Trixter
Veteran Member
For decades, I was under the impression that the viewable area of an IBM 5153 CGA monitor (and, possibly, all CGA monitors) was supposed to look like it was evenly spaced from all sides of the bezel, such that the overscan border was of an equal thickness on all sides. My own hardware has been configured like that for decades, and looks like this:
Further reinforcing my impression of this was the fact that DeluxePaint from the 1980s has built-in aspect ratio correction, which you could turn on and off as needed. I used it to create the following aspect ratio test picture, which displays a perfect circle/square with the monitor adjusted as shown directly above. That test picture looks like this:
(The wording in the left circle is incorrect, please ignore the wording for now)
However, it was recently brought to my attention that the designers may have intended the display aspect ratio to be 1.37, which is closer to NTSC than I would have expected. To match this, it means the correct adjustment of the viewable area would have very thin overscan borders on the top and bottom compared to the sides, like this:
(Again, note how there is almost no overscan on the bottom.)
Which is correct? I've checked the 5153 tech manual as well as the SAMS Computerfacts document and there is no mention of what the proper adjustment of the viewable area is supposed to be. I thought I could answer this question by grabbing samples of the 5153 from youtube videos, images, and old magazines in my collection, but after two hours I could only gather a decent sample size of 22 images (where the viewable area/overscan border were very clearly visible) and the results were inconclusive.
What did IBM's designers intend? What is the correct adjustment for viewable area and overscan on an IBM 5153 CGA monitor?
(I'm hoping this post brings some of the old monitor repair people out of the woodwork, as it's possible the only people who might know are those who directly serviced these monitors...)
Further reinforcing my impression of this was the fact that DeluxePaint from the 1980s has built-in aspect ratio correction, which you could turn on and off as needed. I used it to create the following aspect ratio test picture, which displays a perfect circle/square with the monitor adjusted as shown directly above. That test picture looks like this:
(The wording in the left circle is incorrect, please ignore the wording for now)
However, it was recently brought to my attention that the designers may have intended the display aspect ratio to be 1.37, which is closer to NTSC than I would have expected. To match this, it means the correct adjustment of the viewable area would have very thin overscan borders on the top and bottom compared to the sides, like this:
(Again, note how there is almost no overscan on the bottom.)
Which is correct? I've checked the 5153 tech manual as well as the SAMS Computerfacts document and there is no mention of what the proper adjustment of the viewable area is supposed to be. I thought I could answer this question by grabbing samples of the 5153 from youtube videos, images, and old magazines in my collection, but after two hours I could only gather a decent sample size of 22 images (where the viewable area/overscan border were very clearly visible) and the results were inconclusive.
What did IBM's designers intend? What is the correct adjustment for viewable area and overscan on an IBM 5153 CGA monitor?
(I'm hoping this post brings some of the old monitor repair people out of the woodwork, as it's possible the only people who might know are those who directly serviced these monitors...)