[jQuery] difference between $.post and $.ajax

[jQuery] difference between $.post and $.ajax


I know there is a lot of difference, but what are the defaultsfor
$.post? I am asking this because I am able to send with this:
$.post( "/ajax", {"data" : json });
but not with this:
$.ajax({
type: "POST",
url: "/ajax",
data: json,
processData: false,
});
The first gives me an 200 back, the second an 500?
TIA
Ruediger