simple question trading

Most BB trading is not actual prop trading (what you described) and is actually market making--taking orders from clients and being on either side of the trade, essentially providing liquidity to clients and making money off of the bid/ask spread. Obviously there is a certain amount of prop inherent to this, but much of that will potentially be going away if the Volcker Rule ever gets put into place (most banks have done away with all of their pure prop desks). Generally speaking, trading is significantly more short term than AM, and trades are done on a MUCH more frequent basis. AM also tries to make money for their investors, whereas traders simply make markets for their clients and provide liquidity, thus allowing them to trade whatever security in whatever amount. There is much more to it but that's a basic overview. also, AM=buy side BB S&T=sell side.