to invok th lor whn th mouls r rfrn Th "prnt" must sty in mmory Us in DOS s n ltrntiv to Expn Mmory. E

2 Illustrtion of Ovrlys Progrm Componnt: C D E Mmory: 40K 30K 10K 10K 40K Ovrlys vntgs: Ru mmory rquirmnts Without Ovrlys C D E C D With Ovrlys E Disvntgs: Ovrlp mp must spifi y progrmmr Progrmmr must know mmory rquirmnts Ovrlpp mouls must ompltly isjoint Fix (Stti) Prtitioning with solut Trnsltion Erlist ttmpt t multiprogrmming Prtition mmory into fix siz rs: 0M 16M Prtition #1 Prtition #2 Prtition #3 6M 2M 8M Fix (Stti) Prtitioning with solut Trnsltion Eh prtition n hol ONE pross Co gnrt using n SOLUTE rss rflting th strting rss of th prtition in whih it is suppos to xut (rltiv to 0, 6M, or 8M in pitur) Quu of prosss witing for h prtition Fix (Stti) Prtitioning with solut Trnsltion Fix (Stti) Prtitioning with solut Trnsltion

3 Frgmnttion- Dfinitions Fix Prtition Frgmnttion Frgmnttion is sitution in whih th fr lls in min mmory r not ontiguous. Prtition = IN USE = Jo Siz 20K 20K Intrnl frgmnttion: sitution in whih fr mmory lls r within th r llot to pross 35K 25K 10 K 10K Extrnl frgmnttion: 30K 30 K 30K sitution in whih fr mmory lls r not in th r llot to ny pross Extrnl frgmnttion: 35K prtition Intrnl frgmnttion: => 15K wst insi 25K prtition Fix Prtitioning with solut Trnsltion: Pros/Cons Fix Prtitioning with solut Trnsltion: Pros/Cons Disvntgs: vntgs: Simpliity Multiprogrmming now possil Works with ny hrwr (8088, 68000, t) Jo Siz <= Mx Prtition Siz <= MM Siz Storg wst u to intrnl frgmnttion: pross siz < prtition siz Storg wst u to xtrnl frgmnttion: prtition my il us non of th jos ssign to it r ing run On ompil jo n only xut in signt prtition Fix (Stti) Prtitions with Rltiv rss Trnsltion Fix Prtitions with Rltiv rss Trnsltion Illustrtion: - llows pross to run in ny fr prtition - LL Co gnrt using rsss rltiv to zro Lt: not s (solut) rss of prtition L not prtition lngth s Rg + L Prtition + Virtul rss QTP: Woul Pointrs work?

4 Multiprogrmming Prottion Multiprogrmming Prottion Fix prtitions with rltiv rssing supports multiprogrmming prottion => Ensur tht on pross os not ss mmory sp it to nothr pross Mtho: Eh rltiv rss is ompr to th ouns rgistr + L Prtition OK T < s Rg + Virtul rss ouns Rg +L F Error: Illgl rss Fix Prtitioning with Rltiv rssing: Pros/Cons vntg ompr to solut rssing: IV. Dynmi Prtitions Consir following snrio (100K mmory): Dynmi llotion of progrms to prtitions improvs systm prformn Still som isvntgs: Prtition sizs r fix t oot tim Cn't run pross lrgr thn lrgst prtition Prtition sltion lgorithm ffts systm prformn Still hs intrnl n xtrnl frgmnttion Jo Jo 1 rrivs; siz= K Jo Jo 2 rrivs; siz= K Jo Jo 3 rrivs; siz= K Jo Jo 4 rrivs; siz=10 K Jo Jo 1 trmints Jo Jo 3 trmints Jo Jo 5 rrivs; siz=12k Whr shoul jo 5 put? Prtition Sltion lgorithms Implmnttion rquirs fr lok tl Sorting tl in prtiulr mnnr rsults in spifi sltion lgorithm: 1) First Fit -- Tl sort y lotion, srh top to ottom 2) st Fit -- Tl Sort y siz (sning) [on't rk up ig loks] 3) Worst Fit -- Tl sort y siz (sning) [rk up ig loks] 4) Nxt Fit Whr os Jo 5 Go? First Fit Jo Jo 5 rrivs; siz=12k Fr List Tl - First Fit Strt r Lngth

5 Whr os Jo 5 Go? st Fit Whr os Jo 5 Go? Worst Fit Fr List Tl - st Fit Strt r Lngth Fr List Tl - Worst Fit Strt r Lngth Jo Jo 5 rrivs; siz=12k Jo Jo 5 rrivs; siz=12k Whr os Jo 5 Go? Nxt Fit Fr List Tl - Nxt fit Strt r Lngth Dynmi Prtitions Rquirs two OS oprtions: llotion: Form prtition from fr prtition of mpl siz Dllotion: Rturn prtition to fr tl n mrg whr possil Jo Jo 5 rrivs; siz=12k In us llot fr Mrg Exmpl Mrg Exmpl Suppos oms fr IN USE - 24 K IN USE - 10 K Fr List Tl - First Fit Strt r Lngth Suppos oms fr IN USE - 24 K IN USE - 10 K Fr List Tl - st Fit Strt r Lngth Wht os Fr List Tl look lik? Wht os Fr List Tl look lik?

6 Mrg Exmpl Mrg Exmpl Suppos oms fr Fr List Tl - Worst Fit Suppos oms fr Fr List Tl - Nxt fit Strt r Lngth Strt r Lngth IN USE - 24 K IN USE - 24 K IN USE - 10 K IN USE - 10 K Wht os Fr List Tl look lik? Wht os Fr List Tl look lik? Wht if w nnot fin ig nough hol for n rriving jo? Comption Shuffl jos jos to to rt lrgr ontiguous fr fr mmory Suppos 35K jo rrivs? Suppos 90K jo rrivs? Jo 15 K 15K 20K Fr 22 K Jo 20 K C 7K Wht o you o? Fr 2 4 Fr 24 K 30 K 10 K 14 K Jo C 7K Now 40 K jo n run 58K QTP: How out pointrs? Pros/Cons of Dynmi Prtitions vntgs: Effiint mmory usg Disvntgs: Prtition Mngmnt Comption or xtrnl frgmnttion Intrnl frgmnttion (if loks omposing prtions r r lwys llot in fix siz units --.g. 2k) Multipl Sgmnt Rlotion rgistrs CPU (Gnrt rss) Rltiv rss Co Rgistr Stk rgistr + Dt Rgistr Mmory rss Rgistr Primry Mmory