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Specialist financial services analyst firm TowerGroup has calculated that $1.7bn (£1.2bn) of that sum will be spent on hardware, with the remaining $1.5bn going on services and software.
New York-based TowerGroup has estimated that some 30,000 securities trading desks were destroyed when the seven WTC buildings collapsed, and that a further 15,000 to 20,000 will have to be replaced in damaged buildings adjacent to the site.
The figures have been calculated on the basis that 16,000 trading desks need to be reinstated - which includes turrets (a complex telephone system for traders) and workstations with flat screen displays - at a cost of $52,000 a piece. A further 34,000 general workstations need replacing at $5,000 each.
TowerGroup believes 5,000 Unix servers and 8,000 Intel servers were destroyed in the terrorist attacks, leaving a replacement bill of around $370m, while $300m will be spent on printers, hubs, switches, storage and general networking hardware.
Larry Tabb, vice president of TowerGroup's Securities & Investments Research Practice said securities firms face a bill of some $1.5bn to install, configure and manage the implementation of this equipment.
"Much of this [$1.5bn] will be allocated to internally staffed projects. However, there will be a great demand for consulting and contract services to develop, install and implement new trading stations and firms' technology infrastructure," said Tabb.
The company believes the majority of this money would be spent over the next 12 to 24 months. It also claims that most of the data and software at risk when the towers collapsed on 11 September had been saved thanks to disaster recovery strategies and contracts.
All of the companies affected are currently either working from their disaster recovery sites, or at secondary or temporary offices. It could take some time before suitable new sites are found to house the trading community.
"Trading floors, by their nature," Tabb explained, "need to be large rooms without many walls or pillars, with clear sight lines, and capable of supporting hundreds of traders or salespeople sitting elbow-to-elbow surrounded by vast amounts of technology. Trading stations traditionally utilise at least two workstations [Wintel and possibly Unix], which drive four to eight 19 to 21in flat-screen monitors."