An order book that only contains the basic components: sizes and prices. It is a simple electronic list of buy or sell orders of securities arranged as per price levels and time priorities. A trader with a higher price on the buy side or lower price on the sell side will be assigned priority over traders in terms of execution/ filling as per current, price level priorities. In case quoted prices are equal, priority will be decided as per timing of order placement: traders who are earlier in time will get the higher priority. Such order prioritization (order precedence rule and trade pricing rule) are usually used in all types of order-driven markets.

Order books are continuously updated- most often update takes place in real time during intraday trading.

For an example, see simple order book: an example.