Hello freechess,
No. You need another computer. The only way to use an external drive is to use it as a replacement for your internal hard drive by reinstalling BOINC on the external drive.

Lawrence

freechess I'm afraid installing another copy of BOINC on the external hard drive will not increase your output. You need another computer as all the computation is done on the CPU. It doesn't matter where BOINC is installed. You can try running two installs of boinc, or running one in the real machine and another in a VM running on your real computer, but it will make no difference. It won't increase your output, in fact it'll probably reduce it as you'll be swapping CPU time between different BOINC installs. There will be CPU cycles used in doing the swapping.

If my guess is correct you have joined to "mine" ripples with the Ripple Labs team. You should be aware that things like the specialist plug-in ASICS Bitcoin miners use will be useless and there are no similar items for WCG due to the varying nature of the Work Units.

There is no way to shortcut the system. If there were then the old hands on WCG would already be doing it. All you can do to increase your output is either buy another computer, or overclock your current computer (may not be possible - limited overclock options on most pre-built systems from major manufacturers).

If you are running Windows, you may find a speed boost by running a Linux 64 bit Virtual machine. Linux has better return times. If you do this, I would let the VM do all of the processing. Set it to use all of your cores. You could even put it on the external, but I think you would lose performance doing that.

BOINC manager is just that, it manages the client tasks (work units) on your computer. To run more work units the choice is therefore to run more CPU cores, with one thread per core, run hyperthreaded cores, (ditto) or run more CPU crunching power.

Getting the most from WCG thus turns into a cerebral juggling act of getting the most CPU cores running at the fastest speed, for the least amount of power consumption and heat/noise output. With hyperthreading , a four-core CPU can work on eight work units at once, so rather than run multiple CPUs (as in multiple computers) it's better to think in terms of available cores.

Later multicore CPU's outperform those from even four years ago by a huge factor, so it may be that rather than run several older boxes at home, an upgrade to one or two systems running Sandy Bridge or Haswell i7's at 100% over all eight (or more) 'cores', 24/7 is a better option and will crunch higher numbers for the same amount of electricity, or less.

This then leads you into building dedicated crunch-boxes for WCG which will run eight or more cores 24/7 without melting, or driving your family out of the house with the heat and noise. Fortunately, 21st century technology now makes this easy. Almost-silent 8-core i7 boxes can run on air-cooling, 24/7.

Dual-cpu boxes offer further possibilities for massively powerful crunching, at some cost.

Of course, the above is an idealistic cost/benefits analysis which ignores capital expenditure or power costs; so if you have several existing older boxes then running them will still benefit the WCG.