Dell laptop running very slow due to continual HDD accesses

Hi trh01.
When you did the CHKDSK, did you run the "/f' modifier to attempt to fix the bad sectors?
Vic

Sounds like the drive you're using may have reverted to PIO mode transfers.

Go to Device Manager; expanding your IDE/ATAPI controller line; and, for each IDE channel (Primary & Secondary) do a right-click, Properties, and look on the Advanced tab to see what the "Transfer Mode" is set to (should ALL be "DMA if available"), and what the "Current Transfer Mode" is (you can't change that in Device Manager -- but the following will resolve it).

If ANYTHING shows a "Current Transfer Mode" of PIO, then do the following (actually, it won't hurt to just do this anyway -- this is a harmless mod that just forces redetection of all of your IDE devices transfer modes):

Load RegEdit (Start - Run - Regedit)

Go to the following keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\ Class\{4D36E96A-E325-11CE-BFC1-08002BE10318}\000x

The last four digits will be 0000, 0001, 0002, 0003, and so on.

Under each key, delete all occurences of the following values:

     MasterIdDataChecksum
     SlaveIdDataChecksum

Now reboot your system and see if the problem disappears.

I think you should run a memory test. Erratic RAM can cause logical HD errors and weird behaviour in general.
/RID

Thanks for all the idea guys.  I have now managed to find one of those 3.5" to 2.5" converter cables and hook up both drives to a desktop machine.   The results were as follows:

HDD 1:   still readable by the OS, but Sandra shows that the read performance drops from around 15Mbits/sec to 10s kbits/sec for certain sectors - thus indicating that the disk is on its way out, and if we presume that critical OS files are in this area, then it explains the very slow behaviour.

HDD2:  is similar to HDD1, except that affected sectors are in different places.

So the answer is that both HDDs are faulty - not what I wanted to hear, but exactly what Zoplax suggested.

En route I did check the other ideas.   The RAM was tested by Dell Diagnostics and was fine - though I agree with rid that it was a possibility.

CHKDSK was run with the /r modifier, which I suspect behaves similarly to /f.   I didn't use /f because it wasn't offered in the menu of modifiers, when I ran CHKDSK.  I wonder if this option has been removed in the WinXP version of CHKDSK?  (I had booted from a WinXP CDROM, so it presumably came on this CD)

The suggestion from garycase about DMA settings was also checked.  It turned out that the disks were running in UDMA mode 2.

Whoa !!  "... the read performance drops ... for certain sectors ..." ==>  This is NORMAL.  All modern drives use zoned sectoring;  so the performance on outer cylinders is much better than on inner cylinders.   The drives MAY be bad (especially the first one), but don't base that conclusion on the variable read performance.   The problem could very well be a faulty IDE controller.   Run a good drive diagnostic on the new drive while it's connected to the desktop.

Yes, of course the performance drops depending on the sector.  In fact Sandra produces a rather nice graph showing read speed against position.   And for most of the drive the speed varies between about 12 and 18Mbits/sec.  As you say it drops off on the inner cylinders.  

 But when it drops down to near zero for certain positions I think its reasonable to assume that that is the cause of the slowness I have been seeing.   Speed on these positions was around 2 - 3% of the rest of the disk.