Windows defender and Microsoft security essentials?

Two different products:
Quoted from Microsoft web page;

[ What's the difference between Microsoft Security Essentials and Windows Defender?

Microsoft Security Essentials is antimalware software, which means that it's designed to detect and help protect your PC against a wide range of malicious software, including viruses, spyware, and other potentially unwanted software. Windows Defender, which is automatically installed with your Windows operating system, is software that detects and stops spyware. ]

Windows Defender is automatically (or should be) disabled when another anti-virus is installed. If MSE has been working fine for you, then you have more luck then most do as its ratings are poor.

You can't run to anti virus programs glad you turned off defender, but i wish you would consider changing to another form of protection than MSE like already posted has very poor ratings. Avira is very good and avast

Microsoft Security Essentials has a self-contained anti-virus program in it. It may even be Windows Defender in a modified form and you would not want 2 instances of that running simultaneously.

As far as to which is better, MSE is more comprehensive and therefore takes more of your machine's resources. Though Microsoft claims that it is lightweight, I have found it using 35-40 percent of the CPU at inconvenient times. Windows Defender is just another virus checking program in the sea of virus checking programs.

I personally just use Windows Defender occasionally in scan mode. If you leave real time mode on and just bring up a folder with a bunch of programs listed in Windows Explorer, it goes crazy and tries to scan everything. And it makes your boot time significantly longer. MSE makes that even longer.