Lesson 12: understanding memory – HP 48G User Manual
Page 46
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Lesson 12: Understanding Memory
Thus far it. has been convenient to think of the HP 48 as a
calculator—albeit
an advanced
calculator. However,
when considering
its memory, it is better to think of it as a computer.
The basic unit of storage on a desktop computer is the
n a m e d f i l e .
On
the HP 48 the basic unit of storage is the named object, or
v a r u i h l e .
Unnamed objects can exist on the stack, but, like computer files, must
be
named in
order
to
be
saved. Envision a variable
as a named storage
area containing an olfiect.
Variables,
reflecting the
objects
they
contain, vary widely in both
size
and type. Like
stored
computer
files,
variables
are organized
into
d i r e c t o r i e s
—“file folders”—that make it convenient to find them later.
Example:
Determine the amount of memory (in bytes) currently
available to store HP 48 variables.
Variables on the HP 48 are stored in SYSRAM—or on a plug-in card
in the case of the expandable HP 48 models. SYSRAM memory is like
a desktop computer’s
Random-Access-Memory
(RAM) except that it
is
n o n - v o l a t i l e
—it isn’t erased when the HP 48 is turned off.
The figure below shows how the HP 48 divides up the SYSRAM and
the type of variables (in parentheses)
stored
in each section:
Partitions move depending on current allocation of memory
System ; Available Memory
Stack I Program | User
Port 0
(system) j
I (local)
I (global)
(port)
Schematic view of SYSRAM in the HP 48
4-2 Understanding and Using Memory