What is information system architecture?

Architecture means the equipment. For example, hard discs originally used MFM (Modified Frequency Modulation) to write and read discs. Then they switched to another abbreviation, and then they put all the electronics in the hard drive, (IDE, Integrated Drive Electronics) so the drive no longer needed a separate controller card. Now they use a system called SATA. Each of these is a different architecture, meaning the equipment is different. A difference in software only involves an updated driver.