http://www.allaboutcircuits.com/vol_5/chpt_7/1.html i have read this article and having few questions in my mind. i am intrested to learn about these simulation software . i have used pspice 9.1 student version . PSPICE, a widely available PC version distributed by the MicroSim Corporation whilst HSPICE from Meta-Software has been popular for workstations . but these softwares are costly . The parent of all these software is old free spice program from Berkeley university . I want to ask few questions 1- if we have free (old)spice available then why we need these costly software. 2- which platform(operating system) is required for spice program . 3- can i use BSIM model in pspice and Hspice. 4-Like in spice we make an input text file or deck and give it to software for simulation , can we do the same with pspice instead of making schematic and creating netlist automatically we just give our own input file and simulate circuit. 5- i needed spice software , tell me from where to get it.