Where do online stock brokers get their real-time data from?
Generally Google gets their data,  directly from the exchanges (Nasdaq, NYSE). This is really expensive   -- tens of thousands of dollars a month just for the license from the exchange, and lots of telecom costs on top of that. As another answer started, this information comes straight from an exchange and generally costs a fortune . . . However things change: IEX, a new exchange, recently opened and they are offering real time bid/ask data for free. Here's the API description: https://www.iextrading.com/developer/ This data should be good for active securities, but for securities less actively traded the numbers might be stale.
This is just a shot in the dark but it could be intermarket data. If the stock is interlisted and traded on another market exchange that day then the Yahoo Finance data feed might have picked up the data from another market. You'd have to ask Yahoo to explain and they'd have to check their data. Investopedia has one and so does marketwatch    I've always used marketwatch, and I have a few current competitions going on if you want me to send the link    They recently remodeled the website so it works on mobile and not as well on desktop    Don't know anything about the investopedia one though When you are placing an order with an online broker you should already know what exchange or exchanges that stock trades on. For example if you look up under Yahoo Finance: Notice how News Corp is traded both on the ASX and the Nasdaq. The difference is the shares traded on the ASX have the extension .AX, that is how you know the difference between them. When you are putting orders in with your online broker you will need to select the exchange you wish your order to go to (if your broker allows trading on multiple exchanges). So you should always know which exchange your order goes to. I've looked into Thinkorswim; my father uses it. Although better than eTrade, it wasn't quite what I was looking for. Interactive Brokers is a name I had heard a long time ago but forgotten. Thank you for that, it seems to be just what I need. http://www.moneysupermarket.com/shares/CompareSharesForm.asp lists many. I found the Interactive Investor website to be excruciatingly bad. I switched to TD Waterhouse and found the website good but the telephone service a bit abrupt. I often use the data presented on SelfTrade but don't have an account there. My broker collates the order book by price and marketplace, displaying the number of shares available at each level, sorted as in Victor's screencap. You can glean information from not just a snapshot of the order book but also by watching how it changes over time. Although it's not always a complete picture -- many brokers hold limit orders internally until the market is close, at which point they'll route to an exchange or trade internally. And of course skilled market participants know that there's people out there looking to glean information from the order book and will act to confuse the picture. The order book can show you: Combined with a list of trades (price & size, and whether it was a buy or sell), you can get a much more complete picture of what's going on with a stock than by looking at charts alone. "At the bottom of Yahoo! Finance's S & P 500 quote Quotes are real-time for NASDAQ, NYSE, and NYSE MKT. See also delay   times for other exchanges. All information provided ""as is"" for   informational purposes only, not intended for trading purposes or   advice. Neither Yahoo! nor any of independent providers is liable for   any informational errors, incompleteness, or delays, or for any   actions taken in reliance on information contained herein. By   accessing the Yahoo! site, you agree not to redistribute the   information found therein. Fundamental company data provided by Capital IQ. Historical chart data   and daily updates provided by Commodity Systems, Inc. (CSI).   International historical chart data, daily updates, fund summary, fund   performance, dividend data and Morningstar Index data provided by   Morningstar, Inc. Orderbook quotes are provided by BATS Exchange. US   Financials data provided by Edgar Online and all other Financials   provided by Capital IQ. International historical chart data, daily   updates, fundAnalyst estimates data provided by Thomson Financial   Network. All data povided by Thomson Financial Network is based solely   upon research information provided by third party analysts. Yahoo! has   not reviewed, and in no way endorses the validity of such data. Yahoo!   and ThomsonFN shall not be liable for any actions taken in reliance   thereon. Thus, yes there is a DB being accessed that there is likely an agreement between Yahoo! and the providers." Here are a couple of articles that can help highlight the differences between a broker and an online investment service, which seems to be part of the question that you're asking. Pay attention to the references at the end of this link. http://finance.zacks.com/online-investing-vs-personal-broker-6720.html Investopedia also highlights some of the costs and benefits of each side, broke and online investment services. http://www.investopedia.com/university/broker/ To directly answer your question, a broker may do anything from using a website to making a phone call to submitting some other form of documentation. It is unlikely that he is talking directly to someone on the trading floor, as the volume traded there is enormous. You can get this data from a variety of sources, but likely not all from 1 source.  Yahoo is a good source, as is Google, but some stock markets also give away some of this data, and there's foreign websites which provide data for foreign exchanges.    Some Googling is required, as is knowledge of web scraping (R, Python, Ruby or Perl are great tools for this...). "This functionality is widely available, not only on brokerage sites, but also financial management and even financial information sites.  For instance, two of the latter are Google Finance and Yahoo Finance.  If you are logged in, they let you create ""portfolios"" listing your stocks and, optionally, the size of your holdings in that stock (which you don't need if you are just ""watching"" a stock).  Then you can visit the site at any time and see the current valuations." The cause of incomplete/inaccurate financial data's appearing on free sites is that it is both complicated and expensive to obtain and parse these data. Even within a single country, different pieces of financial data are handled by different authorities.  In the US, for example, there is one generally recognized authority for stock prices and volumes (CQS), but a completely different authority for corporate earnings data (SEC).  For futures and options data the only authority is each individual exchange.  Each of these sources might have a vastly different interface to their data; some may have websites, others may have FTPs, others may have TCP datastreams to which you must subscribe, etc. Now throw in the rest of the world and all their exchanges and regulatory agencies, and you can see how it's a difficult job to gather all this information, parse it on a daily (or more frequent) basis, and check it all for errors. There are some companies (e.g. Bloomberg) whose entire business model is to do the above.  They spend tens of millions of dollars per year to support the infrastructure and manpower required to keep such a complex system working, and they charge their consumers a pretty penny in return. Do Google/Yahoo pay for Bloomberg data access just to display information that we then consume for free?  Maybe.  Maybe they pay for some less expensive reduced data set.  Or a data set that is less rigorously checked for errors. Even if they pay for the best data available, there's no guarantee that a company's last earnings report didn't have a glitch in it, or that Bloomberg's latest download from the Canadian Agency for Corporate Dividends and Moose Census-Taking didn't get cut off in the middle, or that the folks at Yahoo built a robust system that can handle a particular file's not arriving on time.  Bloomberg has dozens or even hundreds of employees focused on just this one task; Yahoo probably has 5. Moral: If you really need the best available data you must go to the source(s), or you must pay a provider to whom you can then complain when something is wrong.  With free data you get what you pay for. "Yes, Interactive Brokers is a good source for live data feeds and they have an API which is used to programmatically access the feeds, you will have to pay for data feeds from the individual data sources though.  The stock exchanges have a very high price for their data and this has stifled innovation in the financial sector for several decades in the united states. But at the same time, it has inflated the value and mystique of ""quants"" doing simple algorithms ""that execute within milliseconds"" for banks and funds.  Also RIZM has live feeds, it is a younger service than other exchanges but helps people tap into any online broker's feeds and let you trade your custom algorithms that way, that is their goal." You can register with an online broker. You can usually join most online brokers for free and only have to fund your account if you decide to place a trade. You may also check out the website of the actual companies you are interested in. They will provide current and historic data of the company's financials. For BHP you can click on the link at the bottom of this webpage to get a PDF file of past dividends from 1984. "TDAmeritrade, an online stock broker, provides banking services within their brokerage accounts. The service offers all of what you are looking for. HOWEVER, this service is only available for free with their ""Apex"" qualification.  Here is a tariff of their fees and services." Google Finance and Yahoo Finance have been transitioning their API (data interface) over the last 3 months. They are currently unreliable. If you're just interested in historical price data, I would recommend either Quandl or Tiingo (I am not affiliated with either, but I use them as data sources). Both have the same historical data (open, close, high, low, dividends, etc.) on a daily closing for thousands of Ticker symbols. Each service requires you to register and get a unique token. For basic historical data, there is no charge. I've been using both for many months and the data quality has been excellent and API (at least for python) is very easy! If you have an inclination for python software development, you can read about the drama with Google and Yahoo finance at the pandas-datareader group at https://github.com/pydata/pandas-datareader.