3 Memory

The real HP-42S has about 7200 bytes of memory while Free42 can have much more depending on the available memory in the computer/handheld.

In fact, 7200 bytes is a lot of memory for HP-42S! A program of 10 lines uses about 15 bytes of memory. This means that while in some other models like HP-20S you would be able to program just 99 lines with 42S you would be able to create programs with thousands of lines!

This available memory is shared with everything including programs, variables, etc.

Let's start from the basic. To store a number which is in line x of the stack we use STO function.

The HP-42S has by default 25 positions in the memory from R00 to R24. To store the number π in R10 is just do the following

▀π STO 10 To get it back it is just do this

RCL 1 0

If you want to make an operation you can use STO+, STO-, STOx, STO÷. For example, 6 STO- 0 5 subtracts 6 from the number in R05.

2 STO ÷ 1 0 divides the number in R10 by 2.

You can also use RCL+. RCL-, RCLx, RCL÷, but it is not so fun. This gives the result of the calculation but does not change the number in the memory.

If 25 positions in the memory is not enough for you, you can change this number by using SIZE function (which is in the second line of MODES menu).

For example ▀ MODES ▼ SIZE 0 1 0 0 changes to have 100 positions, from R00 to R99.

Despite it is possible I suggest you to not use more than 100 positions. These positions are stored in a normal matrix called REGS.

(We, the poor owners of HP-33S for example, just have 26 memory positions, from A to Z)

But this kind of memory position only accept real numbers! What about if you want to store other things? Matrices, complex numbers of even other real numbers?

To do this HP-42S has an arbitrary number of positions limited only by the memory available which uses letters to label instead of numbers.

We had stored the π number in R10 but we can create a variable called for example “PI” to store it.

It is just to do

▀ π ENTER STO ▀ ALPHA “PI” ENTER.