NES:NES Model Differences
Page content & researching collaboratively taken from io55.net's NES page with permission.
There are two NES models, and three minor/internal revisions for both of the models.
Models + Revisions
Models are arranged chronologically. Revisions are underneath their respective model.
NES-001 "Front-Loader" (1985-1993)
The distinctive and iconic original version of the NES, with it’s instantly recognizable grey and black color scheme + square controller. Often called the “toaster”. Loads cartridges from the front, using a mechanism that is quite prone to failure. Video output is through either a composite or RF port, resulting in superior quality (when using composite). On the bottom is an unused expansion port. Region locked and bootleg game locked without workarounds (within console or cartridge). Has a channel 3/4 switch above the RF out port. CPU, PPU, and RAM variants may impact game compatibility.
NES-001 (PCB rev. -01 to -04) (1985-1986)
May have video quality that is poorer than expected for the NES-001. Some of these, especially the early ones, may be prone to frequent errors and unreliable behavior.
NES-001 (PCB rev. -05 to -09) (1986-1989?/??)
Both the video quality and behavior issues from the first revision have been removed.
NES-001 (PCB rev. -10 and -11) (1987-1993)
While the video quality and reliability issues have not returned, these consoles have more safeguards included against cartridges attempting to circumvent the lockout chip.
NES-101 (New-Style; top-loader) (1993-1995)
Much smaller than the 001, with a primarily white and rounded scheme + dog bone controller. Cartridges are loaded from the top, using a much more reliable mechanism. Video output has been reduced to only RF out, resulting in significantly worse quality and higher levels of interference (this can be modded out). The expansion port seems to be removed. The lockout chip is removed, making this console region free and easier with bootlegs. Less compatible with certain cheat cartridges and very few official games. No power LED, unlike the 001. Somewhat rarer than the 001, but still relatively cheap.
NES-101 (NESN-101 PCB) (1993-1995)
The typical feature set for the NES-101, with the poor RF out and such.
NES-101 (NESN-CPU-JIO-01 PCB) (1993?-1995?)
This rare revision drastically improves the shielding on the RF out, which eliminates the “jail bars” vertical interference typically seen on the NES-101. It may also generally improve output quality in ways that are not as distinctive as the vertical lines. These were only available as a replacement console from Nintendo, for people who complained about the normal NES-101’s video quality.
NES-101 (NESN-CPU-AV-01 PCB) (1993?-1995?)
In effect the ultimate NES-101 revision, the RF port has been completely axed, having been replaced by a normal composite AV out. While this model, like the JIO-01, was sent out by Nintendo to replace the originals of complaining customers, it was also sometimes found in American department or electronic stores, making it a bit less rare.
References
https://en.wikipedia.org/wiki/New-Style_NES
https://www.youtube.com/watch?v=DQ7hKoh9MCo (video quality, front vs. top)
https://retrogamebuyer.com/original-nes-vs-top-loader/
https://forums.nesdev.org/viewtopic.php?p=196688#p196688
https://gametrog.com/nintendo-entertainment-system-nes-information-specs/
http://nerdlypleasures.blogspot.com/2017/06/official-variations-of-nintendo-8-bit.html