Type 1 VM - Machine > Hypervisor > Guest(s)
 [Xen]
 [VMware ESX server]
Type 2 VM - Machine > Host OS > VM > Guest(s)
 [VirtualBox]
 [VMware Workstation]

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Amazon EC2/Microsoft Cloud (Type 1)
- VM marketplace
- AWS = "Amazon Web Services"
Scaling under-utilized hardware (Type 1)
- Host WWW, Mail, DB, etc all together
Best of both worlds (Type 2)
- Best laptop (Macbook Pro)
- Worst software (Windows, cause you have to)
- Best software (Linux)
Testing X-platform/new kernels code (Type 2)
- Cheaper in expense
- " in setup
- Particularly in OS development
Run untrusted code (Type 2)
- Does it have a virus?
- Problematic if hardware intensive
- Link to trusted world is dangerous
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 Def 1 -  Sensitive inst: Behave different in user mode
 Def 2 - Privileged inst: It traps from user mode 
Prop 1 - Sensitive ⊆ Privileged
w/o this: inefficiency and/or binary rewriting

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