I replied before to a similar thread. http://www.elitetrader.com/vb/showthread.php?s=&postid=3051284&highlight=totalview#post3051284 What I said was: 1. Arcabook should contain more than top of book. Although NYSE owns Arca, they are separate exchanges with separate orderbooks, separate bid asks. For example, right now in C, at 4.86 NYSE is bid 2,148,700 shares while arca is only bid 723,000 shares. The data is not redundant, if you want a complete picture of liquidity you need both. There are also some stocks which only trade on arca, such as NUGT. 2. NASDAQ TotalView includes all the NASDAQ market makers and various other ecns I believe (not sure if it includes BATS/EDGA/EDGX depth of market, I believe it does). It doesn't overlap with NYSE Arca or NYSE. 3. NYSE Openbook just shows the NYSE limit orders, not ARCA or any of the orders on nasdaq totalview. --- If you daytrade and want decent executions, subscribe to all three. If the stock you're trading is 20.50 bid by 20.51 offer, for example, and you want to buy, you might just pay the offer at 20.51 if you have no level II data. However, if you have all three, you might notice that there are no bids on ARCA at 20.50 and if you put a bid there you are first in line and more likely to get a fill. Not only do you save a penny, but you get a rebate instead of a remove, saving you net-net a penny and a half per share ($15/1000). ======================================= I'm not sure if Trade Station has everything under Total View - usually Arca Book, Bats Book (BATS and BYX ECN), and Direct EDGE Book (EDGE-A and EDGE-X). However, NYSE Open Book will always just display the liquidity routed directly to New York. All is understood?
I'm still kinda confused as to what "Level III" actually is, and weirdly, have yet to find a definitive post on that -- seems like you might be a good person to ask. Maybe it's so obvious to most everyone that there's been no need to explain (lol)... but I've seen/gotten a fair number of seemingly conflicting opinions out there from people who otherwise appear to "know," so maybe I'm not the only one who's somewhat clueless about this. Is "Level III" just a semi-subjective term (as some have alluded to) that generally refers to a combined data feed *and* executable functionality that's only available to MMs? Is all of the data somehow consolidated for their use, either in-house or via 3rd party? Can the typical independent daytrader effectively assemble "Level III" capability to at least *see* all (or most?) of the same data that a MM can by subscribing to ArcaBook, TotalView and OpenBook in addition to the "standard" DMA Level II feed... with the only difference being that a non-MM would obviously lack the direct executional capability that a MM has via his/her platform? ("Look but don't touch.") Thanks.