Engineers that built the International Space Station understood that it wouldn’t be a good idea to use computers that are attached directly to the structure of the station. Repair, upgrade and maintenance tasks would potentially be difficult. Laptops are much more flexible and they already provide enough performance level for typical tasks in the ISS. At the moment, there are about eighty laptops used throughout the station, most of them are Lenovo T61P and there are also the older Lenovo A31P Thinkpad units.
On the US module, computing tasks are performed by seven laptops, which are also called the Portable Computer System or PCS. They are based on the open source Linux OS and connected with the station as remote terminals. On the Russian module, there are also seven equivalent laptops with the similar Linux software platform. They are used only to provide commands for the Russian segment.
In the Japanese segment, there are eight laptops with their own unique user interface. The European segment has only two laptops and a dozen of laptops are required to manage payloads operations. The remaining laptops are called Station Support Computers (SSC) and they are assigned in the Ops LAN network.