Fundamental Qi question

Werner Almesberger werner at
Thu Jun 4 15:00:39 CEST 2009

arne anka wrote:
> - what reasons make you say, sd is the future?

The main reasons are:

- much easier handling. SD is like a disk, so you can use all the
  standard tools and get standard behaviour. NAND needs a lot of
  exceptional treatment to properly address wear and factory-bad
  blocks. I.e., you can't just pretend it's a regular disk but
  need special file systems, special tools, special partitioning,
  and all that.

- the price/performance point of SD is set at the time you buy the
  SD card while that of NAND is set when the device is designed.
  So NAND always lags behind trends in capacity growth.

- if all the data of a device is stored on SD, you have a lot more
  flexibility when moving data across systems. E.g., you could
  share a phone among people, use multiple phones with the same data,
  have completely separate work/personal or regular/travel
  environments, etc.

> - what reasons, except the impossibility to replace the nand when it is  
> worn out by to many write operations, led to the decision to use nand  
> read-only?

The complexity of recovering from catastrophic NAND corruption. With
GTA01, you needed the debug board. GTA02 has an expensive and (for
most purposes) non-upgradeable NOR chip. With no valuable changeable
state in the device, the whole issue of recovering a bricked device
disappears, since you can just use a different/externally repaired

- Werner

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