By no means a complete list, but simply a way of grouping modems/routers (in no particular order):
Class I – early/older Conexant based routers
These routers all use the same Conexant Chipset and can use the same type of firmware.
OS: Wind river’s VxWorks (proprietary) – http://www.windriver.com
Manufacturers: Origo, Billion, Amigo, Telewell, Safecom etc.
Models: ASR8000, ASR8100, ASR8400 / SAMR-4110, SAMR-4114
AWR-7210, AWR-7214 / SWAMR-5110, SWAMR-5114, AWR-8210 etc.
Class II – TI Chipset routers
Routers that all use the same (Texas Instruments) TI AR7WRD platform and can use the same type of firmware.
OS: Linux (Open-source typically (MontaVista Linux)), Zyxel use closed source OS called Zynos
Manufacturers: Castlenet, Safecom, Netcomm, Zyxel, ASUS, Acorp, etc.
Models: Safecom SWAMR-54108/SWAMR-54125, SWART2-54125/GWART2-54125, Castlenet ASW800, Netcomm NB5PLUS4W, Zyxel P662HW, ASUS TI4631 etc. Other models include SART2-4112/GART2-4112, SART2-4115/GART2-4115, Acorp W400G
Some routers such as the SART2-4112/GART2-4112 and SART2-4115/GART2-4115 have less memory (2MB FlashRAM and 8MB RAM) than the other Class II routers. Routers like these may find some firmwares too large.
More:
https://www.routertech.org/faq/firmware/compatible-routers/
Class III – Alcatel (Thompson) xDSL controller
Alcatel routers tend to be able to tolerate a low SNR on the phone line.
OS:
Manufacturers: Speedtouch, Mentor, Connectplay & SAR (Solwise)
Models: Speed Touch 350, MTB-20152-EB
More:
http://www.modem-help.com/mfcs.php?mid=138
http://www.modem-help.com/mfcs.php?mid=138&nid=9915
Class IV – Globespan/Virata Chipset
Globespan have merged with Conexant, but prior to the merge they produced their own chipset upon which several modems/routers were based.
OS:
Manufacturers: SAR (Solwise), BT, Gentek
Models: SAR715, Gentek BB0060, BT Voyager 2000 etc
More:
http://www.modem-help.com/chipsets.php?mid=155
http://www.solwise.co.uk/adsl-sar715.htm
http://www.adslguide.org.uk/hardware/reviews/2003/q3/bt-2000.asp
Class V – ARM9-based network processor
(ADSL Modem: ST20166 & ST20174, Router: Samsung 2510, Wireless: TI TNETW1130)
These types of routers seemed to be most widely available after Class I and before Class II and are usually only wireless with a print server.
OS:
Manufacturers: Safecom
Models: SWAMRU-54108, GWAMRU-54108G
Notes
Ebuyer have on several occasions sold Safecom or Origo equipment under the “Ebuyer/Ebuyer Value” brand name.
The class numbering is not an industry standard and is merely an easy way for us at RouterTech to distinguish between different types of router.