After a while, ThinkPad530CS intruded in them and organized the prottype of today's "intranet in chaos" in my house. This port changer relayed the file transfer among the chaos.
On that day I was deeply impressed to the file transfer with "LAPLINK", a file transfer software using RS-232C & reversal serial cable.
I talked big like this; "I'll use this ThinkPad in stand-alone and for only business. So there is no need to connect them with ethernet."
I, now connecting over 7PCs with ethernet, getting scattered and lose the recent shared files, and taking mistake for file synchronization and overwrite the old files for the recent one, was young on these days.