What exactly types and models represent in Thinkpads?

[Param]

I could find there are many Types and models for Thinkpad T61 or Txx

eg. Type: 6439
Model: CTO

What are those really? will there be any feature difference in the models of the same Thinkpad series?

While purchasing do we have option to select any specific types and model?

[Harryc]

There are hundreds of variables depending on features. Study the tabook for T61 then post any questions you may have. Basically you can't order a specific model off of the retail Lenovo site, but you should be able to ask an agent for a specific model, as long as it is standard and not CTO.
ftp://ftp.software.ibm.com/pc/pcinstitu ... tabook.pdf