[概念學習] hypervisor

摘自wikipedia: http://en.wikipedia.org/wiki/Hypervisor

1. 定義：a piece of computer software, firmware or hardware that creates and runs virtual machines.
    別名：virtual machine manager (VMM)

2. 兩類hypervisor（按照是否直接運行在硬體上來區分）

• Type I: 直接運行在硬體上，如Citrix XenServer, VMware ESX/ESXi
• Type II: 運行在作業系統上，如KVM

3. paravirtualization
Guest operating-system to make system calls to the hypervisor, rather than executing machine I/O instructions that the hypervisor simulates.
paravirtualization是Xen裡的說法，其他產品對這個技術有不同的稱謂：a "hypercall" in Parallels Workstation, and a "DIAGNOSE code" in IBM's VM.