Bloomberg always have two codes for the same instruments. For example, for Apple, Bloomberg has AAPL US and AAPL UW.
I am wondering what is the difference between these two codes? As far as I can tell, if the stock is a US one, there will always be a code of the form "xxxx US".
So after working on the equity tech team for a year, now I have a much better understanding of it.
Bloomberg has two types of identifiers, one called Bloomberg Exchange Ticker, one called Bloomberg Composite Ticker. The Exchange vs. Composite is the pricing source concept mentioned by others.
The Bloomberg Exchange Ticker is relatively simpler to understand - it just stands for a security on a particular exchange. So if you go to Bloomberg terminal and ask it to give prices (last, bid, ask) for a Bloomberg Exchange Ticker (IBM UN for example), Bloomberg will give you the price only for that particular exchange (NYSE).
The Bloomberg Composite Ticker will combine prices from all possible exchanges and gives you an aggregated feed. For example, the last/bid/ask retrieved for IBM US will be:
- most recent last price happened on any exchange
- current highest bid on all exchanges
- current lowest ask on all exchanges
Usually the composite ticker will end with country code: IBM US, AAPL US, 1 HK etc. The Bloomberg exchange ticker will end with Bloomberg allocated exchange code: IBM UN (NYSE), AAPL UW (NASDAQ) etc.