SAP Roll Area 
The roll area is a memory area with a set (configurable) size that belongs to a work process. It is located in the heap of the virtual address space of the work process.
When the context of a work process changes, the data is copied from the roll area to a common resource known as the roll file. To prevent repeated copying, another roll buffer is located in between, which is part of the shared memory.
Structure
The roll area consists of two segments. The first segment, which can be set with the parameter ztta/roll_first, is assigned to the work process first as memory. If this is used up, the work process has more memory assigned to it. The amount of memory is determined by the difference between the ztta/roll_area and ztta/roll_first parameters.
For more information, see the platform-specific section under Implementation.
Note
For technical reasons, the roll area is always the first memory to receive a work process. Only afterwards can extended memory be requested.