Stilly -

Older computers used hard drives with IDE or EIDE controllers. For either of these, the controller can handle a maximum of four drives. The drives connected to the controller often include a floppy drive, ZIP drive, and/or "optical" drives (CD and/or DVD readers or burners). You cannot install more than one EIDE controller in most machines. Often, without removing an existing drive, you can't install more than one, or at most two hard drives directly in the computer.

The simplest workaround that I've found, if you have EIDE hard drives, is to install a hard drive in a "USB box." The box has an EIDE interface inside, facing the hard drive, and a USB interface outside, facing the computer. A separate USB/EIDE interface, and hence a separate box, is generally required for each hard drive, but you can (theoretically) connect up to 8 USB "devices" to a single USB port.

If you have the newer SATA hard drives, it's possible to connect more than four SATA devices, but I can't offer details since I've only seen one computer with SATA hard drives in it, and haven't needed to multiplicate them.

Most of the external USB hard drive boxes previously available can only be used with EIDE hard drives and a different kind of box is needed for use only with SATA hard drives. Of course either kind can be put in an appropriate USB box, and boxes are available for either kind. You have to pick the box to match the kind of hard drive you intend to put in it.

There are a few boxes available that can take either kind of hard drive, using one set of internal connectors for EIDE or a separate set of connectors for SATA drives. leaving the unused set just hanging (actually "stuffed" is a better description) inside the box.

When you connect a USB device to your computer, it will appear with a "drive letter" to identify it.

If you have a network connection to another computer, you can also "Map Network Drive" to any shared drive, or a to any shared folder, on the other computer so that it will appear to be a drive, with individual drive letter, on your own computer. (Windows Explorer, Tools, Map Network Drive.) WinXP and Vista will not willingly let you share the root on the System drive of a computer, and it's not recommended but can be done. A drive that doesn't contain the Windows system stuff can be shared "entire."

About the only problem I've found with Hard Drives in USB boxes is that the boxes "hold the heat" and stacking boxes on top of each other can cause a lot of heat buildup that may be damaging to the drives inside. (A rack with shelves and a cooling fan might be a good idea, but keeping the drive boxes on separate ventilated shelves, or side-by-side with a little space, also works.)

It should be noted that, in my experience, a desktop Hard Drive in a USB box does not make the drive portable. No matter how carefully it's handled, premature failure of a desktop HD is inevitable if it's carried around at all, inside or outside of a box.

John