When completed in 1973, 2 World Trade Center (the South Tower) became the second tallest building in the World – behind its twin, 1 World Trade Center.
The South Tower's rooftop observation deck was 1,362 ft (415 m) high and its indoor observation deck was 1,310 ft (400 m) high.
The World Trade Center towers held the height record only briefly; the Willis Tower in Chicago, finished in May 1973, reached 1,450 feet (440 m) at the rooftop.
Throughout its existence, however, the South Tower had more floors (at 110) than any other building.
This number was not surpassed until the advent of the  Burj Khalifa, which opened in 2010.

Of the 110 stories, eight were set aside for technical services in mechanical floors (floors 7/8, 41/42, 75/76, and 108/109), which are four two-floor areas that evenly spaced up the building.
All the remaining floors were free for open-plan offices.
Each floor of the towers had 40,000 square feet (3,700 m²) of space for occupancy.
The original Two World Trade Center had 95 express and local elevators.
The tower had 3,800,000 square feet (350,000 m²) of office space.

Initially conceived as a complex dedicated to companies and organizations directly taking part in "world trade", the South Tower, along with 1 World Trade Center (also known as the North Tower) at first failed to attract the expected clientele.
During the early years, various governmental organizations became key tenants of the World Trade Center towers including the State of New York.
It was not until the 1980s that the city's perilous financial state eased, after which an increasing number of private companies – mostly financial firms tied to Wall Street — became tenants.
During the 1990s, approximately 500 companies had offices in the complex including many financial companies such as Morgan Stanley, Aon Corporation, Salomon Brothers, and the Port Authority itself.
The basement concourse of the World Trade Center included The Mall at the World Trade Center, along with a PATH station.

Electrical service to the towers was supplied by Consolidated Edison (ConEd) at 13,800 volts.
This service passed through the World Trade Center Primary Distribution Center (PDC) and sent up through the core of the building to electrical substations located on the mechanical floors.
The substations stepped down the 13,800 primary voltage to 480/277 volt secondary service, and then further down to 208/120 volt general power and lighting service.
The complex also was served by emergency generators located in the sub-levels of the towers and on the roof of 5 WTC.

The 110th floor of 1 World Trade Center (the North Tower) housed radio and television transmission equipment; access to the roof of 1 WTC was controlled from the WTC Operations Control Center (OCC) located in the B1 level of 2 WTC.

At 9:03 a.m. EDT on September 11, 2001, five terrorists crashed United Airlines Flight 175 into the southern facade of the South Tower.
Three buildings in the World Trade Center complex, including 2 WTC, collapsed due to fire-induced structural failure.
The light construction and hollow nature of the structures allowed the jet fuel to penetrate far inside the towers, igniting many large fires simultaneously over a wide area of the impacted floors.
 The fuel from the planes burned at most for a few minutes, but the contents of the buildings burned over the next hour to hour and a half.

The fires might not have been as centrally positioned, nor as intense, had traditionally heavy high-rise construction been standing in the way of the aircraft.
Debris and fuel would likely have remained mostly outside the buildings or concentrated in more peripheral areas away from the building cores, which would then not have become unique failure points.
 In this scenario, the towers might have stood far longer, perhaps indefinitely.
The fires were hot enough to weaken the columns and cause floors to sag, pulling perimeter columns inward and reducing their ability to support the mass of the building above.
The South Tower collapsed at 9:59 a.m. after burning for 56 minutes in the fire cau
When completed in 1973, 2 World Trade Center (the South Tower) became the second tallest building in the World – behind its twin, 1 World Trade Center. The South Tower's rooftop observation deck was 1,362 ft (415 m) high and its indoor observation deck was 1,310 ft (400 m) high. The World Trade Center towers held the height record only briefly; the Willis Tower in Chicago, finished in May 1973, reached 1,450 feet (440 m) at the rooftop. Throughout its existence, however, the South Tower had more floors (at 110) than any other building. This number was not surpassed until the advent of the  Burj Khalifa, which opened in 2010.
Of the 110 stories, eight were set aside for technical services in mechanical floors (floors 7/8, 41/42, 75/76, and 108/109), which are four two-floor areas that evenly spaced up the building. All the remaining floors were free for open-plan offices. Each floor of the towers had 40,000 square feet (3,700 m²) of space for occupancy. The original Two World Trade Center had 95 express and local elevators. The tower had 3,800,000 square feet (350,000 m²) of office space.
Initially conceived as a complex dedicated to companies and organizations directly taking part in "world trade", the South Tower, along with 1 World Trade Center (also known as the North Tower) at first failed to attract the expected clientele. During the early years, various governmental organizations became key tenants of the World Trade Center towers including the State of New York. It was not until the 1980s that the city's perilous financial state eased, after which an increasing number of private companies – mostly financial firms tied to Wall Street — became tenants. During the 1990s, approximately 500 companies had offices in the complex including many financial companies such as Morgan Stanley, Aon Corporation, Salomon Brothers, and the Port Authority itself. The basement concourse of the World Trade Center included The Mall at the World Trade Center, along with a PATH station.
Electrical service to the towers was supplied by Consolidated Edison (ConEd) at 13,800 volts. This service passed through the World Trade Center Primary Distribution Center (PDC) and sent up through the core of the building to electrical substations located on the mechanical floors. The substations stepped down the 13,800 primary voltage to 480/277 volt secondary service, and then further down to 208/120 volt general power and lighting service. The complex also was served by emergency generators located in the sub-levels of the towers and on the roof of 5 WTC.
The 110th floor of 1 World Trade Center (the North Tower) housed radio and television transmission equipment; access to the roof of 1 WTC was controlled from the WTC Operations Control Center (OCC) located in the B1 level of 2 WTC.
At 9:03 a.m. EDT on September 11, 2001, five terrorists crashed United Airlines Flight 175 into the southern facade of the South Tower. Three buildings in the World Trade Center complex, including 2 WTC, collapsed due to fire-induced structural failure. The light construction and hollow nature of the structures allowed the jet fuel to penetrate far inside the towers, igniting many large fires simultaneously over a wide area of the impacted floors.  The fuel from the planes burned at most for a few minutes, but the contents of the buildings burned over the next hour to hour and a half. 
The fires might not have been as centrally positioned, nor as intense, had traditionally heavy high-rise construction been standing in the way of the aircraft. Debris and fuel would likely have remained mostly outside the buildings or concentrated in more peripheral areas away from the building cores, which would then not have become unique failure points.  In this scenario, the towers might have stood far longer, perhaps indefinitely. The fires were hot enough to weaken the columns and cause floors to sag, pulling perimeter columns inward and reducing their ability to support the mass of the building above. The South Tower collapsed at 9:59 a.m. after burning for 56 minutes in the fire cau
2 World Trade Center