Problem I: Unable to locate a driver for Citizen GSX140 printers (24-pin color DOT Matrix printer)
Solution: GSX 140 printers, as well as many other dot-matrix printers, actually emulate Epson printers. You can use the Epson LQ 2550 driver for the GSX140 and many other similar Citizen printer series. All features (including color printing) will still work.
Problem II: I can’t find the Epson LQ 2550 printer driver

Cause: Windows does not automatically include the driver and requires it to be obtained via. Windows Update.

Solution: Go to the Control Panel “Add Printer” wizard.
If you are installing a network printer, do not select “Use a Network Printer”.
Complete the installation as if you were going to install a local printer  on the LPT port (selecting any port at this stage is fine).
When you reach the driver selection screen, press the “Windows Update” button. Window will begin downloading hundreds of legacy drivers — included is the Epson LQ 2550. This will take awhile on slower connections and cannot be paused or stopped.
If you were installing the printer as LPT or as USB with an LPT converter, you can continue. If you were meaning to install a Network Printer, cancel the wizard  and start it again for network printers. You can now select the LQ 2550 driver under “Epson” manufacturer printers.

An alternative is to use the Epson LQ Series 2 (136) driver, but this will only support 180×180 printing in black and white.

Reworded: For Citizen GSX 140 series Printers, use the Epson LQ 2550 driver.
If you need the Epson LQ 2550 driver, but it is not available, use the Epson LQ Series 2 (136) driver which will not support high resolution or color (also works for Citizen GSX 140)
Many other dot-matrix printers use the same drivers.

One important note! The LQ Series 2 (136) driver will not support color printing or high resolution printing. We are currently investigating as to why our trial run of this yielded only black & white printing which may have been from a variety of causes (wrong driver, our CUPS server, the Windows computer connected, etc).

Question: “Where can I find the Citizen GSX 140 printer manual?”

Answer:

Here: http://www.virtualizationadmin.com/files/whitepapers/ultimate_printer_manual/printers/mczg14.htm

Image via Wikipedia

Most printer paper is 8.5×11″. (Thats inches…)
Or 216 x 279 mm

The name for this standard is “A (letter)”.

Other paper sizes:

(Chart Source: Wikipedia)

A ridiculous amount of information about paper sizes can be found here:
http://en.wikipedia.org/wiki/Paper_size

And another chart with more sizes can be found here:
http://www.dpandi.com/paper/index.html