How to measure disk performance?

I always use HDTune. Simple, 'fast' and you can compare test results on their website.

IOMeter is great for measuring disk performance, there are several sites available that carry reference tables (I used one for VMWare based PC's, so I suggest you google for alternatives :-) )

EDIT: Found a very nice table on Tom's Hardware, I'm guessing the "workstation" profile seems to fit quite well...

PCWizard 2009 will do the job, it has comparison data built in. It can measure performance on other components as well.

From the site: "PC WIZARD is also a utility designed to analyze and benchmark your computer system. It can analyze and benchmark many kinds of hardware, such as CPU performance, Cache performance, RAM performance, Hard Disk performance, CD/DVD-ROM performance, Removable/FLASH Media performance, Video performance, MP3 compression performance."

SpinRite has a built-in function for measurement of read and write speed. Sequential and random.

As it boots off a CD you are sure nothing else will access the disk while the measurement is in progress.

It is hardly justified to spend USD 89 to measure disk performance, but the disk maintenance/recovery features in SpinRite may be exactly what is needed for your friend's computer.

You should expect on the order of 80 MB/s read rate for a modern SATA hard disk (e.g. WD Caviar Green). This is what I measured with SpinRite on a new Caviar Green. I once had a hard disk that was about to die and its read speed was down at 5 MB/s.