NDS:Nintendo DS Model Differences
Page content & researching collaboratively taken from io55.net's Nintendo DS page with permission.
There are four Nintendo DS models.
Consumer Models
Models are arranged chronologically.
Nintendo DS [NTR-001] (2004-2006)
The “Classic” Nintendo DS, easily identified by it's “bulky” design with ridges on the outer shell, rectangular start/select/power buttons, microswitches (clicky buttons), a large D-pad, and speakers with many dots. Being Nintendo's first crack at the DS, and the only DS model to release somewhat in the 6th generation (complete with a GBA slot providing near 100% compatibility except for the lack of a serial port, and being falsely advertised as a "third pillar" that would not replace it), this model has a few small weaknesses compared to it's followup, the Lite. However, these weaknesses are minor - a shorter and thinner stylus, slightly lower battery life and darker screens compared to the Lite's minimum brightness. Otherwise, the original DS is a perfectly serviceable system that can hold it's place as a worthwhile device.
It shares the same EXT2 power socket as the GBA SP, and even its headphone adapter is supported despite all DSes having a standard 3.5mm headphone jack built in. Comparably, GBA SP and DS batteries are interchangeable if the plastic tabs on them are removed.
In its original packaging, it came with a second stylus and a wrist strap with a thumb pad alleged to facilitate stylus-free touchscreen operation.
The DS/Lite's touchscreen controller additionally supports pressure and temperature measurements (mainly used by homebrew, like "Colors"); finally, well before the TN vs IPS debates on handhelds designed to be used by one person looking straight-on at them, the first DS featured the original console display debate - "grid screen" versus "grain screen" touch panels.
Nintendo DS Lite [USG-001] (2006-2011?)
Despite being the 2nd version of the DS, the Lite is what most will think of when they recall the “Nintendo DS”. Wildly popular in sales figures, the DS Lite is a very common system.
Improved on the original DS by making the case sleeker, lengthening the stylus, increasing battery life, and making the screens brighter and more vibrant. Easily identified by its circular start and select buttons, two LEDs at the right of the hinge and the microphone in its center, a "short" GBA slot that leaves standard sized cards protruding, its sleeker “perfectly rectangular” design without shell ridges (only a logo), speakers with less holes, and a power slider on the system's side.
Nintendo DSi [TWL-001] (2008-2012?)
The half-generation update to the DS line.
Easily identified by its triple power/charge/internet LEDs on the left of the hinge, prominent front and rear cameras, an SD card slot, no GBA slot, power button below the D-pad, and a size comparable to the DS Lite but slimmer and squarer. On the inside it brought CPU/RAM/Wi-Fi upgrades and a Wii-like pseudo-operating-system architecture with a redesigned launcher and timid multimedia features, all stored on eMMC NAND on which further digital software could be installed from an online shop.
The DSi also received dedicated software, identifiable by the "TWL" product code on the ROM/card/box, which is required to take advantage of most of its innovations, including 802.11g/WPA wireless. A very modest amount of DSi exclusive physical releases even exist, which prominently have a DSi logo on the box/label artwork and a white shell. Most DSi software is region locked, however.
Again comparably to the Wii or PS2, DS/i software runs on the bare metal and once arbitrary code execution is achieved anything the host title could do becomes possible; unlike those consoles, permissions and other post-boot security on the DSi are not enforced by a kernel, but rather by hardware that is initialized in the boot chain and can be selectively disabled until the next reset. Between this, only one awkward and abandoned DSi-mode flashcard (the CycloDS iEvolution), and lots of scene drama and vaporware - the DSi modding scene was for most intents and purposes "a DS Lite with disadvantages" until 2018, which was marked by the release of a persistent all-access coldboot exploit (Unlaunch), then of a method of installing it without hardmod (Flipnote Lenny), then of another one not relying on optional software (Memory Pit), along with a new wave of DSi-enhanced or even exclusive homebrew.
Last but very far from least, the DSi replaced the analog volume control with up/down buttons providing 7 steps of adjustment, unless the Select button is also held down, in which case they operate as a 5-level backlight control (which returned to being an inferior menu-based adjustment on following Nintendo products).
Nintendo DSi XL [UTL-001] (2008-2012?)
Very similar to the DSi, for obvious reasons. At first glance, the DSi XL appears to simply be a larger version of the DSi. However, certain improvements over the original DSi make the XL a better system in several aspects. Most importantly, both of the screens on any DSi XL are guaranteed to be IPS screens, or in other words, guaranteed to have superior viewing angles, superior color reproduction, and superior brightness. Furthermore, the XL has slightly better hinges (can lock at a 120 degree angle), generally longer battery life (a few more hours over the DSi), and louder speakers with better enclosures.
Nintendo Zone Boxes
Special purpose, but mostly ordinary apart from automatically switching on and off with external power, non-retail DS consoles designed for wall mounting.
Nintendo Zone Box [NIS-004]
A large plastic white box designed to resemble the DS Lite's logo. While the exact implementation is unknown, it contains a modified DS Lite (USG-001C) and a Slot-2 "Power Control Cartridge" (WDB-USZ, same as the Slot-1 cards with the actual distribution ROM) with a 2-pin connector on its back, which may or may not interact in providing an external power LED and automatic on/off with external power. Two flip-top covers provide access to the console's displays.
According to isolated mentions on the internet, the USG-001C may have been preceded by the USG-001A and the NTR-001C.
Nintendo Zone Box [NZB-001]
A highly modified DSi that only runs on external power (completely lacking a battery) and only has an upside down bottom screen with a folding hard cover; no buttons either.
References
https://en.wikipedia.org/wiki/Nintendo_DS
https://en.wikipedia.org/wiki/Nintendo_DSi
https://en.wikipedia.org/wiki/Nintendo_DS_Lite
https://shmups.system11.org/viewtopic.php?t=61686
https://www.neogaf.com/threads/why-dont-more-games-use-the-pressure-sensitivity-on-the-ds.385163