As per this response, the complete steps are:
1) Open SDK Manager (In Android Studio, go to Tools > Android > SDK Manager) and Download Intel x86 Emulator Accelerator (HAXM installer) if you haven’t.
2) Now go to your SDK directory C:users%USERNAME%AppDataLocalAndroidsdkextrasintelHardware_Accelerated_Execution_Manager and run the file named intelhaxm-android.exe.
In case you get an error like “Intel virtualization technology (vt,vt-x) is not enabled”. Go to your BIOS settings and enable Hardware Virtualization.
3) Restart Android Studio and then try to start the AVD again.
It might take a minute or 2 to show the emulator window.
[edit]
The Android developer page has been updated with an excellent guide to get an emulator up and running.
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Install the Intel x86 Emulator Accelerator using the Android SDK Manager
If you have Android Studio installed, you can start the SDK manager via Tools -> Android -> SDK Manager.
The Android SDK Manager does not actually install HAXM, it just downloads it. In the top of the Android SDK manager window, you can find where the installer is located on your PC. Please open the subfolder extrasintelHardware_Accelerated_Execution_Manager, and run the installer manually: intelhaxm-android.exe.
To use the intel HAXM, you need to have a CPU with virtualization support:
Before attempting to use this type of acceleration, you should first
determine if your development system’s CPU supports one of the
following virtualization extensions technologies:
Intel Virtualization Technology (VT, VT-x, vmx) extensions
AMD Virtualization (AMD-V, SVM) extensions (only supported for Linux)
[edit]
As of Nov 27, 2019, Google has released an emulator for AMD CPUs.
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If your CPU does not have virtualization support, you could use an ARM emulator instead:
You can edit an existing, or add a new Virtual Device in the Android
Virtual device Manager, and change CPU/ABI to ARM.
If that option is not available, you may need to change the target API of the Virtual Device, or download an
ARM system image for the API version you want using the Android SDK
manager.