The US equity market does about 4b in transactions a day; let&#x27;s say the average trade size is $1000 dollars (probably an aggressive estimate; I&#x27;d expect it actually to be higher), and you record the ticker (4bytes) + price(8) + quantity(8) for all the transactions, you&#x27;d get --<p>(4+8+8)<i>(4e9&#x2F;1000) </i> 252 (trading days) &#x2F; 1e9 = 20GB&#x2F;year<p>lets say you have these for 100 years, you&#x27;d still only have 2TB. And this if for the <i>entire</i> US equity market -- NYSE is only one of 11 protected exchanges (and only trades tape A), so the above estimates are pretty optimistic.<p>Now, if you wanted to record every <i>message</i> and not just every transaction, then you get into serious data (on the order of ~2-5TB&#x2F;day).