▁hardware ▁level , ▁the ▁VM s ▁can ▁run ▁multiple ▁guest ▁OS es . ▁This ▁is ▁best ▁used ▁for ▁testing ▁and ▁training ▁that ▁require ▁networking ▁inter oper ability ▁between ▁more ▁than ▁one ▁OS es , ▁since ▁not ▁only ▁can ▁the ▁guest ▁OS es ▁be ▁different ▁from ▁the ▁host ▁OS , ▁there ▁can ▁be ▁as ▁many ▁guest ▁OS ▁as ▁VM s , ▁as ▁long ▁as ▁there ▁is ▁enough ▁CPU , ▁RAM ▁and ▁H DD ▁space . ▁IBM ▁introduced ▁this ▁around ▁ 1 9 9 0 ▁under ▁the ▁name ▁logical ▁partition ing ▁( LP AR ), ▁at ▁first ▁only ▁in ▁the ▁main frame ▁field . ▁ ▁At ▁the ▁operating ▁system ▁level , ▁it ▁can ▁only ▁virtual ize ▁one ▁OS : ▁the ▁guest ▁OS ▁is ▁the ▁host ▁OS . ▁This ▁is ▁similar ▁to ▁having ▁many ▁terminal ▁server ▁sessions ▁without ▁lock ing ▁down ▁the ▁desktop . ▁Thus , ▁this ▁is ▁the ▁best ▁of ▁both ▁world s , ▁having ▁the ▁speed ▁of ▁a ▁T S ▁session ▁with ▁the ▁benefit ▁of ▁full ▁access ▁to ▁the ▁desktop ▁as ▁a ▁virtual ▁machine , ▁where ▁the ▁user ▁can ▁still ▁control ▁the ▁quot as ▁for ▁CPU , ▁RAM ▁and ▁H DD . ▁Similar ▁to ▁the ▁hardware ▁level , ▁this ▁is ▁still ▁considered ▁a ▁Server ▁Virtual ization ▁where ▁each ▁guest ▁OS ▁has ▁its ▁own ▁IP ▁address , ▁so ▁it ▁can ▁be ▁used ▁for ▁networking ▁applications ▁such ▁as ▁web ▁hosting . ▁ ▁At ▁the ▁application ▁level , ▁it ▁is ▁running ▁on ▁the ▁Host ▁OS ▁directly , ▁without ▁any ▁guest ▁OS , ▁which ▁can ▁be ▁in ▁a