ISTR there were such floppies that loaded CPU microcode, similarly for DASD and tape controllers I believe.
You used to have to do “IML” (“Initial Microprogram Load”) of CPU’s and some peripheral control boxes before you could use them normally, and the IML source was one of those floppies. Some hardware fixes and upgrades were just a new floppy and IML. Peter From: IBM Mainframe Discussion List <[email protected]> On Behalf Of Radoslaw Skorupka Sent: Thursday, July 11, 2024 12:00 PM To: [email protected] Subject: Mainframe history - 12 inch floppies? I just found information in some book that IBM mainframes used 12 inch floppy diskettes. Late 70's. Anybody heard about such diskettes? -- This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
