apps.AppDB

The MemoryInfo (TM) app shows how much memory is available and the types of memory on your iPhone or iPod Touch.
It also shows your current battery level in percent.

The iPhone and iPod Touch comes with 128MB of runtime memory while the iPhone 3GS comes with 256MB of runtime memory. The iPhone 4 has 512MB of RAM. That is different from the 8GB, 16GB or 32GB of storage memory that the iPhone or iPod Touch has. The iPhone and iPod Touch does not use the storage memory as virtual memory, so the memory available for applications is limited to the 128-512MB of runtime memory.

Memory types:

Free memory
This memory is not being used currently

Wired memory
This information can't be moved to disk, so it must stay in RAM. The amount depends on the applications you are using.

Active memory
This information is currently in RAM and has recently been used.

Inactive memory
This information has not recently been used but will remain in RAM until another application needs more memory but no free memory is available. If called upon by a process, this is quickly changed to Active memory; if it has been swapped to the hard disk, it will be moved back to RAM and marked as Active.

Page ins / Page outs
"Page ins/outs" refers to the amount of information moved between RAM and the hard disk. This number is cumulative amount of data that iPhone OS has moved between RAM and disk space.