The first device to support "disconnect" was the 3330 which also connected to a 3830. Prior to that IO in both directions tied up the entire path from CPU to device and back for the duration (2314, 2311 dasd).
The flow of a "typical" IO request: Channel passes commands to 3830 and disconnects. 3830 passes commands to "logic" boards in 3350A2 and disconnects "logic boards" issue commands to individual device (3350A2/B2) and disconnect. The following processing will then occur: Device handles requests and reconnects to logic boards. "logic boards" reconnect to 3830 3830 communicate to CPC Data transfer occurs. Note the entire path (device-logic boards-3830-channel) is "locked" for the duration of the data transfer. The paradigm has generally not changed since the "old days". The major differences between the "old days" and today: There is no longer a "separate" control unit e.g. 3830 This logic is now in the DASD device itself. The advent of cache controllers allows for the reconnection process to be performed "asynchronously". Again this is packaged in the device itself. Once the data has been passed from the device to the cache, the devices are free to handle other requests. This allows for greater DASD thruput. BTW, between the 3830/3350 and "modern DASD". There were stand-alone 3880/3380 and 3990/3390 "control units" with cache capability. The stand-alone logic represented by the 3830 , 3880 and 3990 control units have been absorbed into the device itself. Externally it is "CPU-->DASD box" Internally, all of the components of the "original paradigm" are still present with the detail obscured by the hardware. -----Original Message----- From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On Behalf Of R.S. Sent: Wednesday, May 15, 2019 7:59 AM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Ancient DASD connectivity (this is mostly historical question) I'm trying to understand the role of old boxes in DASD connectivity. From IODF/HCD point of view we have CPC-channels-CU-some_cable-DEVice Nowadays in real world we have CPC-ficon-DASDbox and DASDbox is both CU+DEV (emulated). In the old days there was a Storage Control Unit, i.e. 3830 and disk controller within disk cabinet, i.e. 3350-A2 So, we have CPC-cable1-3830-cable2-3350A2controller-internal_cable3-disk. I'm trying to understand separation of duties between 3830 and 3350A2 controller. What was defined as CU - it was 3830 or controller within 3350 cabinet? Which cable was a channel (Bus&Tag)? I guess it is "cable1" connecting CPC and 3830. Not to mention that some old reference manual's diagram shows yet another box between CPC and 3830 SCU. -- Radoslaw Skorupka Lodz, Poland ====================================================================== Jeśli nie jesteś adresatem tej wiadomości: - powiadom nas o tym w mailu zwrotnym (dziękujemy!), - usuń trwale tę wiadomość (i wszystkie kopie, które wydrukowałeś lub zapisałeś na dysku). 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