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10:09
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A: Why did 1990s-2000s LCD all use 60 Hz refresh?

JustmeTo be fair, cost, need, and usefulness of anything above the standardized 60 Hz minimum for different resolutions are the reasons why it took long for LCD monitors to go past 60 Hz. The LCD panels were slow, compare that to a CRT with long decay phosphors. The settling time of new pixel value was...

Truth to that. But overdrive TN+ panels were way faster than early IPS. So how and why did 60 Hz get standardized and basically forced on everyone?
'Forced' seems a strong word, when standardization has benefits to both sides of an interface.
@Therac What would a user be benefit from a faster refresh rate? It would just cost more for user as you need also higher end video card that can do higher Hz video resolutions, and cost more to manufacturers so they get less profit. Most consumers had CRTs in 1990-2000 and office use only required a stable picture that does not flicker so 60 Hz was cheap and good enough. In 1990-2000 era, as a home or office user, why would you spend more money on a LCD with 75 Hz when there is nothing to gain, it might just result into slightly blurrier picture as pixels are sent faster.
@Therac Modern 60 Hz LCD panels still can't truly catch up to a 60 Hz CRT. No matter which LCD technology you used, you sacrificed something compared to a CRT. It's hard to believe if you don't have a CRT to compare to. The recent move to 120 and 144 Hz doesn't have much to do with human perception and a lot to do with the simple fact that even the most modern 60 Hz LCDs can't actually change the whole image 60 times a second. The 60 Hz figure only comes from the rate of the signal coming on the VGA cable. Not a big deal for office applications, which is what LCDs were made for :)
It's not accurate that graphics cards weren't able to deliver content that would have been able to take advantage of the higher refresh rates. The 3D graphics boom started in the late 90s, and graphics cards made quick advances in capabilities. nVidia's first GeForce card was released in 1999, and it was capable of running recent games at 1024x768 (which was considered a good gaming resolution at the time) at over 80 fps. And gamers absolutely took advantage of that on CRTs that supported higher refresh rates. But LCDs weren't really used for gaming at all at that time.
10:09
@Elezar Exactly - first LCDs were unusable for games even at 60 Hz so no benefit supporting higher refresh rates really. And CRTs could benefit from higher refresh rates such as 75 Hz and a VSYNC locked game could run stable at e.g. half of the rate at 35 FPS to prevent tearing or judder if it can't do 75 FPS on the system. That is slightly better than running on 60 Hz and 30 FPS.
None of that answers why exactly 60 though? Why not 50? 55? There were quite a few LCDs that did 75. What's special about that 60 number?
@Mavrik It comes from the TV era where refresh rate was locked to mains frequency, the big market for screens already evolved around 60 Hz signals and CRTs so when computers took off the monitors were made from existing CRT technology that already worked on 60 Hz. And yes TVs were 50 Hz on countries with 50 Hz mains. So computing devices did output 60 Hz already. When video resolutions grew the screen still had to be refreshed at the minimum 60 Hz rate so it did not cause eye strain as the CRT phosphors were made for 60 Hz, and highest resolution was always limited to 60 Hz.
@Justme The cost argument goes both ways; there are usually "cost first" products that cut the specs down, as well as premium hardware. Resolution, brightness, contrast, speed, even color depth could be 6-bit, 8-bit, or 10-bit. All except the refresh rate, which strangely was almost always 60, rarely 75 Hz (and 75 Hz wasn't a mark of premium models). So I wonder if there was something deeper behind this.
@Therac What if you really only had 60 Hz LCD panels, 60 Hz scaler chips, and video ADCs with pixel clocks that only supported maximum resolution at 60 Hz due to pixel clock limit? Even if you did have 75 Hz LCD monitor, how would it have a better picture under typical use? Remember that era had only analog VGA connectors. You barely had 8-bit per color component out from PC, and panels had max 8 bits per component, typically 6-bit, with temporal dithering. Just wondering, how would a office or home user see any difference or improvement between 60 Hz and 75 Hz format on an LCD? None?
@Justme That is my guess - that no one made e.g. 100 Hz monitors, because they couldn't buy 100 Hz parts. I'm trying to figure out which parts were the problem. As for the difference, there is some, but you usually have to nearly double the refresh rate to have it obvious. There was a number 75 Hz monitors, but they were not even marketed as faster. A user would see slightly smoother scrolling and less stutter in games when frames got skipped.
10:09
A display card which is outputting at a 70Hz frame rate will leave less video memory bandwidth available to the CPU than one which is outputting 60Hz. Unless the CPU and memory are fast enough to redraw the screen more than 60 times per second, pushing frame rates beyond that would slow things down rather than speed them up.
@Justme only 50Hz TVs are "locked" to the mains frequency. 60Hz TVs are not, on purpose, as the mains frequency is 60Hz, but the (color) TV frequency is actually 59.94Hz, specifically to be different than the mains frequency.
@RememberMonica Not correct. 50 Hz color TVs are also not locked to mains frequency because just like on 60 Hz color TV, the color carrier and sync signals need to have a defined relationship that can't drift and carrier has about 1 ppm tolerance, while e.g. UK mains allows 1% or 10000 ppm tolerance on mains and US 0.5% or 5000 ppm. The fact why NTSC is specified to be exactly 60/1.001 Hz is not because it has to be different from mains, but for other technical, regulatory and political reasons related to least interference between audio carrier, colour carrier, and horizontal sync frequency.
@Therac I don't think a normal person would see difference or find website scrolling at 60 Hz to be much worse than 75 Hz - most people have laptops or LCD monitors with 60 Hz only and I have not heard much complaints. As for games, they would generally ask for a specific mode so it could be 60 Hz mode even if desktop is 75 Hz. The games (in 2000s) could be designed to run at 60 Hz only and if they can render frames at 60 or 30 FPS but not at 75 or 37.5 FPS then you could have constant 25 FPS or more judder - think of 3:2 pulldown to fit 24 FPS movies to NTSC TV with 60 fields per second.
@Justme Most people won't complain about a 10-year old laptop, as long as it looks too shiny and new for them to tell, but that doesn't stop the market of big overclocked GPU and half-kilowatt CPU. 2000s games were mostly designed to run at any framerate, only some consoles titles got locked to 30 or 60. Most of this time, CRT monitors coexisted with LCD, mostly as a low-cost option.
The first sentence of your answer appears to be missing a verb, I cannot parse it
@Justme I've played lots of games and 60-fps-only ones just weren't a thing. No such games existed apart from crude console ports - some were so crude they only supported 30 fps. Every PC game, or every game that at least got a brief code review before recompiling for PC, supported any refresh rate available. As for 75 fps, that did exist! Which is even more surprising. But 80, 90 or 100 didn't. In the 2010s we got a lot of 120 and 144 Hz displays; the latter rate is a limitation of DVI.
10:09
@Justme The claim that it is locked was your incorrect claim, not mine. Note the quotes around "locked". The point is that 50Hz TVs are nominally 50Hz, but there are no nominally 60Hz TVs. Tolerances are irrelevant for the discussion - TV sets are 50Hz or ~59.94Hz, not 60Hz.
@supercat the "will leave less video bandwidth available" is incorrect, as a lot of video cards of that era had dual ported ram, with independent read ports for video refresh. It is probably true for most cards of that era, though.
@RememberMonica: US Television sets were designed to operate at 60Hz +/- a tolerance range that was sufficiently large as to make the change from the 60Hz black and white standard to the 59.94Hz color standard that for some reason persists today, irrelevant from a design perspective.
@RememberMonica There are. US TV black&white broadcasts were locked to 60 Hz mains and due to colour TV broadcast signals were changed to be atomic clock locked 59.94 Hz so not mains locked any more. Same with 50 Hz TV broadcasts. TVs don't really care what it is being fed as long as it is within some sane tolerance it can lock on. For instance an European C64 sends 50.12 Hz or so as it's 288p, not 575i. Modern digital TVs must advertize 60.00 Hz formats and must accept 59.94 Hz within tolerance, so they are nominally 60 Hz or both really.

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