Dividing hardware resources of many computers and virtualizing them as one computer is called Logical Partition or LPAR
. It seen that mostly logical partition is done on hardware. You can divide a single machine into several parts and each one of them can be loaded with separate operating system. One partition can control memory of the second partition by commanding a process on the second partition to directly operating on the memory. Two different LPARs can access memory from a single common chip, but only with a range of addresses and they should be directly accessible and do not overlap each other. CPU can either be dedicated to one partition or can be shared between two. First company to use LPAR technology was IBM in early 80s. it was developed for mainframe architecture ESA/390. PR/SM facility manages LPARs on IBM mainframes. There are few modern IBM mainframes operate exclusively in LPAR mode, irrespective of the fact that there is only single logical partition on a machine. Using Logical Partition has many advantages, like easy to use, little costs and fast working. IBM mainframe LPARs are even secure to be used by highest security organizations like military. Reason behind this is that IBM mainframe LPARs are Common Criteria Certifiable i.e. they work as completely physical separate servers. Talking about IBM mainframes nearly all of them run with multiple LPARs with IBM System z10 and IBM System z9. They support almost 60 LPARs. LPARs are compatible with multiple operating systems like AIX, i5/OS, Linux, z/OS.