Virtual Machine

• A virtual machine is a software computer that like a physical computer, runs on operating system and application. 
• Every virtual machine has virtual devices that provide the same functionality as physical hardware.
• A virtual machine consists of several types of files that you store on a supported storage device. 
• The key files that make up a virtual machine are the configuration file, virtual disk file, NVRAM setting file, and the log file.

File Extension	Description
.vmx	VM configuration file
.vmxf	Addtional VM configuration file          or Internal metadata file details
.vmdk	Virtual disk descriptor and VM metadata
Flat.vmdk	VM’s data virtual disk file (OS/Application
.nvram	VM BIOS (or) EFI configuration (Extensible firmware interface)
.vmsd	Snapshot manager file (or) VM snapshot
.vmsn	Snapshot memory file, VM snapshot data file
.vswp	VM swap file
.vmss	VM suspend file
.log	Current VM log file
#.log	Old VM log file
.rdm	RDM file with virtual compatibility
.rdmp	RDM file with physical compatibility

Three types of virtual disk

1. Thick Provision Lazy Zeroed
2. Thick Provision Eager zeroed
3. Thin Provision

Memory overhead.

• Overhead memory includes space reserved for the virtual machine frame buffer and various virtualization data structures, such as shadow page tables. 
• Overhead memory depends on the number of virtual CPUs and the configured memory for the guest operating system. 
• Virtual machines incur overhead memory. You should be aware of the amount of this overhead.

The following table lists the amount of overhead memory a virtual machine

Ballooning drivers
 Memory hock

10 VM x 10GB = 100 GB
10 VM x 4GB = 40 GB
                          _______
                            140GB
                          ________ Storage required