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The cursor used on my 486 (and Pentium 3) in MS-DOS 6/7 has a thick underlined character. I cannot find that in code page 437. The underscore character is the closest to it, but is thinner.
Where does this cursor character come from? Or did I miss something?
The text-mode cursor isn’t a character, it’s managed separately by the video output circuitry (which is how it keeps blinking even when your computer is busy or locked up). It can be enabled or disabled, and its size can be determined — at least, its start and end scanlines, which determine its height; the cursor always occupies the full width of a character cell. That way you can have the simple cursor beneath your text, the half-cell cursor typically used for insert mode, a full-cell cursor, etc. Even a cursor above your text if you want! On EGA, and many VGA clones, you can also have a split cursor: if the end line is above the start line, you end up with a two-part cursor with lines at the top (down to the end line) and at the bottom (from the start line).
The OSDev Wiki has more information on the topic, including pointers to the BIOS functions you can use, and code to directly manipulate the VGA registers (the cursor is also available on MDA, Hercules, CGA and EGA obviously). FreeVGA is also relevant (amongst many other resources on the topic).
Emulating IBM PC Cursors illustrates the various effects and provides an in-browser emulator running PC Magazine’s CTYPE so you can try different settings directly. (Thanks to Michael Kjörling for the suggestion!)
The cursor on the CGA, MDA, EGA, and VGA cards was a hardware sprite generated on the earlier cards by the 6845 video controller, and on later cards by a chip that emulates the 6845. That chip has an address counter that is used to fetch data from memory, as well as a line counter and a cursor-state latch. It also has a programmable registers for cursor address, cursor start line, cursor end line, and blink pattern.
Every time the display controller advances to line N of a character row, it compares N against the cursor-start and cursor-end registers. If it matches the former, it sets the cursor-state latch; if it matches the latter, it clears the latch. At all other times, the latch keeps its state. If the cursor is programmed to be active in rows 10-13 of each character, this signal will be active while drawing rows 10-13 of every character line.
Any time this latch is set, the value in an internal 5-bit frame counter matches the requirements of the blink pattern, and the display is fetching data from the programmed cursor address, the 6845 chip will output a "cursor" signal. The CGA and MDA will then filter this signal with a redundant (worse than useless) blink circuit. Whenever the filtered signal is high, the CGA or MDA will ignore the bit pattern of the character being displayed and unconditionally display the foreground color. The cursor has no effect upon anything stored in memory, and because of the CGA's redundant blink circuit there's not even any way for software to tell whether it's visible at any moment in time.
Its been a very long time since I used MSDOS but on most video cards it flashed, that is it put down a _for several refresh cycles of the video page, and then a dim rectangle ▒ for several refresh cycles. so it looked like the character block was flashing on and off. This could actually be changed. As I recall you had to put lines in config.sys or Autoexec.bat.
I remember one mod people did was change to a little smiley face rather than the rectangle, like this ☺ but a square rather than round smiley.
You could use any character in the ascii dingbats see image(Note square smiley is second character.) and link bellow for wikipeidia.
https://en.wikipedia.org/wiki/Code_page_437
Note it was latter MSDOS versions(I think 3.0+.) that added ascii dingbats.
