The T-Mobile G2 was supposed to come with 4GB of internal storage, yet when devices (including my own) starting hitting the shelves, Android was reporting a little less than 2GB available.
Theories flew about where the “missing 2GB” was. Some claimed that many of the G2s accidentally got the storage chip intended for the HTC Desire Z (essentially the same phone, with half the internal storage).
I even jumped into the fold, hypothesizing that the “missing 2GB” had something to do with the way T-Mobile and HTC were locking the phone, to automatically revert any changes to the ROM — the “missing 2GB” would essentially have been a recovery partition, or a “shadow installation” of the OS.
A new theory has surface that, although extremely technical, seems to not only explain the missing space, but also corroborates T-Mobile’s explanation that the discrepancy was due to “creative partitioning”.
On with the technical mumbo jumbo!
Internal flash memory, like the Sandisk chip (also known as an “emmc”) stores information. The way they they do this is where the techno-babble comes in. There are two basic ways to store information in a flash memory chip: SLC (single-level cell), and MLC (multi-level cell).
When configured for SLC, a single bit of data is stored in each memory cell. When configured for MLC, you can store 2, 3, 4 or more bits of data in each cell. You essentially get a lot more capacity with more bits per cell (“density”). There’s a trade-off to doing this: you lose both read and write speed, and your reliability is reduced.
An article from Toshiba reportedly states the following:
Those areas requiring better reliability are SLC or can be programmed as SLC … the Enhanced User Data Area, which may store, for example, system log files, are SLC. The User Data Area, which may store music, pictures, videos and other files is MLC … Each 1 bit configured as SLC results in 2 bits less of MLC. Theoretically an 8GB e-MMC device (densities are defined in MLC terms), could be configured virtually all as SLC and thus would be approximately 4GB. In most cases, it is more likely that the majority of the memory would be configured as MLC to support higher density.
Did Sandisk or HTC follow the same logic that Toshiba put forth in their datasheet? If so, there’s some bad news: the Enhanced User Data Area “can be programmed only once during the device life-cycle (one-time programmable)”. In other words, if that’s the case, the “missing 2GB” is non-recoverable.
So although the capacity (“density”) is cut in half, if this is the case, the benefits are faster performance and greater stability and longevity.