KB-40011 Flash-modding iPod Classics - Compatible capacities

Flash Modding iPod Classic

iPod classic and iPod video can have their hard drives replaced with flash storage. But depending on the exact model, there are limitations.


RAM vs Storage

The files on the iPod are stored in the main storage, but a database of your files are loaded into RAM. Depending on the original capacity of the iPod, it will have either 32MB or 64MB or RAM. A1136 30GB models have 32MB of RAM installed, while other A1136 models have 64MB. A1289 160GB have 64MB of RAM, while other A1289 models have 32MB.

It is generally seen that 64MB of RAM can handle music libraries up to about 50,000 individual items (ie tracks, videos). There is no limit hard-coded in the iPod system, so iTunes or the iPod will not prevent more tracks being synced. However, if the track database fills the iPod RAM, then there is not enough RAM to run the system software. In this instance, the system crashes and the iPod may either reboot endlessly or freeze completely and not respond to input. In either case, you should reboot and enter disk mode to restore the iPod.

The RAM limit can be probed using the shuffle all feature in some iPod classics. When large libraries are synced, the shuffle all feature will become sluggish to begin, as the RAM of the iPod becomes closer to completely full. Eventually, as the size of the library grows, the shuffle all feature will crash the iPod. At this point, syncing even more tracks will likely crash the iPod on startup.

There is a track limit independent of capacity in iPods. If your library is more than 40,000 tracks, you might find your iPod behaving differently. If you have over 50,000 tracks, your iPod will likely not work at all

These RAM-based track limits were not commonly experienced when using the original hard drives. With the largest 160GB hard drive, the storage would be full after around 30,000 tracks, even if those tracks were low quality, small mp3 files. Therefore, there was no need to install larger RAM modules or store the database in a different way. Only after very large flash storage devices became available and capacities of 512GB, 1TB, or higher were accessible did the RAM limitation become apparent to more users.

A possible way to avoid this is to use Rockbox as an alternative System Software.

Storage vs logical addressing

The second important consideration when flash-modding an iPod classic is the type of logical addressing used by the system. Logical addressing is a characteristic of the main board of the iPod and cannot be changed. For the purpose of this article, there are two types of addressing: LBA28, and LBA48.

Almost all iPod classics use LBA48 addressing. LBA48 has a maximum addressable storage of over 100,000 TB, so there is no reasonable method of reaching the LBA48 limit.

LBA28 is different - it has a maximum storage of 128GB*. The only iPod that utilised LBA28 addressing is the original A1289 iPod classic, commonly known as the 6th and 6.5 generation. Specifically, this includes any 80GB or 120GB iPod classic, and also the original 160GB version. The late 2009 iPod classic 160GB uses LBA48.

*This limit is calculated by multiplying four values: the number of 'cylinders' 'heads', and 'sectors', and the sector size. cylinders, heads and sectors are characteristics of the storage system, and have maximum values. The sector size is almost always 512 bytes. However, the 160GB hard drive in the original A1289 uses a large byte sector, allowing the full 160GB to be readable, and not limited to 128GB. However, sector size is not alterable, so modern drives (including all SD cards) use 512 byte sectors, meaning the limit is 128GB.

Therefore, if you are interested in flash-modding your iPod, you should be mindful of two things - the RAM of the model you have, and the logical addressing. Logical addressing is a hard limit and can't be bypassed. RAM is trickier to find a definite limit for, but can be tested for and worked around if needed. See the table below for a basic guide:



Partition size limit

Finally, iPods must be formatted for use using one of two file systems: 'Macintosh' (ie HFS+) or 'Windows' (ie FAT32). FAT32 has a maximum partition size of 2TB (using the parameters that the iPod classic supports). While HFS+ has a much larger limit, iPod classics are limited to 2TB for either format.


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