joa...@swbell.net (John McKown) writes: > I think this is an artifact that the 3270 data stream is really designed to > be "half duplex", like the old walkie-talkies. Each side tells the other > that it has control of the transmission. This is especially true in TSO. > Now, I do remember z/VM's or maybe CMS's control of the 3270 was more "full > duplex" like.
there was an extremely annoying problem that (half-duplex, real) 3270 keyboard would lock up if you were typing at the sametime some time there was a screen write. once there was (software) 3270 terminal emulation ... on PC ... the software emulation could mask the annoying half-duplex operation and not lock the keyboard. in the 70s ... with real 3272 controller & 3277 keyboards ... there was a hardware hack done to mask the really annoying and frustrating half-duplex operation You unplug the 3277 keyboard from the 3277 head and plug in a small (specially built hardware box) fifo and then plug the keyboard into the FIFO. The FIFO box was able to queue keystrokes that would happen during any periods that the screen was being written. With move to 3278/3279 ... lots of the electronics that had previously been in the 3277 terminal ... were moved backed in 3274 controller ... and lots of the human factor (hardware) hacks to the 3277 no longer worked. Fortunately it was still possible to configure 3277 to work with 3274 controller ... so I kept my 3277 until able to replace it with pc/at & terminal emulation. Note that ANR (aka 3277) coax protocol had lot higher thruput than DCA (aka 3278) coax protocol. So even after getting pc/at with software emulation ... there was still preference for 3277 (ANR) adapter card (so uploads/downloads ran significantly faster). couple past posts (including reference to ANR having three times the thruput of DCA): http://www.garlic.com/~lynn/2007r.html#10 IBM System/3 & 3277-1 http://www.garlic.com/~lynn/2007t.html#40 Why isn't OMVS command integrated with ISPF? http://www.garlic.com/~lynn/2007t.html#42 What do YOU call the # sign? http://www.garlic.com/~lynn/2008h.html#9 3277 terminals and emulators http://www.garlic.com/~lynn/2008r.html#46 pc/370 there wasn't anything inherent in 3270 that was half-duplex ... it was the operation of the channel to controller and the controller to the head. In the early 80s, STL lab was starting to burst at the seams ... and the decision was made to move 300 people from the IMS group to offsite building. They had looked at remote 3270 terminals into the STL lab vm370/cms development machines (not development for vm370/cms ... but development for lots of database and MVS products). Remote 3270 terminal thruput and operational characteristics where deemed totally unacceptable. It was eventually decided to deploy NSC HYPERChannel ... as "channel extender" over T1 microwave channel with local 3270 controllers and local 3270 terminals at the remove site. I got to totally (re)write the drivers to support HYPERChannel remote operation (another hobby, they used to joke that I worked 1st shift in bldg. 28, 2nd shift in the disk labs, 3rd shift in STL ... and weekends/4th shift at HONE datacenter up the peninsula). I treated it had high speed full-duplex operation ... with HYPERChannel boxes masking a lot of the half-duplex operation of the 3270 controllers. misc. past posts related to HSDT project, HYPERChannel boxes &/or supporting the IMS group: http://www.garlic.com/~lynn/subnetwork.html#hsdt STL had been in the habit of configuring machines with both 3270 controllers and disk controllers on same/all available channels. With the HYPERChannel extenders ... not only did the remote IMS group didn't notice any difference in system response (being at the end of T1 microwave link) ... system thruput actually improved. 3270 controllers were really slow in lots of ways. Having 3270 controllers on same channel with disk controllers ... resulted in lots of high channel busy (not so much data transfer but latency for 3270 controllers handling control operations) ... resulting in lots of channel contention with disk controllers. Moving the 3270 controllers directly off the mainframe channels ... replacing them with HYPERChannel boxes ... which were much faster and had much lower channel busy for identical 3270 channel operations ... resulted in increase in disk i/o thruput. -- 40+yrs virtualization experience (since Jan68), online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
