The US Nasdaq electronic stock market plans to invest $100m to replace its computerised trading system with new hardware and software to boost the volume of trades that can be processed, cut operating costs and make it easier to introduce new trading products and dealing systems to the market; once the work is finished, Nasdaq says it will be able to handle up to 800m shares a day, double the current 400m capacity; Nasdaq handled its highest volume in mid-January when trading hit 328m shares a day; it will also replace its mainframes in Trumbull, Connecticut and Rockville, Maryland from 1994 to 1997; no word on what the mainframes are.