Pentuim 4's are slow, and very inefficient compared to modern desktop CPUs.

Claggy

... but I reject them manually.

#!/bin/bash
#Script to adapt BOINC's global CPU usage to CPU temperature
#Use your favorite internet search enginge
#for your CPU's suggested temperature
#Written for AMD Athlon 64 X2 (R) [2006]
#
#Released into the Public Domain or CC0, your choice.
#Thanks to grymoire.com, tldp.org, stackoverflow.com
#and all of the Open Source Community.

#Set target temperature of your CPU in Degree Celsius here:
TARGTEMP=50

#Set how often usage is changed and changes are put on screen in minutes
CHANGEPAUSE=1
OUTPUTPAUSE=15

#Simple check for dependencies
DEPENDENCIES="sensors sed"
for i in $DEPENDENCIES; do
if ! command -v "$i" >/dev/null
then echo "Please check if you have the package necessary for \033[1m$i\033[0m installed." && exit 1; fi; done

#Change to BOINC_DIR and create temporary folder for backup
BOINCDAT=$(grep BOINC_DIR /etc/default/boinc-client | grep -v "\#" | cut -d"\"" -f2)
cd $BOINCDAT
mkdir -p tmp

while [ -e "lockfile" ]; do
#Grab current CPU usage settings
CURRCPU=$(grep "<cpu_usage_limit>" global_prefs_override.xml | cut -d">" -f2 | cut -d"." -f1)
#Grab current temperature
CURRTEMP=$(sensors | grep "Core1 Temp" | head -1 | cut -d"+" -f2 | cut -d"." -f1)
#In-/Decrease usage by two percent
if [ "$CURRTEMP" -gt "$TARGTEMP" ]; then
ADVCPU=$(( $CURRCPU-2 )); else
ADVCPU=$(( $CURRCPU+2 )); fi

#Calculates pause for output on screen and also to log:
REMAINDER=$(( $(date +"%-M") % $OUTPUTPAUSE ))
if [ "$REMAINDER" = 0 ]; then
echo $(date +"%F %H:%M") Advised CPU is "$ADVCPU" %.\ | tee -a boinctemp.log
fi

#Stream EDit line with cpu_usage_limit by substituting CURRCPU with ADVCPU
sed '/cpu_usage_limit/ s/'$CURRCPU'/'$ADVCPU'/' <global_prefs_override.xml >tmp/global_prefs_override.xml
#Check temporary backup and copy to original (errors go to output AND into boinctemp.log)
if grep "<cpu_usage_limit>"$ADVCPU"" tmp/global_prefs_override.xml 2>&1>/dev/null | tee -a boinctemp.log; then
	cp tmp/global_prefs_override.xml global_prefs_override.xml
	else echo "Can't edit preferences file. Check your disk."
fi
boinccmd --read_global_prefs_override
#fi
sleep "$CHANGEPAUSE"m
done

sh ./boinc_...-pc-linux-gnu.sh

/etc/boinc-client/cc_config.xml (<data_dir></data_dir> in options)
/etc/default/boinc-client (BOINC_DIR="")
/etc/init.d/boinc-client (BOINC_DIR=)

did nothing but a broken connection with boinc-manager. Reinstalling BOINC it still saved the data in /var/lib/boinc-client ...

To whynot's guide:
If I'd known that a simple 'cp -a' is mightier than a 'rsync -whtsname' I would have saved me some time ...
Since there is already a '--bind' I thought it wouldn't hurt to mount the directory in another directory.

mount --bind /media/Harddisk/boinc-client /var/lib/boinc-client

There is a way. Set the "switch between applications" value to something that's higher than the nominal run-time of any task. In seconds, of course.

No, there isn't, sorry.

It is - over the long term.

Okay, 28000/15000 isn't quite 50/50 ;-)

Tough luck :-) they only have work very sporadically.

Depending on your BOINC version, there might be bugs that make it difficult to keep the resource share you've set, especially if you are using a GPU for crunching.