Question

For my understanding there are always two types of memory:

• the working storage

• the “disk space”

So when you have a 16 GB iPhone, does it have 16 GB of working storage? or 16 GB of “disk space”? Which “Memory” is Apple talking about in his Docs, when it comes to performance and memory management? It looks like the working storage, but I am not sure. Actually I thought the iPhone is a huge brick of working storage, since all that stuff is just a solid block of chip memory (no hard drive).

Answer 1

The iPhone has 16GB (or 8 or 4, depending on the model) of non-volatile flash memory that persists even when the power is turned off. It also has 128MB of volatile DRAM that gets lost when the power is turned off. The relative differences are:

• Flash memory is cheap, DRAM is expensive
• Flash memory is slow, DRAM is fast
• Flash memory is non-volatile, DRAM is volatile

The flash memory is essentially like a hard drive, except it’s a solid-state memory, not a rotating platter of magnetic dipoles.

Generally, in iPhone development, when you’re talking about memory, you’re talking about DRAM. DRAM is a more limited resource and more likely to run out, since it’s very easy for an app do eat up megabytes by poor memory management. It’s a lot harder to run out of flash memory, since doing so would involve writing very large files into the file system.