Hi, I am thinking about buying a laptop.  The harddrive in the laptop
spins at about 4 to 5 thousand rpm.  I could upgrade to a 7,200rpm
model at Dell, but at BestBuys they do not offer this upgrade. 
BestBuy does have a better price on the laptop I'm interested in.

So the question is:  Let's say I were to puchase the BestBuy laptop
and an EXTERNAL harddrive that spins at 7,200 rpm that is connect by
the USB cable to the laptop -- how fast is this connection compared to
a 7,200 rpm INTERNAL harddrive?

Thank you.

Hi just4fun2-ga,

    I do understand that you are interested in a higher disk access speeds
from your laptop. Most of the internal harddrives in the laptop are of
lesser rpm due to the following:
i)reduce vibrations(and increase reliability in a mobile environment)
ii)reduce the amount of heat generated/conserve battery power.
iii)actually the laptop drives are smaller(2.5") and have greater aerial
density,lighter and smaller heads(leads to faster seek times), which 
partially compensates for the performance loss.

When comparing the performance difference, you should also take note of
the builtin buffer(cache) between the two drives. A higher rpm drive of
the same size and same/more capacity and internal cache, will surely give
a better throughput, even if it is externally connected at the cost of
the following:
i)increased cpu load
ii)increased latency at the start of the data transfer
So, if you are going to use the external drive only for backup/data transfer
you idea should work fine. But booting your operating system/running
applications from the external drive may not get you much improvement
in
performance.  If you do plan on running cpu intensive applications with
your external drive(eg NLE video editing), I would suggest you to go with
firewire through a cardbus interface instead of the usb2.0, due to reduced
cpu load/latency. Also if you are going to use your external drive in a
continuosly connected manner, I would advise you to get an external enclosure
with good fan ventilation/heatsinks, since most of the external enclosures
have poor heat dissipation.

Hope you find the suggestions helpful in making your decision.

Regards
ldavinci-ga

Hi just4fun2-ga,

I forgot to mention about the UDMA interface. The external interface limits
your data transfer to about 400Mbps(50MBps/sec).  Whereas the internal ATA-100
could do 100MBps(theoretical) burst mode data transfers. You will not get the
same performance if you use it externally through the USB2.0/firewire interface.
Sustained data rate will be still better with an external drive.

Regards
ldavinci-ga

One of the greatest things about labtops are handy and portable, but
an external drive would make it less fun to carry around.  I would go
for the good deal with the internal drive.

Hard drive speed does not matter that much.  Interestingly, a well
running computer rarely uses the hard drive.  More importantly, you
should get at least 512MB of memory, or 1024MB if you want to run lots
of programs at the same time.

But to answer your question, USB theoretically could be faster, but
its not because the internal hard drive gets to use DMA, which is
Direct Memory Access.  For hard drives, I am more worried about how
noisy they are than how fast they are : ).

You can look at the speeds of the various busses here:
http://www.usb.org/faq/ans2#q1
(bits/sec)/8 = (bytes/sec)

Personally, I doubt that the faster HD would be noticably faster. 
Just save your money and get something decent.

Consider an old computer that you have.  Let's say it's a 1GHz.  When
you bought it, there were 1.3 and 1.5s around.  Would it make any
difference now if you had a 1Ghz vs a 1.5Ghz?  Would having a 1.5Ghz
give you less of a reason to get a new computer?

Also, if it's possible...try the different hard drives...Dell
Kiosk...Fry's...see if you can even tell the diff.

Actually .. you couldn't do it .. or it would be difficult I think ..
the easy way, the laptop would still have it's operating system on the
internal drive .. you could store data remotely .. but it's a lot of
hassle to carry around all the extra gear unless you have a lot of
data!   Also it would drain the battery down a lot too .. seems like
it would take away most of the portable part .. at least the easily
portable.  If the operating system were on the external drive, you
couldn't use it unless the external drive was plugged in .. ie .. as a
'laptop', unless someone was sitting next to ya'!  (;