Radio Shack TRS-80 Model 100 Basic Manual page 121

Experiment #4 Available Memory
The Model 100 has many other useful functions built into it besides square root,
tangent and arctangent. While some of these are mathematical in nature, others are
more general. For example, the
FRE
function lets you determine the amount of
available memory and, indirectly, the amount of memory used by your BASIC
program.
To see how much memory you currently have available, type:
PRINT FRE(0) ~
The number which is displayed, such as
28265
will depend upon several factors, including how much RAM is installed in your
Computer, how many files you have saved, and how large the current BASIC program
is. The argument (within the parentheses) used with the PRE function can be a
numeric constant, variable or expression. The PRE function will always return the
amount of available memory regardless of the value of the argument. To verify this,
type:
PRINT FRE(10) ~
and you should see the same value displayed as before.
To determine the amount of memory used by a BASIC program, type:
PRINT FRE(0) ~
before you begin typing your program. Then, after having typed it, type:
PRINT FRE(0)
(ENTER)
again. This will print the amount of memory left or unused by your program. Finally,
subtract the amount you obtained initially from the amount of memory after the
program was typed. The number obtained is the number of bytes used by the program.
Experiment #5 String Space
The PRE function may also be used to determine the amount of memory available to
store strings. Type:
PR I NT FRE ( "
II )
CEJIT.EID
and you should see:
256
which indicates that 256 bytes of memory have been allocated for the storage of
strings. The PRE function will return available string space if the argument is any
string constant (such as the null string'" '), string variable, or string expression.
Verify this by typing:
PRINT FRE ("ABC")
CE8.LEID
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