Why Does iTunes Continuously Read From the Hard-drive?

Hi. I have recently discovered an odd behaviour from iTunes: instead of reading an entire song from the harddrive and storing it in ram during playback, iTunes reads small chunks of data very frequently. For example, when playing a 128Kbps song the HD reads 68KB chunks approximately every 3 seconds, and when playing lossless WAVE files the HD is constantly reading at 200KB/s. I found this out by having iTunes open and playing music while having all other programs closed, and monitoring the disk activity from Activity Monitor (and I'm sure that it's iTunes that was reading from the HD because when the music was paused the HD was idle).

So, my question is why would iTunes do this? This seems like an extremely inefficient use of the harddrive for several reasons:
- Constantly reading small chunks from the HD uses much more power than reading large chunks infrequently because idle hard-drives use much less power than active hard-drives
- This will slow down other applications that need to make heavy use of the HD because iTunes will be constantly interrupting anything else that is using the disk (this is especially true for Photoshop or any other program that uses lots of swapfile space)
- It puts unnecessary wear on the HD heads
- It is dangerous for laptops, which can easily get thrown around or bumped. Momentarily reading a large chunk of data and leaving the HD idle for the majority of the time will be much safer for the HD heads
- Hard-drive-based portable music players read large chunks of data infrequently because it is well-known that this saves power and protects the HD in these devices.

So... is there any reason that iTunes is exempt from these reasons??

-Eric

PS: I originally posted this on the Apple Discussions, but wasn't able to get an answer there.

 

I know a thing or two about them, but I've never built one or done much programming for one, so I've never seen the code or algorithms for how they work. I'll take your word that they're efficient.

I know about the sudden motion sensor. Actually, I've seen it working many times on my MacBook. But nevertheless, parked harddrive heads are safer than SMS-protected one.

 

Ya, there's definitely a lot of circumstances where loading most of the song would be advantageous. I was going to submit feedback to Apple about this, but thought it'd be better to see what others had to say about it first. I'm guessing that Apple did at least some research to figure out which HD-reading method would be the best.