Technology companies have been beefing up their portfolios by buying up service providers, which are proven to be attractive targets with their relatively high-margin businesses and stability during tough economic times.

On Monday, Xerox Corp said it plans to buy Affiliated Computer Services Inc in a deal valued at $5.4 billion.

Xerox Chief Executive Ursula Burns said the company's revenue from services will triple to an estimated $10 billion next year from $3.5 billion in 2008 after the deal.

 Other recent events:
 -- On Sept. 21, Dell Inc offers to buy Perot Systems Corp for about $3.9 billion, paying a steep 67.5 percent premium.
 -- In August 2008, HP acquired EDS for $13 billion.
WORLD'S BIGGEST IT SERVICES COMPANIES
1) IBM
Market capitalization:        : $159 billion
Percentage of services revenue: 57.9 percent
Employees                     : 398,455    
Specialization                : Servers, IT services, software
2) Hewlett-Packard
Market capitalization:        : $111 billion
Percentage of services revenue: 35.3 percent
Employees                     : 321,000   
Specialization                : PCs, servers, printers, IT services
3) Dell
Market capitalization:        : $30 billion
Percentage of services revenue: 16.4 percent
Employees                     : 76,500 (excl Perot)
Specialization                : PCs, servers, IT services
4) Infosys 
Market capitalization:        : $27 billion
Percentage of services revenue: 96 percent 
Employees                     : 103,905    
Area of specialization        : IT outsourcing
5) Accenture
Market capitalization:        : $26 billion
Percentage of services revenue: Consulting - 57/Outsourcing - 43
Employees                     : 186,000
Areas of specialization       : Consulting, IT services, outsourcing
6) Tata Consultancy Services 
Market capitalization:        : $24 billion
Employees                     : 143,000   
Area of specialization        : IT outsourcing
7) Wipro 
Market capitalization:        : $17 billion
Percentage of services revenue: 79 percent
Employees                     : More than 95,000
Area of specialization        : IT outsourcing
8) Cognizant 
Market capitalization:        : $11 billion
Employees                     : 64,100    
Specialization                : IT services, outsourcing, consulting
9) Computer Sciences
Market capitalization:        : $7.7 billion
Employees                     : 92,000     
Specialization                : IT services, outsourcing
 (Sources: Company websites and filings, Reuters data)
 (Reporting by S. John Tilak, Manasi Phadke in Bangalore)