When is the Journal of the ACM issued?
Judging from their archive, it seems that since 1994 the Journal of the ACM is issued 6 times a year, so roughly every other month. Until 2006 it was published on odd months. From 2007 on, the schedule seems to be somewhat random, but there are still 6 issues a year (though sometimes one of them is published on the wrong year, as in 2009 and 2010).