Googling around the Internet I found conflicting information or strange myths about these computers, so as owner of one of these PCs I see a need to sort them out.

BIOS
First (and the most frequently asked question) is if they do have a BIOS setup and what's the keystroke combo. Many places state they have (although nobody gives a key combination). At zimmers.net site you can even find supposed utility disk for 10/20-III series which contains setup.exe, but that's for PC40 (!). So once and for all:

Commodore PC10-III/20-III like many other XT clones doesn't have built-in BIOS setup program nor any other utility (in OS executable form) for this purpose.

However it's BIOS does have two simple utilities built-in:

COMMODORE 8088 Monitor which can be called using debug command:
G=F000:0

and

Western Digital IDE Superbios utility which can be called using debug command:
G=FA00:5

also there are two utils for DOS:
speed.exe which can be used to set CPU speed:
speed.exe -s - "Standard" 4.77MHz speed (same as pressing CTRL+ALT+S)
speed.exe -t - "Turbo" 7.16MHz speed (same as CTRL+ALT+T)
speed.exe -d - "Double" 9.54MHz speed (same as CTRL+ALT+D)

setclock.exe which can be used to set realtime clock based on system time and vice versa:
setclock.exe -r - sets system time based on realtime clock
setclock.exe -w - sets realtime clock based on system time

Jumper settings
Only two motherboard jumpers are documented in the manual.
JMP 208 - enables built-in XTA hard disk controller: enabled (jumper on pins 1-2 - position A) or disabled (jumper on pins 2-3 - position B)
JMP 614 - sets composite output mode: color (jumper in) or mono (jumper out)

however there are more jumpers that are described as factory set or not described at all - some of them do have jumper headers soldered in, some do not:

JMP 101 close = FE2010 (PC Bus and CPU peripheral controller) pin 16 set to GND. According to the data sheet, this pin is unused, Commodore has labeled the with NTSTCLR.
JMP 206 - HDD IRQ 5 ON/OFF
JMP 207 - HDD DRQ 3 ON/OFF
JMP 301 - it seems it's realtime clock CMOS clear jumper.
JMP 204/205 = U201 EPROM type:

• 27128: JMP 204 open / JMP 205 1-2
  27256: 204 JMP open / JMP 205 2-3
  27512: 204 JMP closed / JMP 205 2-3

PAD 201-203 = FD9268 FDD controller write precompensation preset
JMP 612 = PVC4 video chip data ON/OFF
JMP 611 = PVC4 video chip READY signal ON/OFF

Keyboard
These computers doesn't need any special, propertiary Commodore keyboard. Regular XT keyboard works just fine with them.

Resources (manuals, BIOS images, utilities and more):
http://vicerveza.homeunix.net/~viric/oldcomps … ore_pc10-3.html

https://ancientelectronics.wordpress.com/2015 … 0-iii-pc20-iii/

https://oldcomputer.info/pc/commodore20/index.htm

http://www.zimmers.net/anonftp/pub/cbm-pc/ALLFILES.html
http://www.zimmers.net/anonftp/pub/cbm-pc/doc … Information.txt - most complete source of information, beside the original manuals.