I have a desktop hard drive (1 TB) I removed from my computer and want to use it as an external drive. Looking online, I see there are a number of ways to do that.
However, I'm not very familiar with the inner workings of computers or computer terminology, and don't understand the implications of the various terms mentioned. I also don't know what I don't know, so seeking clarification on what might, for my case, turn out to be irrelevant factors may leave out something important it is assumed I would know.
What do I need to know to identify the correct hardware to connect my hard drive as an external drive; i.e., what are the critical factors for selecting compatible hardware that will enable me to connect the drive via USB?
33 Answers
What do I need to know?
Interface devices
There are basically three ways to connect a bare hard drive externally: docking station, as suggested by @sawdust; an adapter cable, as described by @ivanivan; or an enclosure, also mentioned by @sawdust and @ivanivan. The interface electronics is the same in all three, the difference is in the physical housing.
The adapter cable route leaves the bare drive exposed, and is generally used for a temporary connection. You can get adapters that handle just IDE or just SATA, or a kit like this that connects virtually any common hard drive (never used this particular example, it's just for illustration):
Once you own the adapter (and they're inexpensive), you can reuse it with multiple drives on a temporary basis as needed. They aren't ideal for anything approaching a permanent setup. There is nothing securing the connection, there may be multiple cables taking up workspace, and the bare drive has nothing protecting it from spills or accidentally shorting the exposed electronics.
A docking station provides a little stability and protection. One like this will hold either a 2.5" or 3.5" SATA drive (again, no personal experience with it, just for illustration):
The main use for a docking station is if you have a number of drives that you want to use interchangeably. It is easy to plug and unplug drives as needed, and offers some protection for the drive and the connection while the drive is docked.
An enclosure protects the drive and turns it into what you see sold as an external drive. The case is a little larger than the bare drive, and houses both the drive and the interface. Enclosures are designed for a single form factor and type of drive interface, so you buy one to match your drive. You can reuse an enclosure with another drive, but they aren't intended as a mechanism for actively swapping drives on the fly.
Regardless of the style of the interface device, there are five things you need to consider:
Drive form factor
If you use a docking station or enclosure, it needs to be for the drive's form factor (3.5" vs. 2.5"). An enclosure for a 2.5" drive may also need to consider its thickness. Some enclosures are "slimline" and may not hold thicker drives that are common with larger capacities and multiple internal platters.
The 2.5" and 3.5" designations refer to the diameter of the platter inside. The actual size of a 2.5" drive is roughly 2.75" x 4". A 3.5" drive is roughly 4" x 5.75". In both cases, thickness can vary. Use those measurements to identify the form factor of your drive.
If the drive has an IDE interface, 2.5" drives have a smaller connector than 3.5" drives. If you go the adapter cable route, those commonly have a double-headed drive connector to match either form factor. One other difference is the power connector. A 3.5" IDE drive has a separate, large power connector. On a 2.5" IDE drive, there is not a separate power connector. Instead, the IDE connector has a few more pins for the power.
Drive interface
The drive connection needs to match the drive interface. The connection inside your computer will look similar to one of these (3.5" drives shown; upper image is IDE, lower is SATA):
Courtesy Hetman Software
If it is an old drive, it may have an IDE (also known as PATA) interface. On a 3.5" drive, this is a connector with 40 pins arranged in two rows of 20 pins. The connection inside the computer is a wide ribbon cable (on an external adapter, it's likely to be a round cable). The connector has a molded key so it will only go in one way. On a 2.5" drive, the IDE connector is similar but smaller, with 44 pins instead of 40.
Note that there may be an additional small block of pins next to the IDE connector, possibly with a jumper inserted. You normally do not need to do anything with these pins or change the jumper. If you have a question related to these, like you accidentally knocked off a jumper and don't remember where it was, that would be the subject for a separate question.
A newer drive probably has a SATA interface. Instead of rows of pins, the drive has two "blades" in a single row with embedded contacts. One blade has the data connections, the other has the power connections.
Power
A 2.5" drive is likely to get sufficient power from a USB connection, particularly if it is USB 3.0. They require only 5 volts, which USB provides, and a single-platter drive is likely to have power requirements even within USB 2.0 capacity.
A multi-platter (high capacity) drive is still normally within the USB 3.0 power limit, but may exceed what USB 2.0 can provide. In that case, the power can be supplied from an external source (a wall power adapter). Some enclosures come with a USB "Y" cable to tap additional power from a second USB 2.0 port. For a drive of smallish capacity, you might not need to sacrifice a second port to plug in the extra leg of the cable even if an external power source can't be used.
A 3.5" drive will require an external power source. They require 12 volts in addition to the 5 volts, and that isn't available from a USB connection. Their total power requirement is also more than a USB port can provide, so the higher voltage can't be created from the USB connection. Whatever connection device you choose, that is designed to handle a 3.5" drive, should come with a wall adapter for power.
Note that there are adapter cables sold that are designed to work only with 2.5" SATA drives (they have no external power provision). They will fit a 3.5" drive because both use the same connector. However, you can't operate a 3.5" drive from them.
USB Interface
Most external connections use a USB interface. A slow hard drive has a peak data transfer rate a little faster than a USB 2.0 interface. A fast hard drive can have a peak rate several times USB 2.0 capacity. USB 3.0 has bandwidth much higher than the fastest hard drive, so there will never be a bottleneck.
If you have a USB 3.0 port and use a USB 3.0 connection, the drive will have essentially the same performance as it did internally. A USB 2.0 connection will provide degraded (i.e., slower), performance compared to its internal use. How noticeable that will be will depend on how fast the drive is and what you're doing with it.
Booting
If you intend to boot from the external drive, or want the option, and leave or recreate a boot provision on it, the computer will need to look there. You can manually select the boot device at start up (there is usually a brief prompt when it first starts telling you what key to press), or you can set the computer to always give first priority to a USB-connected drive if one is there.
If you will only connect the external drive when you want to boot from it, setting USB as the first drive to check will still boot from the internal drive if the external drive is not connected. If the external drive contains Linux and GRUB, you can leave it connected and GRUB will let you select the internal drive. You can even make the internal drive the default, so it will load from there if you don't pick something else.
6There are various manufacturers that have kits for one-off connections. The one I have has a power brick wtih both molex and sata power heads and a USB dongle that has sata, IDE, and laptop style IDE interfaces on it. Between these 2 a workable combination for all non-SCSI drives is possible. Search for "USB to IDE adapter kit" on your preferred search engine. Walmart, Amazon, Aliexpress, etc
If you want something more permanent, you'll want to spend the money for a kit that comes with an enclosure of some type for the drive itself get a enclosure separately.
Image via Creative Commons search on Flickr
A double USB cable or a micro USB - USB cable can usually solve the problem. But it really depends on what type of hard drive you have. Cables like this: USB-USB or this: Micro USB - USB may be helpful. Again, it depends on what kind of hard drive you have.
1
