Changing the hard drive in a iBook is far from the normal procedure for a regular PC laptop. The hard drive is an intergrated part of the system and thus requiring a lot more work to get to.
I'm going to install a new and faster Seagate 40 GB hard drive; 5400 vs 4200 RPM, 2 MB vs 8 MB cache and the equal power usage. Approx installation time is about 1-2 hours, depending on previous experience.
Old: IBM Travelstart 20GN 10 GB (Apple branded)
New: Seagate Momentus 40 GB
The new drive can not be higher than 9.5 mm. Drives larger than 40 GB usually contains more internal disks and is then a bit higher.
Apple iBook Dual USB Service Manual
While disassembling it's a good pratice to group the parts into separate sections, i.e. screws for the bottom case, the feets and the case itself into one group.
| Remove the three screws in the centre and top using a T8 torx screwdriver. | These are a bit longer. | Screws removed. | 
| Remove the battery springs, try not to waste the grease. | Four more screws to remove. | The screws inside the battery compartment. | 
| Screw holding the sleep light. | Right-most screw holding the top case. | Force the optical drive to eject using a small screwdriver or paperclip. | 
| Turn the iBook around and remove the small magnet used to hold the keyboard in position. | Then remove the screw under the magnet in addition to three others. | Screw removed. | 
| Tear up the tape hiding the speaker cables. Don't throw this away, you need it later when re-assembling. | Carefully pull the trackpad ribbon cable out of the connector. | Losen the speaker cable. | 
| Now disconnect the power button cable. | Power button cable disconnected. | 
| Remove the 12 screws, yes twelve, to remove the top metal shield. | Screw removed. | Screws removed. | 
| Screws removed. | Screws removed. | Screws removed. | 
| Peal the three yellow tapes away but not entirely just enough to free the metal shield. | Lift the tape covering the modem and ethernet ports. | Peal away the tape next to the trackpad connector. | 
| Lift the metal shield and push from beneath to relase it in the upper-left corner, without bending it too much. | 
| Side by side; Seagate left, IBM right. | Seagate ST94811A | IBM DJSA-210 | 
| Side by side; Seagate left, IBM right. | Seagate ST94811A | IBM DJSA-210 | 
| Interface on the IBM drive. | Interface on the Seagate drive. | I noticed that there are two possible ventilation holes on either side of the interface. Unconfirmed though. | 
| Rigt side. | Reattach the microphone cable and tape it down. | Installed successfully. | 
When you re-assemble the iBook and happen to forget where some of the screw locations are, there is a great section in the service manual showing all the screw locations.
Audiable wise the drive is a tiddy bit less noisier than the old IBM drive when operating, but it still accentually resets creating a noticable disk read/write noise.
Since the hard drive is sitting directly above the system controller I didn't notice any heat increase or decrease. The system controller is generating a lot of heat and it's poorly ventilated with only a heat transfer patch between the bottom shield and the chip.
Anyway, it's certainly generating so much heat that it get's uncomfortable after a while when it's sitting on my lap.
I used IOzone to benchmark the drives. IOzone is a filesystem benchmark application creating a detailed throughput report. The output data can be used to create advanced graphs for easier analysis. IOzone has been ported to multiple operation systems and architectures, check the references.
I ran the suggested command-line from the OS X port page.
| ./iozone -i 0 -i 1 -Rab output.wks | 
The benchmark process is time consuming, so it's best to find something else to do for 15-30 minutes in the mean while. My iBook has a total of 384 MB of RAM installed and it will make a distinct impression on the benchmark when it hits that mark.
Installing HD Replacement [pbfixit.com]
			iBook 500 HD Replacement [utexas.edu] [pdf]
			IOzone for Mac OS X [hut.fi]
			Iozone Filesystem Benchmark [iozone.org]