The iPod touch doesn't have a hard drive, it has flash memory. You can get it in up to 64GB.
You cannot upgrade an iPod Touch's flash drive to a larger capacity. The flash drive is what it is on an iPod Touch. You cannot change it, increase or decrease it.
The iPod Touch has an 8GB, 32GB or 64GB flash drive.
You cannot add space to an iPod Touch hard drive, or any other iPod hard drive. The hard drive capacity is set and cannot be changed.
Buying it
The iPod Touch's box should say the capacity of its hard drive.
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The iPod Touch comes with either an 8GB, 32GB or 64GB flash drive. There isn't an 18 gigabyte iPod Touch, nor is there an 18th generation iPod Touch.
be patient, the time will come where you find a cheap ipod touch, but for now, wait
This is dependent purely on how big the hard-drive inside your iPod Touch is.
No, you can't. The amount of gigabytes your iPod touch has is fixed into its hard drive, and you cannot increase it.
A refurbished iPod Touch is an iPod Touch that has been sent back to the factory, had the hard drive wiped and cleaned, and refitted with a brand new screen and outer part.