ON STAR ARR WITH RADAR VECTORS; ATC ADVISED FLC THAT THEY SHOULD HAVE SLOWED TO 200 KTS BECAUSE THEY WERE BELOW CLASS B AIRSPACE. NORMALLY; ATC ADVISES OF SPD RESTRS; BUT IF THEY DON'T; IT IS STILL FLC RESPONSIBILITY TO COMPLY WITH APPLICABLE RESTRS.

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WE WERE ON THE AWSON 8 ARR INTO PDK; JUST PAST TEGRE INTXN AT 8000 FT (ALT ON STAR AS 'EXPECT'). TEGRE IS 45 DME FROM ATL VOR. ATL APCH GAVE TURN TO HDG 190 DEGS; DSND TO 4000 FT FOR VECTORS FOR VISUAL RWY 2R PDK. WE TURNED TO 190 DEGS AND BEGAN NORMAL DSCNT TO 4000 FT. BEFORE REACHING 4000 FT; APCH GAVE TURN TO 200 DEGS AND ADVISED OUR AIRSPD SHOULD BE 200 KTS OR LESS. CAPT ACKNOWLEDGED TURN TO 200 DEGS AND ADVISED APCH WE WERE NOT GIVEN EARLIER SPD RESTR. APCH THEN ADVISED US SPD RESTR IS REG BELOW CLASS B AIRSPACE. WE IMMEDIATELY SLOWED ACFT TO BELOW 200 KTS. THE FARS CLRLY HOLD THE PLT FULLY RESPONSIBLE FOR POS AWARENESS AND COMPLIANCE WITH ALL AIRSPD RESTRS; CHARTED OR UNCHARTED. HOWEVER; WHEN ON RADAR VECTORS FROM A STAR; IT CAN BE VERY DIFFICULT TO DETERMINE YOUR POSITION IN RELATION TO CLASS B AIRSPACE. IFR CHARTS ONLY DEPICT THE GENERAL POS OF THE AIRSPACES; WHICH USUALLY HAVE IRREGULAR SHAPES AND COMPLICATED ALTS. I UNDERSTAND THE IMPORTANCE OF OBSERVING AIRSPD RESTRS; BUT ALSO REALIZE IT IS IMPORTANT TO ASSIST ATC IN MAINTAINING THE SAFE FLOW OF TFC. USUALLY ATC DOESN'T EXPECT YOU TO MAKE LARGE SPD REDUCTIONS UNTIL NECESSARY (IE; JUST PRIOR TO ENTERING THE AIRSPACE BELOW THE CLASS B). IN ORDER TO AID PLTS IN DETERMINING WHEN AN AIRSPD ADJUSTMENT IS REQUIRED; I SUGGEST NOTATIONS BE MADE ON STARS IF THEY HAVE ALTS THAT MAY BRING YOU IN BELOW THE CLASS B. ATL CLASS B IS A PARTICULARLY BAD ONE FOR THIS SINCE THE FLOORS ARE SO HIGH (10000 FT; 8000 FT; 6000 FT) COMPARED TO OTHER CLASS B'S (FOR EXAMPLE NEW YORK). PERHAPS THE FLOORS OF THE ATL CLASS B NEED TO BE LOWERED. ALSO; I'M REMINDED; ONCE AGAIN; NOT TO ASSUME ANYTHING IN AVIATION. I ALWAYS EXPECTED THAT IFR TURBOPROP/TURBOJET TFC IS KEPT INSIDE CLASS B AIRSPACE THROUGH DSCNT TO THE ARPT. I UNDERSTOOD THAT THE PURPOSE OF CLASS B AND ITS SHAPE (GENERALLY; UPSIDE-DOWN WEDDING CAKE) WAS TO KEEP THE SAFE AND EXPEDITIOUS FLOW OF AIR TFC. HOWEVER; THAT IS NOT THE CASE IF GOING INTO AN ARPT OTHER THAN THE PRIMARY ARPT. THAT IS DEFINITELY SOMETHING I WILL WATCH OUT FOR IN THE FUTURE!