The difference between Strats within different groups

I have found the description on Goldman Sachs' web:
Roles within Securities Strats
Securities Strats play important roles in several areas. Some Strats sit on trading desks, creating cutting-edge derivative pricing models and developing empirical models to provide insight into market behavior. Others develop automated trading algorithms for the firm and its clients, taking an active part in the increasing shift from voice to electronic trading. A third group works directly with the firm’s sales force and clients, analyzing exposures, structuring transactions, and applying quantitative concepts to meet client needs. Between these teams, Core Strats design and develop complex parallel computing architectures, electronic trading tools, and advanced algorithms.
Roles within Investment Banking Strats
Investment Banking Strats collaborate with marketers and bankers in Investment Banking and the Financing Group to create quantitative strategies and analyses that lead to value-added transactions with clients. In the course of business, Investment Banking Strats use models to simulate and evaluate financial statements, funding, structuring and hedging strategies and risk management alternatives. Investment Banking Strats possess both general and specialized skill sets, developing expertise across products, markets, industries and strategic transactions.
Roles within Investment Management Strats

Investment Management Strats work in Asset Management and Wealth Management. Investment Management Strats collaborate with Portfolio Managers and Traders to analyze portfolios, create investment algorithms, and build pricing models and risk management tools for derivatives and complex cash securities traded across the firm’s fund complex. They may also work with clients – both private and institutional – to understand and analyze client investment needs, portfolios (including those employing external managers) and investment strategies to meet specific needs. The work involves developing a thorough understanding of the full range of investment products and strategies offered by the firm, an ability to capture the characteristics of those investments in mathematical models and the creation of infrastructure to make those analyses reusable and scalable across our businesses.

However, I could not fully understand the difference between different groups, like Securities and Investment Management. They are both in the buy side and they focus on making profit through trading in the market. From my point, the difference might lie in that Securities may pay more attention to some particular stocks or futures while Investment Management would pay more attention to how to form the portfolio. Is this understanding correct? And what specific background should one has to make him suitable for the Securities Strats and Investment Management Strats?

Thanks for your patience and kind reply in advance.:)
Here is an oversimplification:
Securities: PDEs and time series
IB: Financial statement forecasting
IM: Asset allocation
Thanks for your reply. Could you please explain the difference between securities and IM more? Do strats in securities focus more on certain stocks or futures' trend while strats in IM focus more on the method to determine the weight in the portfolio? What promotion could be made in these two departments?