How the 80 x 24 terminal display came about

[ChickenMan]

I found this fascinating blog about how the 80 x 24/25 screen, as used in the Microbee and others, came about.  Check it out at

http://www.righto.com/2019/11/ibm-sonic-...Uws6HeBcBg

[someone]

Someone has installed more IBM 3270, 5250 (and similar) and Token Ring and Coax SNA adapters that one can imagine and that's a huge number only slightly less than the 100's of thousands of PCs that someone has deployed, fixed, upgraded.

The advent of the cheap twisted pair 100mbps Fast Ethernet killed the 4/16MBPS Token Ring and SNA.
100VG- ANYLAN was HP's 100Mbps Ethernet standard over Cat 3 twisted pair wiring that used Token Ring token passing for deterministic high performance. It died a premature death.
Unlike Fast Ethernet which used 2 pairs, 100VG- ANYLAN used all 4 pairs thus required the use of 100VG- ANYLAN network switches.
BTW - VG=Voice Grade

Did you know that IBM deliberately wounded the IBM PC's parallel port to ensure that it did not compete against it's terminal products.
I.E. Why sell a PC when you can also sell the customer a terminal.
It was only during subsequent updates that the parallel port got EPP and ECP capabilities.

Also be aware that 3270 and similar terminals often use Block mode communications. e.g. sending a whole screen of data.
The terminal and the FEP (Front End Processor) that it is attached did not communicate with the Mainframe(s) until the RETURN key was pressed.
For the IBM PC it was a specifically nominated Enter Key - most often the Enter key on the Number pad.
The other Enter keys were assigned another function.

HLLAPI (and later EHLLAPI) was used with Terminal Emulators on PCs to provide additional functionality like sending files with email.

Another strange IBM product was to allow IBM PCs with SNA Coax connectors that communicated with FEPs, Novell Netware access.
It was damned expensive at about $70K per FEP.