Does iOS support virtual memory and a swap file?

From +Memory Usage Performance Guidelines+

Both Mac OS X and iOS include a fully-integrated virtual memory system that you cannot turn off; it is always on. Both system also provide up to 4 gigabytes of addressable space per 32-bit process. In addition, Mac OS X provides approximately 18 exabytes of addressable space for 64-bit processes. Even for computers that have 4 or more gigabytes of RAM available, the system rarely dedicates this much RAM to a single process.

To give processes access to their entire 4 gigabyte or 18 exabyte address space, Mac OS X uses the hard disk to hold data that is not currently in use. As memory gets full, sections of memory that are not being used are written to disk to make room for data that is needed now. The portion of the disk that stores the unused data is known as the backing store because it provides the backup storage for main memory.

Although Mac OS X supports a backing store, iOS does not. In iPhone applications, read-only data that is already on the disk (such as code pages) is simply removed from memory and reloaded from disk as needed. Writable data is never removed from memory by the operating system. Instead, if the amount of free memory drops below a certain threshold, the system asks the running applications to free up memory voluntarily to make room for new data. Applications that fail to free up enough memory are terminated.

Create an app that allocates a gigabyte of RAM and see what happens.

If so, does it mean that my app can "hypothetically" allocate 1GB of space in perfect conditions?

Allocate, yes, use NO!

iOS does not have a swap file, right?

Right.

Hey! You are the same person asking about initWithCapacity in the other thread. Now we know what you are up to 🙂

What is taking so much memory? You have a fast processor and fast storage. Just load your data on demand. If it doesn't run fast enough, create a simple caching mechanism. I bet that loading your data dynamically is going to yield better performance than asking the OS to shuffle everything around.

Yea, I was wondering the same. Everything I have read suggests executable code is paged, and the iOS supports swapping but that it is disabled to avoid thrashing the Flash storage, and the app is expected manage its own resources which makes sense and is probably a good idea (since you know what mem is readonly/readwrite, and what should be specifically cached when..). There is also NSData initWithContentsOfMappedFile: which may be of use in some situations. But I also want to know how much actual RAM I can use, and if having many other BG Apps decreases this. I tried the following code:

for (int i=1; malloc(1024); i++)
if (!(i % 1024))
printf("malloc: %f MB\n", i/1024.);

which returns ~600 MB on both iPod 3rd and 4th gen (and regardless of if 100 apps are in BG or none). But both of these devices should be only 256 MB, so I must have something wrong in this code right?