Hi Guys, First, I am not sure if this forum was made for questions like this, but since its not for commercial reasons I hope you do not mind. I am currently writing my Master Thesis about Dark Pools, but to be honest I am getting a bit confused with some of the terms. It would be crucial for me to understand how co-location with Dark Pools works. Who co-locates to whom? I understand (at least I hope so) that the basic concept of direct feeds is to gain an advantage in terms of speed compared to SIP subscribers. Nanex visualizes this very well I guess: http://www.nanex.net/aqck2/4599.html So an exchange transfers its quotes and the faster I receive them, the better I can react (roughly speaking). But what does it mean, when for instance Level ATS writes in their FAQ: " LeveL ATS does not offer the ability to co-locate with the matching engine". Whats the point in co-locating with the matching engine if the Dark Pool itself receives the quotes via SIP (in case of Level from Thesys in New Jersey)? Why do most Dark Pool operators do not disclose this kind of information in their "manuals"? Barclays just writes, that they determine the current NBBO using direct exchange feeds AND the SIP, but not a word about if subscribers can co-locate with their matching engine. is this a valid question or do I confuse things here? Im sure for most of you this questions sound a bit dumb, but my Finance classes at University were quite plain and I am still struggling to understand the mechanics of HFT. Id be most grateful if some of you could swallow their pride and take the time to answer a newb like me