Curious iPod Question

[Ashley]

I've recently acquired a 20 gig iPod, but I was curious...now I know I'm not the math genius here, but it says I only have 18.5 G capacity. Where'd the other 2.5 go?

[Mithrandir]

One of two things:
1. That's 1024x1024x1024 to get one GB, so if you multiply 18.5 x that, you get 19864223744.
2. More likely, that's the part of the disk that's responsible for the file system. You can actually mount that file system, and do disk read/writes with it like normal. In fact, I've heard (but not done it) that you can even boot a machine from it - if the machine is capable of booting from Firewire, for example a Mac.

[Omega Amen]

I've recently acquired a 20 gig iPod, but I was curious...now I know I'm not the math genius here, but it says I only have 18.5 G capacity. Where'd the other 2.5 go?

First, let us correct your math error in your question. You should have asked, "Where'd the other 1.5 go?"

Now, to the issue at hand. Ashley, oldphilosopher quickly described the issue, but I am going to elaborate on what he is talking about so that others can learn.

For the "first thing" in oldphilosopher's list, there is a perceived loss of accuracy in describing computer memory space, which is a base 2 number, with notation that is in base 10. This approximation in notating memory space is common in all computing systems, not just the iPod. For example, look at the attached image which shows the capacity of my hard drive. Notice the difference between the "bytes" number and the "GB" number.

In reality, the "G" in "GB" describing hard drive capacity/memory space is actually 2 to the 30th power (which equals 1,073,741,824). It is not 10 to the 9th power (i.e. 1,000,000,000), which is what it normally means when not referring to computer memory.

So, if we replace the "G" with 2^30 and multiply it with 18.5:

18.5 * 2^30 = 19,864,223,744

We get what oldphilosopher got.

To see what 20 GB should yield, we do the same operation only with 20 instead of 18.5:

20 * 2^30 = 21,474,836,480

And there is a discrepancy.

This is the "second thing" in oldphilosopher's list. That discrepancy is most likely space taken up by the filesystem and the operating system, which are necessary to place data onto the physical hard disk and keep track of its contents.

So, in other words, Apple was right. Ashley, you did get a 20 GB hard drive.... It is just that some of the disk capacity has necessary software for your iPod to operate properly.

For those interested in computer memory notation, here is what some other common letters mean:

"K" is 2 to the 10th power = 2^10 = 1024

"M" is 2 to the 20th power = 2^20 = 1,048,576

and so on....

[Ashley]

Math is retarded. That's all I'm gonna say on that subject.

Thanks OldPhil for clearing that up for me (and Agasfas too for trying to tell me the same thing)

[LorentzForce]

(and Agasfas too for trying to tell me the same thing)

Agasfas? Wonder where he is in the thread...

[Mithrandir]

I *liked* omega amen's response, personally...

I'm glad to see he's got my numbers, too. I hate it when I can't do multiplication like that in my head.

[agasfas]

Agasfas? Wonder where he is in the thread...

I'm a ninja, lurking in the dark striking when you least expect. But serious, I find it quite odd why they decided to make:
1024 bytes = 1kb
1024 kb = 1 mb and
1024 mb= 1 gb

Because before being taught it in computer class a few years ago I never knew. It's like, "why not make it an even 1000mb for the 1gb? Funny how these things happen . I believe there was a reason behind confusion, but I can't exactly remember. *shrugs*

[shooraijin]

1024 is a power of 2, and computers are binary. Very simple.

Actually, it's 1024 *bytes* = 1KB, 1024KB = 1MB, and (correct) 1024MB = 1GB, so there are 1,048,576 bytes in one megabyte, and I'll leave the subsequent computation as an exercise to the really, really bored reader.

[ShiroiHikari]

I'm surprised that all this made sense to me. the math section of my brain has always been kinda...shriveled up in a dark corner somewhere. it probably drank too many sodas early on in my life, then crashed from the sugar/caffeine high and never really woke up again.

this is kinda like my old comp with the 40gb hard drive...I actually only had about 35gb because the OS/filesystem/recovery stuff took up about 5gb.

[Ashley]

I'm surprised that all this made sense to me. the math section of my brain has always been kinda...shriveled up in a dark corner somewhere. It probably drank too many sodas early on in my life, then crashed from the sugar/caffeine high and never really woke up again.

Bwahaha, I think that's what happened to mine too!

[TheMelodyMaker]

I'd say that Shoo explained it best, though I'll expand on it a little. 1024, which is 2 to the 10th power (2^10), is the closest whole-number power of 2 that one can get to 1000 -- that's probably why it was chosen as the standard for measuring RAM/disk space/etc. (I hope that was somewhat understandable. ^_^; )

[agasfas]

2 to the 10th power (2^10), is the closest whole-number power of 2 that one can get to 1000

I dont know why, but that actually makes a lot of sense.... I think I'm going to research it and find the exact answer. Curiosity has gotten the best of me....

[Mr. SmartyPants]

isn't there an actual program on the ipod that enables you to play the music? I mean, if you format the harddrive in an ipod, it'll only become a plain ol external harddrive

but that same reason applies to ALL storage stuff, loosing a few megs/gigs i mean