CRT monitors, or Cathode Ray Tube monitors, are the ones that look like a television and are normally used with non-portable computer systems.

CRT monitors were the standard type of monitor for many years before being largely replaced by LCD and LED monitors. They are characterized by their bulky, box-like design and the presence of a cathode ray tube, which is a vacuum tube containing an electron gun and a fluorescent screen.

Here is some detailed information about CRT monitors:

1. Definition and Structure:
- CRT monitors work by using an electron gun to shoot a stream of electrons onto a phosphor-coated screen.
- The screen is divided into thousands of tiny pixels that can be illuminated by the electron beam, creating images and text.

2. Advantages:
- CRT monitors have excellent color reproduction and good contrast levels, making them suitable for tasks that require accurate color representation, such as graphic design or video editing.
- They have a high refresh rate, which means that they can display fast-moving images without motion blur.
- CRT monitors have a wide viewing angle, allowing users to view the screen from different positions without a significant loss in image quality.

3. Disadvantages:
- CRT monitors are heavy and bulky compared to modern flat panel monitors, making them less portable and taking up more desk space.
- They consume more power than LCD and LED monitors, leading to higher electricity bills.
- CRT monitors emit electromagnetic radiation and can cause eye strain over prolonged use.

4. Replacement by LCD and LED monitors:
- LCD (Liquid Crystal Display) and LED (Light Emitting Diode) monitors have become the standard in recent years due to their slim design, energy efficiency, and improved image quality.
- LCD monitors use liquid crystals to control the passage of light through the pixels, while LED monitors use light-emitting diodes for backlighting.
- These monitors offer higher resolutions, wider color gamut, and are more lightweight and portable compared to CRT monitors.

In conclusion, CRT monitors are the ones that resemble televisions and were commonly used with non-portable computer systems. However, they have been largely replaced by LCD and LED monitors due to their bulkiness and lower energy efficiency.