Regarding a recent discussion on the various aspect ratios available to the stock console (or emulations thereof), there seems to be some clarification needed on what the actual aspect ratios are of the original TI output (both 60Hz and 50Hz). I say "needed" because, firstly, this info is very hard to find, and, secondly, there is a belief among some that the TMS9918, at least, has a 4:3 aspect ratio addressable pixel area with square pixels. This is not true, and, consulting the datasheet to solidify the numbers in my own mind, it is clear that neither the TMS9918A nor the TMS9929A employ use of square pixels. Most of the emulators I've seen use square pixels. Hopefully these numbers will be of use to someone else at some point.
On page 5 of a document entitled TMS 9918A 9928A 9929A VDP Preliminary Specification 1981, there's this section:
The hasty handwritten figures aren't mine; that's how I found this document on the web, and boy, it is not an easy document to find. Here it is for posterity, and, from this datasheet, plus the F18A documentation here, I've put together a side-by-side comparison of the different aspect ratios offered by each VDP.
Remember that all of these are designed to send their output to a 4:3 screen. With the TI's addressable pixel area being 256x192, or also 4:3, you may think that this is a great match: 4:3 addressable area to a 4:3 screen = 4:3 aspect ratio. But no, the timings of the various analogue video systems have to be respected, so extra pixel rows and columns are required to border the addressable area. The 60 Hz VDP outputs an area of 284x243, although only 256x192 pixels are addressable, while the rest of the 'pixels' are set to a solid background colour. The 50 Hz VDP outputs an area of 284x294, although, again, only 256x192 pixels are addressable. Of course, there are no actual 'pixels' in the border area, but the pixel clock is running, nonetheless, and a pixel width is used as a reference in the above datasheet for the amount of vertical or horizontal space occupied by this area.
The F18A outputs square pixels, as asserted by the chip's designer. However, square pixels (1.333:1) are a slightly different 'squeeze' to what you'd get from an NTSC console (1.52:1), and very different to what you'd get from a 50 Hz console (1.82:1).
Given the numbers provided by the creators of all three products, the side-by-side comparison of aspect ratios looks like the following diagram:
Personally, I most prefer the NTSC shape. It's a nice fit for the available screen area. The 50 Hz (PAL) that I have access to I.R.L. is too squashed in the vertical direction (or "short"), while the F18A is too "tall" for my liking.
That being said, my previous sentence is merely my opinion, and not a slight on anyone nor any reason to take offense. I'm just stating a preference, and y'all are welcome to your own!
Also, please note that results may vary, depending on the knobs and settings on your old CRT. On some of them, you can adjust H-WIDTH, and even V-HEIGHT is often a possibility. Both of those will alter the aspect ratio by squeezing or stretching the image. LCDs do a better job of remaining faithful to the input signal and not chopping anything off, but, if you fiddle with the menus, you can usually override that as well, depending on the monitor.
If I've made any errors, please let me know!