Wall Street will never be the same. In addition to an inevitable overhaul of the financial regulatory framework, the credit crisis has vastly changed the competitive landscape.

With the market turmoil pushing many broker-dealers toward bankruptcy, at least four major firms were forced to find merger partners or became acquisition targets. Now those firms are facing the enormous hurdle of unifying their trading operations. But combining two major financial firms with very distinct cultures, products, services and technol-ogy infrastructures is a monumental challenge.

The first acquisition was set in motion in early 2008 as Bear Stearns teetered on the brink of collapse and J.P. Morgan swooped in to buy out the firm. Then, over one frantic September weekend, Lehman Brothers filed for bankruptcy and Merrill Lynch was acquired by Bank of America. Eventually Lehman's North American operations were purchased by Barclays Capital, and its Europe, Middle East and Asia-Pacific operations were acquired by Nomura Holdings.

The remaking of these firms and their trading businesses already has taken months of work, and there likely is more pain ahead. But as the integration efforts have progressed, Advanced Trading was given an exclusive inside look at how the firms' trading operations are taking shape. Like the broker-dealers' buy-side clients, we wanted to know what the firms' newly merged algorithmic trading offerings look like and which underlying trading platforms will prevail. And perhaps most important to their clients, we also examined who ultimately will lead the broker-dealers' trading operations.