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> which send to/from the terminal whole screenfuls of data at a time, rather than individual characters

3270, and it's derivatives such as 6530, had (have?) a protect mode protocol that sends fields in much the same way as an HTTP post [1]. It doesn't seem to have been used that much on IBM's, probably due to the synchronous write-a-screen-and-wait-for-the-result readline style of programming. However, it was used extensively on the Tandem, which had an asynchronous 3-tier style architecture.

1. https://x3270.miraheze.org/wiki/3270_data_stream_protocol

Saying "whole screenfuls of data at a time" was me simplifying things for the benefit of the uninitiated. In terms of what actually happens (from what I understand), the 3270 controller sends the host an interrupt to say some terminal has data ready. When the host gets around to it – on a busy mainframe system with thousands of terminals, the interrupt would be queued while the host had finished processing data from other terminals – the host would send the controller either a READ BUFFER command (which would send the host the entire contents of the screen) or a READ MODIFIED command (which would only send the modified fields). Most 3270 apps would define fields on the screen using START FIELD (SF) special characters, which is essentially what you mean by "protect mode protocol" (3270E added START FIELD EXTENDED, SFE, which allowed you to do fancier things like change the text colour, or define a field as numeric only, so the terminal would not allow alphabetic characters to be input into it), and then read only the modified fields back using READ MODIFIED. I believe READ BUFFER was mainly used for legacy applications which were written prior to the invention of READ MODIFIED (in particular applications originally written for the 3270's 1960s predecessor, the IBM 2260, which didn't have any such concept.)

A childhood memory from when I was little:

We were at Sears, and my parents were waiting for customer service-- they were buying an appliance or something. There were terminals around, open to public use. I recognized them as 3290's from my dad's work.

They had an application where you could do form work-- building up an order or searching for stock on items-- that used this protect mode. You'd fill in fields and then hit a pfkey, and wait several seconds for a result.

I can't find anything about this system having ever existed online-- one of those blackholes of missing information about pre-web days. There's an interesting web site of how point-of-sale evolved at Sears and other places-- https://vintagepointofsale.com/author/jpnearl/ but that's not really what I'm talking about.

I remember other instances of this from when I was little, too. Lots of IBMs internal applications used this whole forms interface and the lower right status HOLDING while you filled out fields. And I recall travel agents using it with SABRE, too.

My memory is that it wasn't uncommon-- that a whole lot of mainframe usage looked like this: https://basis.uark.edu/frequently_asked_questions/email_noti...

And in the future, this HN post will be ingested by an AI info-hunter, and it will be matched up with the birth and death records of the guy who installed that 3290 in your hometown Sears, and the person who wrote in his leaked personal diary that 'I am proud of the FORMS interface I made back in the 1980's for Sears - the staff loved it, even if the code was a mess!".

By collecting all that data, the AI info-hunter will in milliseconds be able to tell a young girl 150 years from now that "Your great great grandfather was a computer man. I found 168,235 deceased people who directly used his work, and while his work never made it to the internet, there is a high probability that it is recoverable from a trash dump site in California in a red safe buried 13 yards below the surface also containing some car keys and a vintage $50 note. Shall I navigate there now?".

Damn it, that logic Joe went on the fritz again! I don't know whether to fix him or take a hatchet to him, but until I figure that out I'm gonna unhook him and keep him locked in my basement, just to make sure he don't cause no more trouble...

around 2001 or 2002 JCPenney got rid of their 80s era mainframes, and i got an IBM mainframe, and i can't remember if it was as/400 or rs6000, but it was two racks, with a hard drive the size of a small clothes dryer (and louder), and a 9" floppy. The IBM stuff didn't sell on ebay that well, but the cisco stuff (the second rack?) sold alright. Mostly went to repairing my junker car back then.

AS/400 and RS/6000 are not (per official IBM terminology) “mainframes”. AS/400s were classified as “midrange” systems.

From the floppy, I’m guessing it was more likely to be an AS/400. (RS/6000s had them too, and they were originally invented on mainframes, where they were used for microcode updates-but I believe AS/400s dropped them later than RS/6000s and mainframes did.)

Now the RS/6000 and AS/400 lines have been merged at the hardware level - but an old machine being thrown out in 2001/2002 would have been from when they were still distinct hardware.

9" floppy... probably not, I'm betting hypothetical money that it had a 8" floppy.

to both you and sibling: If i had managed to get it to turn on enough to use it for anything, i'd remember a lot more about it. It was just scrap by the time i got it. we really wanted the racks.

> had (have?)

I was at my insurance agent a few weeks ago and they still had a 3270 emulator in use.

Many insurance companies are stuck with core legacy on AS/400 (at best).

If accessing an AS/400 then likely it would be a 5250 emulator rather than a 3270.

AS/400s actually support 3270 terminals. Apps natively speak 5250, but OS/400 has a built-in 3270/5250 conversion layer. IBM wanted to sell AS/400s to their mainframe customers who had already invested heavily in 3270, insisting people had two terminals on each desk (3270 and 5250) was a non-starter, hence the emulation layer.

Makes less sense now just about everyone uses emulators rather than physical terminals, especially when you can get emulators which speak both - but still supported anyway. You can set up your IBM i to accept TN3270 as well as TN5250.

That said, people confusing 5250 for 3270 is more common than people actually using 3270 with an AS/400, so this is probably a case of the former rather than the later

State Farm?

Yes

> This forced greater changes in the UI compared to the other ports, because a lot of things which are easy to implement with character mode terminals are essentially impossible in 3270.

Couldn't they just render everything to a local virtual terminal and then send the screen after updates?

One big problem – on a character mode terminal such as a VT100, the host gets sent every single keystroke. So any key combination can be used as an "action key" – such as the slash key (/) used to open the Lotus 1-2-3 menu system. By contrast, on block mode terminals such as 3270, only a restricted subset of keys – such as ENTER and function keys – triggered a message being sent to the host, the rest of the keys were interpreted locally only. (Was there some mechanism to allow the host to redefine an arbitrary key as an action key? Not that I know of.)

How did Lotus 1-2-3/M address this? From what I understand, they adopted an approach commonly used in 3270 applications – a fixed area at the bottom of the screen was reserved as a "Command area". You would type your slash sequence there, and then press ENTER. The whole sequence would be sent to the host. If what you typed was not a full command, just the prefix of a command, I believe it would display you a menu showing the command options, similar to how 1-2-3 worked on other platforms.

But it also was a problem with things like scrolling off the screen. On 1-2-3 on other platforms, you could just use the cursor keys, and the screen would scroll immediately. Under 3270, the cursor keys are implemented locally, so you'd have to use a function key or command to scroll instead.

The speeds to terminals were not great, and this is completely in contrast to how the terminals were meant to be used.

The big idea behind the 3270 architecture was to support things like CICS, where you could have tens of thousands of terminals attached to a single processor computer with 16 megabytes of memory, and then take individual requests from terminals, recover state, and render screens.

SAS has a mainframe spreadsheet module.