HP 50g Graphing Calculator - Manual (Page 770)

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Port 1 (ERAM) can contain up to 128 KB of data. Port 1, together with Port 0
and the HOME directory, constitute the calculator’s RAM (Random Access
Memory) segment of calculator’s memory. The RAM memory segment requires
continuous electric power supply from the calculator batteries to operate. To
avoid loss of the RAM memory contents, a CR2032 backup battery is included.
See additional details at the end of this chapter.
Port 2 belongs to the calculator’s Flash ROM (Read-Only Memory) segment,
which does not require a power supply. Therefore, removing the batteries of the
calculators will not affect the calculator’s Flash ROM segment. Port 2 can store
up to 1085 KB of data.
A fourth port, Port 3, is available for use with an SD flash memory card. An
example is shown below.
The port appears in File Manager only when an SD card is inserted.
The HOME directory
When using the calculator you may be creating variables to store intermediate
and final results. Some calculator operations, such as graphics and statistical
operations, create their own variables for storing data. These variables will be
stored in the HOME directory or one of its directories. Details on the
manipulation of variables and directories are presented in Chapter 2.
Port memory
Unlike the HOME directory, the memory in ports 0, 1 and 2 cannot be sub-
divided into directories, and it can only contain backup objects or library
objects. These object types are described below.