My workout looks something like this:
Day 1: Legs
Day 2: chest/shoulders (front, side delts)
Day 3: back/traps (rear delts)
Day 4: arms
I insert rest days where needed, and typically work out 4 times in 6 days... rest days often involve cardio and abs... plus I typically train abs at the end of every other workout
Training interval is something less than 1x per week (1 training session per body part, every 6 days). When I start training heavy legs again, I may split out hams from quads as my lower back cannot take that much punishment in a single day.
Adding in a day dedicated to arms basically means they get trained 2x (once on arm day, again on chest or back day) every 6 days... and I have been very pleased with progress to date.
If I am recovering, then less rest days - if not, then a few more... but, this is just what works for me. Lotta good programs described in previous posts.