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QUESTION -
. Were there computers whose text in text-mode, touched( or came close to ) the overscan border, and could this sometimes result in some of the computer-generated-display not being visible on some tv's / monitors? ?

Time range - Approximately 1975 - 1985, although any earlier examples are also interesting .

In late 70's and early eighties, on some tv's, you strongly felt as if you were not seeing all of the picture being transmitted, due to
1 - Curved corners of the screen ( variation on different tv's )
2 - Different screen sizes or ratios
3 - Or, because adjustment controls seemed to result in losing horizontal picture to gain vertical picture, or, vice versa.

Note - I don't know how curved corners worked on tv's or monitors, if or not tv-camera-sensors had curved corners, and if any computers had them in their video-memory ( I'm sure they did not ) .

Note - I'm thinking if the following thread -
Was the picture area of a CRT a parallelogram (instead of a true rectangle)?
was not deemed irrelevant, then neither should this one .

UPDATE
- All excellent answers etc, although I'm surprised no one has mentioned earlier computers ( maybe they were only kits ) from lets say 75-79 ( or earlier ! ), which seemed to display things right to the top or bottom edges of the screen, a display that looked like the famlous tv-typewriter .

UPDATE - I have now updated this question, even though the answers already received cleared up a lot of what I was curious about .

closed as too broad by Raffzahn, manassehkatz, Leo B., RETRAC, wizzwizz4 Mar 31 at 13:53

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    This is all about the TV technology and device setup, and in no way related to Computers. There is no feedback and the picture generating machine has no influence how the connected TV is configured, thus there is no relation to RC.SE. Pointing to an already borderline question to push it down a bit further the slipery slop isn't any helpful either. – Raffzahn Mar 29 at 22:09
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    All personal computers with video output designed to be displayed on TV have (at least by default) a sufficient border to compensate for any reasonable overscan that a TV might have. This is necessary so text and other important information doesn't get cut off. The includes modern PCs, where video cards will output a border by default when they think they're connected to a TV. This because most modern TVs still normally have an overscan area (again by default). At some point video consoles, like the PlayStation started using minimal borders, such that you wouldn't normally see them on TVs. – Ross Ridge Mar 29 at 22:24
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    @Raffzahn I think we disagree on where to draw the line but agree the current question is over the line. Vtc – manassehkatz Mar 29 at 22:50
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    @manassehkatz I can live with that. We all have different positions here, and that's not a bad thing either (Also, on a sidenote, an OT question can still be an interesting one - just not fitting for this site) – Raffzahn Mar 29 at 22:55
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    @traal Overscan is an attribute of the display. It's the part input signal that's not displayed because it would otherwise appear outside boundaries of the display. The borders that computers generates to prevent the main display area being cut off by the display are sometimes called overscan areas, because they're meant to be a part of the signal that is discarded because of the display's overscan. – Ross Ridge Mar 29 at 23:36
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1985 means we can include the Commodore Amiga, which was designed to display images beyond the visible screen area. Along with its genlocking capability, this feature made the Amiga attractive for video production.

The Amiga's standard Workbench resolution of 640x200 (NTSC) or 640x256 (PAL) just fitted inside the visible area of most TVs, but applications could open 'custom' screens which were wider and/or taller. A screen could also be pulled down to reveal other screens 'behind' it, and then the bottom of the 'front' screen would move down into the overscan area. Workbench included a 'Preferences' tool for centering screens on the user's TV or monitor. Later versions of AmigaOS also allowed the user to adjust the Workbench screen size to suit their tastes.

The photo below shows the 'high resolution' 640x256 pixel 4 color Workbench screen pulled down to reveal a paint program running in its own 'low resolution' 352x266 pixel 32 color 'custom' screen. The paint program's toolbar is partially hidden behind the tube fascia, so half the tool icons are invisible!

enter image description here

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    The picture shows clearly that the screen is capable of handling it ans all it needs is adjusting the picture - something that has to be done with each and every CRT based display in setup for a given signal. So no display cut off due any computer side signal, but missing setup for the signal produced. – Raffzahn Mar 30 at 8:03
  • all excellent answers etc, although I'm surprised no one has mentioned earlier computers ( maybe they were only kits ) from lets say 75-79 ( or earlier ! ), which seemed to display things right to the edges of the screen, a display that looked like the famlous tv-typewriter (a kit, p.s, if any arithmetic happened in the circuitry of this machine, maybe it could be defined as a computer, but I assume it did not ) – questiontype Mar 30 at 18:20
  • @questiontype Because the issue is the same for all: With a valid signal, positioning on the screen is an issue of the CRTs adjustment, not the computer. So if you see pictures using the screen way into the edge, it's because the user has adjusted the screen to show it that way, not because the computer did so. – Raffzahn Mar 30 at 22:04
  • @Raffzahn: Many/most TVs did not have knobs for CRT adjustment (at least not the ones i had). – Bjarke Mar 31 at 1:38
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    @BruceAbbott To bad I can't see the photo you mentioned. Now, what consists a user adjustable 'knob' is of course a good topic for some beer and a lengthy discussion. To me it includes everything that can be accessed without opening any screw or tight lock. So if the potentiometer to adjust is mounted at a PCB edge and the cover has a purpose build hole to adjust it, it's user adjustable (like with the 1996 Philips TV I got next door). Heck, it even got according symbols in its plastic cover to help finding the right one without a manual. – Raffzahn Mar 31 at 10:57
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Before computers, television broadcasts defined a "title safe" (or "safe title") area which was a rectangular region in the center of the video signal that any properly maintained television was guaranteed to display. Any words on the screen (titles) should fit within this area which occupies the center 80% of the screen, giving a 10% border all around.

A slightly larger area was the "action safe" (or "safe action") area where a properly maintained television would cut off the image. This area occupied the center 90% of the signal, giving a 5% border. A properly maintained television could display all or none of this area. Only the title safe area was guaranteed to be visible.

You asked whether there were any "computers that did not limit their display to a box centered in the middle of the screen". I think you are referring to the title safe area, and the answer is yes. The Commodore 64 and other computers could set the color of the border outside of the title safe area and could display sprites in this area. The NES went a step further by displaying a 256×240 pixel picture that covered the whole action safe area, and within that the center 224×192 pixels were considered to be title safe."

Computers used for full screen video production such as the Commodore Amiga (1985) also needed to be able to write to the entire action safe area. See Bruce Abbott's answer for more information.

So two use cases for this ability were (1) games, and (2) video.

In place of analog electron guns that had to be adjusted to keep the picture centered and sized correctly, today's digital displays have hardware pixels that go right up to the viewable edge of the screen and so the entire video signal is both action safe and title safe.

  • Or, back in 1980, the C64's predecessor the Vic20 had entirely flexible definitions for the border/display areas - one area where it was arguably superior to the C64. – JasonD Mar 30 at 11:46
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No.

A generated video signal will always be within the limits on the appropriate screen. If not, it will be due a misaligned (*1) display - or using a non fitting display, which is the same.

Keep in mind, especially when including monitors (that is devices not tied to any TV standard), there are no limits other than the ones set by its manufacturer. Any combination of line length, lines per frame and frames per second is possible. There is no right or wrong.

<Background_Information>

Common for all of these, the (composite) video signal for each line follows the same definition of Front Porch, Sync, Back Porch and Display Area as this nice picture shows:

Structure of a vide line (Taken from Wikipedia)

The Display Area is the part of the signal that is meant for display. It is fixed within the appropriate production line. For US TV production (60 Hz 525 lines) it's 52.6 µs, for European 50Hz/625 lines it's 52 µs. Anything longer will result in an invalid picture, everything shorter needs to be filled up (*2).

Early (hobby) machines often used the whole display area, leading to a picture creeping deep into the edges (*3) Later (home-) computers used in most cases only a section of the display area due various reasons (*4). The remainder was usually filled with their background colour (like white on a ZX81) or even offered to select a certain colour/brightness (think VC20).

Computers always outputed the whole area. It was up to the user to adjust the TV set in a way to emphase on the variable content or not.

Later the ability to cover the whole display area with more than just a border was sold as a 'new/additional' feature - more of a marketing move ignoring the past than anything really new.

</Background_Information>

So in any case, the display area of a composite signal is always the same and intended to be fully displayed. What part of the signal is finally shown is not determinated by the computer or it's video hardware, thus it can't be influenced by either. it's strictly an issue of (faulty) display setup.

Bottom line: The question is not about computing but display properties and a faulty setup thereof.


Note: The issue of Title Safe and Action Safe area are sometimes mentioned in this context (likewise Overscan, Underscan or Fullscan). Except, they are neither part of any of TV/CRT technology or relevant for a correct adjusted display. They are purely hints for TV producers where to place which content, to increase the chance that a transmission gets show even on malaligned TV sets. There is no guarantee for either to be helpful or to matter at all. For a computer setup a correct adjusted screen is default (and mandatory).


*1 - Or on purpose aligned that way. So if you see pictures using the screen way into the edge, it's because the user has adjusted the screen to show it that way, not because the computer did so.

*2 - By default in black, but any other intensity/colour is valid as well.

*3 - Noteworthy the TV dazzler with producing the whole display area from memory data - a fact that made it quite useful and a defacto standard in late 1970s early 1980s TV production.

*4 - Beside the intention to produce a certain pixel ratio, more often than not it was the same as with TV: staying within an area even quite old TV and/or less than perfect aligned TV will show without the need to be adjusted. It's all about user experience, isn't it? And having to adjust the TV set is no considered a perfect one - no matter how habdly adjusted it already is.

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    I'm always happy to collect down votes, as it shows that I hit a nerve where people prefer opinion over fact. Still, it would be nice if these opinions would result in a comment, stating what exactly is worth a down vote, and why. So don't just down vote, make RC.SE a better place by pointing out issues worth to be mentioned. – Raffzahn Mar 30 at 22:01
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    I didn't downvote, but as you can see in e.g. Bruce Abotts answer, the Amiga was able to display images outside the visible area of the some TVs from back then. None of my old TVs had the ability to adjust the width/height of the picture. The fact that most TVs from back then did not show the entire picture, is the whole reason the Commodore 64 has its border. So the answer must be yes. (You could argue that most TVs from back then were misaligned, but i think that's a different discussion) – Bjarke Mar 31 at 1:41
  • @Bjarke Since you commented this twice, I start to wonder where you looked. There is no TV without. It's impossible to build one without the ability to adjust picture alignment. They may not be on the front anymore, but they are present and (comparably) easy accessible. And yes, that some did not show the whole picture is because they where misaligned - that's the whole point here (and a great source of income for TV repair). The Amiga's Video doesn't counter this - after all, it got no influence on the setup of a connected CRT. – Raffzahn Mar 31 at 9:19
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    My TVs were probably from around the 1988-1994 era. I'm pretty sure i tried all the knobs - and i don't think my friends TVs could be adjusted in width/height either. (Monitors are a different beast - i remember that one of the cool "hi-tech" features of monitors were that their picture could be adjusted). I think the very first youtube result, when i searched for "crt picture adjustment", shows what i'm talking about - he has to open the back cover to adjust the picture: youtube.com/watch?v=9clJ-0LC8dw (So yeah, the feature is there but is hidden behind "Do not open!") – Bjarke Mar 31 at 13:17
  • UPDATE - I have now updated this question, even though the answers already received cleared up a lot of what I was curious about – questiontype Apr 2 at 21:42

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