The less obvious problem with unlabeled tapes was you could miss blocks and not know. Most systems at least checked block counts at EOF.
Sent from Yahoo Mail for iPhone On Friday, November 7, 2025, 3:32 PM, Phil Smith III <[email protected]> wrote: Ah, sorry, I meant to say: it was a physical label on the tape. Kinda an important detail I omitted! So it wasn't "security" per se, more like the Luhn on a credit card, to avoid entry error (in this case, "grab error"). -----Original Message----- From: IBM Mainframe Discussion List <[email protected]> On Behalf Of Paul Gilmartin Sent: Friday, November 7, 2025 4:28 PM To: [email protected] Subject: Re: Ancient history: 3420s On Fri, 7 Nov 2025 14:42:59 -0500, Phil Smith III wrote: >Lots of unlabeled tapes, especially on VM. > >This was a backup for that. > How was that "4-character hash " communicated to the operator? >On 11/7/2025 9:52 AM, Phil Smith III wrote: >> >> The 3420 reminds me: back at UofW, they had a system that would create a >> 4-character hash (I assume) from the tape number. So when you asked for tape >> 1234, the operator would pull it and when they responded to the mount >> request, they had to enter that 4-character value. If they'd accidentally >> pulled 1235 instead, there would be a mismatch and it would tell them to try >> again. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
