Hello,
This is a bug report. I tried to use the reporting system, but it did not
seem to be appropriate. So, I will give a narrative:
This is what happened.
I decided to install Debian on my small machine (Asus eeePC 900A, 1GB
ram, 4GB storage). So I selected debian-9.3.0-i386-xfce-CD-1.iso and
put it onto a flash memory stick. Installation went ok, but
later on when I did "apt install gcc", the installation program
requested the insertion of the installation disk in the drive
/media/cdrom. Why?
Examination.
The /etc/apt/sources.list file had "deb: cdrom:[<installation>..." as
the first entry, and was not commented out. My installation medium
was wrong!