Q: I have a feeling that my hard drive is on its last legs. it is old and only 150 gig. CAn I replace it and duplicate everything on it??

Your going to need to be able to make a copy of your data.

You may want to consider buying and using an external drive for your daily use.

I believe the g5's have a firewire 800 port.

In case you decide to replace your internal drive.

iMac g5 is SATA 1.0

• 2.1 SATA revision 1.0 - 1.5 Gbit/s - 150 MB/s

Check to make sure you can reduce the speed to 1.5.  Some 6.0 drives have a plugable pin to reduce to 3.0 then auto negotiate from 3 to 1.5.

You can buy a dongle for 15 to 20 dollars to temporarily attach a harddrive to your system.

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You need an external Firewire drive to boot a PowerPC Mac computer [ a few G5's will boot from USB ]. 

I recommend you do a google search on any external harddrive you are looking at.

I bought a low cost external drive enclosure. When I started having trouble with it, I did a google search and found a lot of complaints about the drive enclosure. I ended up buying a new drive enclosure. On my second go around, I decided to buy a drive enclosure with a good history of working with Macs. The chip set seems to be the key ingredient. The Oxford line of chips seems to be good. I got the Oxford 911.

I'd give OWC a call. 1-815-338-8685.

FireWire 800 + USB 3, + eSATA

&

save a little money interface:

FireWire 400 + USB 2.0

This web page lists both external harddrive types. You may need to scroll to the right to see both.

http://eshop.macsales.com/shop/firewire/1394/USB/EliteAL/eSATA_FW800_FW400_USB

     (2) FireWire 800/400 Ports (Up to 100MB/s / 50MB/s)

     (1) USB 3.0 Port (Up to 500MB/s / 60MB/s)

     (1) eSATA Port (Up to 300MB/s)

Has a combo firewire 800/400 port.  Not sure what this is.  Looks like you will  need 400 cable.

http://eshop.macsales.com/shop/ministack

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Carbon Copy Cloner will copy your startup drive to an external  firewire drive.  You can boot from the external drive to verify that you have a good clone. When you upgrade your existing startup drive, you can at any time boot from your external drive and go back to your existing system.

http://www.bombich.com/software/ccc.html

SuperDuper is the wildly acclaimed program that makes recovery painless, because it makes creating a fully bootable backup painless. Its incredibly clear, friendly interface is understandable, easy to use, and SuperDuper's built-in scheduler makes it trivial to back up automatically. And it runs beautifully on both Intel and Power PC Macs!

Give SuperDuper a workout on your own system. Clone to your heart's content — for free. See what else is possible. When you're convinced that SuperDuper is a terrific solution — and a great value at $27.95 — you can register right from the application and start using its advanced features immediately!

http://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html

To boot from the external drive, hold down the option key when you poweron your system. Pick the drive you want.