PS1:PS1 Model Differences
Page content & researching collaboratively taken from io55.net's PS1 page with permission.
There are three PS1 models, with one of these models having five revisions.
Models + Revisions
Models are arranged chronologically. Revisions are underneath their respective model.
“PlayStation (original)” (1995-2000)
The instantly recognizable “fat” gray console. Various revisions exist within this version, all of which change something about the consoles I/O or internals. Up front is 2 controller ports and 2 memory card ports. On the top is the CD drive, and buttons for power/reset/opening the drive. To the back is the aforementioned I/O, which always has AC power, multi video out, and serial I/O. Older revisions will have direct RCA + RFU out and/or parallel I/O. Furthermore, some older revisions have technical and graphical issues or inferiority. Reliability is mixed across all revisions, with some faring worse than others. This version is the most commonly model found for the PlayStation.
The first PlayStation, possessing the most ports; direct RCA + RFU in addition to parallel/serial/etc. Alongside that, the DVD tray has the laser/”black” area up top, instead of to the right. Due to a poor CD drive laser, these consoles experience FMV and music skipping in games at a notorious level. Paradoxically, the DAC in these systems made them favorable for music CD playback, supposedly par with the best CD players of their era, not ours (202X). However, these systems use outdated VRAM, resulting in lower (5-bit) shading + worse transparency blending. This leads to both slowdowns (transparency) and color banding (shading). In essence, this system's high point is the direct RCA/RFU + high quality DAC.
Here, the direct RCA and RFU have been removed from the console (still possible to attain RCA with a multi out to RCA cable). The DAC has been downgraded, but the VRAM was upgraded to SGRAM, allowing the console to support 8-bit shading, in addition to swifter transparency calculations and full screen dithering. Lastly, the drive lasers have been improved somewhat, eliminating the notorious level of skipping found in the 1001. As with all PS1s, however, the drives still can have their issues, just not as badly as the 1001. Some claim these have the highest quality video output, but this is unverified and needs investigation. Note: SCPH-5001 does not appear to have been manufactured at any point, and thus it has been excluded.
Included for it’s especially interesting featureset, even if it's an NTSC-J revision. Exclusive to southeast Asian markets, this revision has reintroduced the direct RCA and RFU, while also adding Video CD support (which was originally planned worldwide). These also use the revised board which contains SGRAM over VRAM, and potentially the better laser. The quality of their DAC is unknown.
These systems contain a smaller and more efficient motherboard with less chips, which impacts the user if they are interested in hardware modding. Since the CD DSP is now merged with another CD chip, installing the xStation drive emulator has been rendered impossible, except for certain early 7000s with a PU-18 motherboard. However, one can still install the PS1O drive emulator despite this change. These systems also have a music visualizer, and were the first systems to be bundled with the DualShock controllers. Some claim these have the best and clearest video output, in direct opposition to the 5501. That, like the 5501's claim, is equally unverifiable and needs investigation.
These systems have continued the trend of shrinking the motherboard and reducing the chips, with a more immediate detriment to user. Alongside not supporting the xStation, these consoles do not have a parallel port (or simply no cutout for it). Simultaneously, they don’t bring any upgrades to the table, for either the laser or the hardware. It is important to note that some earlier 9001s actually have the parallel port on the motherboard, but it is covered up by the console’s case. Later 9001s do not even have a hidden parallel port, however. This lack of the visible parallel port makes using the PS10 either very difficult or impossible.
“Net Yaroze” (1997-2000?)
A slightly different variant of the standard PS1, intended for indie developers and hobbyists. Despite this status, almost nothing is changed in the console’s hardware, although it is black in color. The only meaningful changes are the lack of region lockout & the different boot ROM. Everything else of note relates to the extras the system shipped with. The one other upside is that the Yaroze has direct RCA + RFU out, whilst also seemingly containing the superior SGRAM (possibly the better laser too, some disagree). This makes the Yaroze the only consumer-level PS1 that has both the direct RCA out and the SGRAM.
“PS one” (2000-2006)
A cost-reduced and shrunken version of the PS1, colored in white with a rounded design. About as common as the "fat" PS1. The I/O of this console is even more reduced than the last revisions of the "fat", as the PS one does not even have an accessible serial port or a reset button. However, significant modding allows re-adding the serial port to the PS one system. Lastly, the PS ones appear to have some of the best reliability compared to earlier models.
http://www.psxdev.net/forum/viewtopic.php?t=365 (ps one serial mod)
https://segaretro.org/Sega_Saturn/Hardware_comparison#Revised_PlayStation (SGRAM again)