Hyper-V is a technology by Microsoft that allows you to run multiple OS on a single machine virtually i.e,you have one OS installed on which Hyper-V is running and through Hyper-V you are able to virtually break  your physical hardware into small fragments which will be capable of running a OS.This virtual hardware is known as virtual machine and the OS running on it act as normal OS we are used to.

Hyper-V requires a 64-bit system that has Second Level Address Translation (SLAT). SLAT is a feature present in the current generation of 64-bit processors by Intel & AMD. You’ll also need a 64-bit version of Windows 8, and at least 4GB of RAM. Hyper-V does support creation of both 32-bit and 64-bit operating systems in the VMs.

Hyper-V’s dynamic memory allows memory needed by the VM to be allocated and de-allocated dynamically (you specify a minimum and maximum) and share unused memory between VMs. You can run 3 or 4 VMs on a machine that has 4GB of RAM but you will need more RAM for 5 or more VMs.

You can also create large VMs with 32 processors and 512GB RAM.
As for user experience with VMs, Windows provides two mechanisms to peek into the Virtual Machine: the VM Console and the Remote Desktop Connection.

The VM Console (also known as VMConnect) is a console view of the VM. It provides a single monitor view of the VM with resolution up to 1600×1200 in 32-bit color. This console provides you with the ability to view the VM’s booting process.

For a richer experience, you can connect to the VM using the Remote Desktop Connection (RDC). With RDC, the VM takes advantage of capabilities present on your physical PC. For example, if you have multiple monitors, then the VM can show its graphics on all these monitors. Similarly, if you have a multipoint touch-enabled interface on your PC, then the VM can use this interface to give you a touch experience. The VM also has full multimedia capability by leveraging the physical system’s speakers and microphone. The Root OS (i.e. the main Windows OS that’s managing the VMs) can also share its clipboard and folders with the VMs. And finally, with RDC, you can also attach any USB device directly to the VM.

For storage, you can add multiple hard disks to the IDE or SCSI controllers available in the VM. You can use Virtual Hard Disks (.VHD or .VHDX files) or actual disks that you pass directly through to the virtual machine.

Hyper-V’s “Live Storage Move” capability helps your VMs to be fairly independent of the underlying storage. With this, you could move the VM’s storage from one local drive to another, to a USB stick, or to a remote file share without needing to stop your VM.

Another great feature of Hyper-V is the ability to take snapshots of a virtual machine while it is running. A snapshot saves everything about the virtual machine allowing you to go back to a previous point in time in the life of a VM, and is a great tool when trying to debug tricky problems.

Virtualization has its limitations. Features or applications that depend on specific hardware will not work well in a VM. For example, Windows BitLocker and Measured Boot, which rely on TPM (Trusted Platform Module), might not function properly in a VM, and games or applications that require processing with GPUs (without providing software fallback) might not work well either. Also, applications relying on sub 10ms timers, i.e. latency-sensitive high-precision apps such as live music mixing apps, etc. could have issues running in a VM.

Source : MSDN