Browsing around eBay, I noticed that some TI-81s have a screen that is off-white and have bluish-gray pixels, while others have the standard STN screen like a TI-82. Did TI change the screen type?

http://mycalcdb.free.fr/main.php?l=0&id=1842
 vs
http://www.partlancer.com/pics/TI-81-Graphing-Calculator-WORKS-FOR-SCHOOL-LOOK.JPG.jpg

My understanding from talking with people like Ben Moody, Randy Compton, and Michael Vincent is that some TI-81 units did indeed have a different LCD. I think some of the earliest ones had the high-contrast bluish ones like the 82 and 85, but most of them (like my ROM 2.0V one) had the grayish, poor-contrast version with only ten contrast settings instead of 32. Not sure why they would switch to a worse version unless it was due to cost.

Interestingly, the interface with the LCD changed on some models, too. Apparently early TI-81s had a memory-mapped display like the TI-85 and 86, while the later ones (2.0V and above?) reverted to an 82-style display driver and hacked in an interrupt routine to periodically copy the entire display to the driver. This often results in an odd, slow, flickery effect when running programs that rapidly clear and display text on the screen on these units.

Perhaps they switched back and forth once or twice, since yours (1.1K or something, IIRC?) and mine (2.0V) have gray LCDs, but I think Randy said his 1.8K model had the blue one.

As for Disp speed, the models with memory-mapped displays would certainly appear faster (or at least, less choppy). I'm not sure if this alone could account for actual speed in terms of lines printed per second, unless the slow copy-to-driver interrupt routine consumes enough time to noticeably slow down everything else (which it may or may not, I don't know).

I found clearer pics of TI-81 screens on Datamath via web archive. Those show a change in screen starting in ~1995, consistent with below. However, there were only two at the time.

Based on comparison, I noticed the following trend, listed in order of appearance on the current Datamath page:
The ES cannot be determined, appears blue
The second appears to have a blue screen
The third has a blue screen
The fourth has a gray screen
The fifth has a gray screen

Seems they reduced quality then. For cost reasons they probably put in a lower-quality screen in the very first ones to see how well it performed in the market (?). That's just my guess.

eBay also makes a good photo repository IMO.

Looking closer, it seems the gray screens are more pixely than the blue screens. That means only the third one used a blue screen, which seems correct. I should look before I post .

I have a TI-81 around my house somewhere. It was used maybe a little to heavily until it's unfortunate demise in the -45˚C(-50˚F) weather in Alaska. It had bluish pixels though.

(hopefully acceptable necrodoublepost) After browsing through several hundred eBay listings, they were all manufactured between mid 1992 and early 1993, with hardware B. It also includes ViewScreen models, but I am unsure about the attached screen. I also noticed that the first-generation TI-81s without backup batteries are quite common.

TI did switch the hardware around a lot on the 81. I have a later TI-81 (2.0V, hardware revision F) and it doesn't have the memory-mapped screen. I've taken pictures of partial characters on the screen, mid-refresh.