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How to replace the Hard Drive in an iMac G3 333Mhz (Tray Loading) computer

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Need More Disk Space!

I recently installed Virtual PC on my trusty iMac G3 333Mhz Tray Loading computer hoping to run a copy of Windows XP for testing purposes.

During the install of Windows XP I noticed that I didn't have enough disk space on the internal disk drive of the iMac to house the Virtual Hard Drive (VHD) file needed for the install.

So I had to make a choice...


Sure, I could have installed an external USB hard drive to house the large Virtual Hard Drive (VHD) file needed for the install of Windows XP, but I didn't like the look of an external USB hard drive hanging off the side of my iMac. I chose a more streamlined approach of replacing the puny 6GB hard drive in my iMac with a much larger 40GB hard drive.


What type of hard drive do I need?

I will be the first to admit that I am not a "Mac Guru". I have worked on PCs for most of my career in the Information Technology field so I was not sure if I needed a special hard drive manufactured specifically for Mac computers. Through my research I determined that any IDE/ATA Hard Drive designed for a PC will work in my iMac G3. In fact ATA66, ATA100 and ATA133 hard drives will all work great. These hard drives come in 2 speeds, 5400rpm and 7200rpm. Both will work but a 7200rpm will give your iMac a little speed boost. Please note, the maximum capacity hard drive for an early model iMac is 120GB, so don't go wasting your money on a hard drive greater than this capacity.

It is pretty easy to install a new hard drive in an iMac G3 computer

You can get to the logic board/drive assembly with the removal of a couple screws.

Safety First!

Please make sure your iMac G3 is unplugged before disassembling it.


Disassembly work space

You need plenty of room for the disassembly process; I used a 24 inch by 48 inch folding table that I knew could hold the weight of the G3 iMac. So as not to scratch the case of the iMac, I recommend putting down a soft towel on the table, I used a car chamois.

Disassembly - Step 1


Actually I didn’t think to take any pictures until my iMac was already disassembled so I am going to show you the pictures in reverse.

Turn the iMac upside down on the soft towel that is covering the table. The first thing that needs to be done is to remove the bottom cover. The cover starts at the blue Apple logo and ends where the two feet are located just past the last vent. See area circled in the picture.

Disassembly - Step 2


Remove the screw between the handle/stand toward the back of the iMac. Pull the bottom cover away from the computer. This will expose the logic board/drive assembly. See area circled in the picture.

Disassembly - Step 3

Disconnect the three cables at the bottom of the logic board/drive assembly; see areas circled in the picture.

Disassembly - Step 4


Remove the two screws inside the handle that hold the logic board/drive assembly in place. See areas circled in the picture.

Disassembly - Step 5

Scroll to Continue

With one hand on the plastic handle, gently pull the logic board/drive assembly straight back being careful not to pinch any wires.

Here is the picture of the logic board/drive assembly removed from the iMac.

Disassembly – Step 6


Time to remove the CD-ROM, It is quite easy to do but you want to pay close attention to what you are doing because it will make it much easier when you go to reassemble it. The CD - ROM is held in place by a spring. What you need to do is to is raise up the front of the chassis and with your thumbs push back on the front of the CD-ROM until the two small tabs have cleared their slots, then push up on the CD-ROM and it should raise up. Push on the areas circled in red in the picture.

Disassembly – Step 7

Remove the IDE cable from the back of the CD-ROM drive, and place the CD-ROM to the side. See area circled in the picture.

Disassembly - Step 8


With the CD-ROM out of the way you will be looking at the top of the hard drive with the spring on top of it. Remove the spring from its slots and place it to one side. Gently lift up the logic board/drive assembly and look at the bottom side. Notice the two small tabs they hold the back end of the hard drive in place. Do not tamper with these tabs, just take note of their position, you will need to look at them in the next step.

Disassembly - Step 9

Locate the two screws, one on either side of the of the chassis frame, these hold the hard drive bracket to the chassis. Remove those two screws then remove the carrier from the case by sliding it up. See area circled in the picture.

Disassembly – Step 10

Remove the IDE and Power cables from the back of the hard drive. See area circled in the picture.

Disassembly - Step 11


Remove the screws that hold the hard drive in the tray, there are two on each side of the hard drive. See areas circled in the picture.

Disassembly – Step 12


Here is a picture of the puny 6GB drive removed from the tray.



Reassembling the iMac G3 is the opposite of the disassembly process start with disassembly step 11 and countdown to disassembly step 1. Please note: It is very important that you set the jumper setting to Master on the replacement hard drive before installing it in the tray, failure to do this will make the drive undetectable to the iMac! On my Seagate Barracuda drive you move the jumper to the pins closest to the IDE connector, this setting varies with manufacturers and model of hard drives. On the drive itself there is usually a sticker that explains jumper settings.

First Boot after hard drive install


When you boot up for the first time after the hard drive install you should hear the familiar chime indicating that the hardware is fine then you will see a folder icon with a question mark on the screen. This indicates that your iMac can't find the operating system. This is normal as we have not yet installed an Operating System on the new hard drive yet.

Installing the Operating System on the newly installed hard drive

Here are the steps to install an Operating System on the newly installed hard drive:

1. Boot the iMac, you will get the folder icon with a question mark on the screen as discussed in the previous step.

2. Insert the Mac OS X CDROM Disc 1 in the CDROM drive. The iMac should immediately boot from CDROM and the folder with the question mark on it should disappear.

3. Select English for the main language then click the Continue button.

4. Click the Continue button in the "Welcome to Mac Installer" window.

5. Choose Install from the menu then Disk Utility from the drop-down menu.

6. In the left hand pane choose your newly installed hard drive, it will most likely be named after the model and capacity of your hard drive.

7. Click on the Erase tab, then select Mac OS Extended (Journaled), a name for the hard drive , make sure "Mac OS 9 Drivers Installed" is selected then click on the Erase button.

8. Click on the Partition tab, select 2 Partitions from the volume Scheme Drop down box. This will give you two equally large partitions adding up to the sum of the total hard drive capacity. Now this is very important, the partition on which you install the Mac OS X on must be less than 8GB. Carefully move the separator bar between the partitions until the top partition is 7.49GB in size. Select each partition and give them an appropriate name.

9. Close the Disk Utility.

10. Click the Continue button in the "Important Information" window.

11. Click the Continue button then the Agree button in the license agreement window.

12. Select the destination hard drive, it must be the drive that is less than 8GB, then click on the Continue button.

13. Click the Install button.

14. Insert Mac OS X CDROM Disc 2 when prompted.

15. Select No to transfer information then click the Continue button.

16. Choose United States then click the Continue button.

17. Enter your Apple ID or create a new Apple ID then click the Continue button.

18. Enter registration information then click the Continue button.

19. Select "Use Existing Internet Service" then click the Continue button.

20. Select "Local Network (Ethernet)" then click the Continue button.

21. Choose Yes to "Configuration supplied by the server" then click the Continue button.

22. Select "Sign Up for .Mac membership later" then click the Continue button.

23. Click on the Continue button in the network setup window; choose "Register Later" if prompted.

24. Enter e-mail information in the e-mail setup window, or just click on the Continue button.

25. Select the proper time zone then click on the Continue button.

26. Set the proper date and time then click on the Save button.

27. Click on the Done button, operating system install complete!


With a little determination and some free time, you too can install a new hard drive in your iMac G3.

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jbdkz (author) from Cleveland on March 17, 2014:

@tysam lm: Sorry to hear, the G3 was a great little was the first Mac I ever owned.

tysam lm on March 17, 2014:

Wish I would have seen this lens before! Recently sold my working G3 iMac because I didn't have enough room to put all my stuff on it and have the Os that I wanted ...

jbdkz (author) from Cleveland on January 17, 2014:

@PaigSr: The Lens makes it look easy but it did take me three evenings to complete the task. Hopefully this lens will help others.

PaigSr from State of Confusion on January 17, 2014:

Not to sound annoying but - been there done that. And I really wish I had your information back then as it would have made the whole thing a lot easier.

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