T A unit attached to a CU; it was the CU that attached directly to the channel. There is some overloaded nomenclature here; the control function of an A unit is entirely different from a control unit.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on behalf of Alan Altmark <alan_altm...@us.ibm.com> Sent: Friday, May 17, 2019 10:02 AM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: Ancient DASD connectivity On Thu, 16 May 2019 15:26:45 +0000, Seymour J Metz <sme...@gmu.edu> wrote: >Well, for some devices the CU and device were in the same box, e.g., 2501. Yes. A-units (Axx models) often include(d) at least one, possibly two or even four, I/O devices, with B units (Bxx models) providing expansion. Last CU standing in the A/B world was, I think, the IBM 3590, but it all went out the window when the 3592s made their debut. While it was interesting for IBM to wear it's engineering designs on its visible sleeve, it was confusing. Model numbers today are more expressions of marketing than of the underlying technology. Fun times. Alan Altmark IBM ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
