24 What is the EEPROM, EPROM, PROM on my video card?
Description
This article is from the comp.sys.ibm.pc.hardware.video Frequently Asked Questions, by Michael Scott with numerous contributions by others. (v1.0).
24 What is the EEPROM, EPROM, PROM on my video card?
A PROM (Programmable Read Only Memory) chip can be used to store video BIOS code and/or video configuration information. All modern video cards have a video BIOS, while many (but not all) store video configuration data right on the video card.
Usually, EPROM's or PROM's (the 'E' indicating that the PROM is erasable or 'reprogrammable') are used to store the video BIOS. The BIOS consists of code which the computer uses to communicate with the video card. Occasionally when a bug is discovered in the video BIOS of a card, the card manufacturer will supply updated ROM's that contain corrected video BIOS code. Swapping of the new chip for the old is quite easy and safe, as long as the machine is powered off and appropriate electrostatic precautions are taken.
EEPROM's (Electronically Erasable PROM's) are used on some video cards to store video mode configuration information. These cards usually require the user to run an installation program initially to determine the correct screen refresh rate for the monitor at each screen pixel addressibility used. Whenever the video card receives a request from the computer to switch video modes, the card checks its EEPROM so that it can generate the video signal at the correct vertical refresh rate. Information such as horizontal and vertical centering and size can also be stored by some cards.
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