1. A computer-implemented method of installing a program on a first computer system comprising: calculating a memory space requirement to install files of a program; determining that a first available memory space in a first memory of a first computer system is smaller than the memory space requirement, wherein the first memory is a default memory for installing the program; upon determining that the first available memory space in the first memory is smaller than the memory space requirement, prompting a user to connect a second memory with a second available memory space to the first computer system, wherein the second memory is a selectively attachable portable memory, and wherein the second memory is unconnected to the first computer system at the time of prompting; upon determining that the user connected the second memory in response to the prompting, computing a sum of the first available memory space and the second available memory space; determining whether the sum is greater than or equal to the memory space requirement to install files of the program; identifying a first set of install files and a second set of install files, wherein the first set of install files includes install files that must be installed for the program to run and the second set of install files includes install files that do not need to be installed in order for the program to run; and installing the first set of install files in the first memory space and the second set of install files in the second memory space that was connected to the first computer system in response to the prompting when the sum is greater than or equal to the memory space requirement.