rdisp/max_alt_modes is a SAP Parameter attribute which is used to control Maximum number of alternative modes information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
You can use this parameter to restrict the maximum number of sessions
that an SAP GUI user can open per logon. However, you should only change
this if the circumstances require it (for example, if there are too many
sessions or not enough free session memory). Note that in certain
situations the system may automatically create new, hidden sessions (for
example, for front-end printing). You can change the parameter
dynamically. The changes apply for all logons that occur after the
parameter change.
Caution
Up to and including release 6.10, SAP GUI can display a maximum of 6
external sessions. In all newer releases, you can configure a maximum of
16 sessions. If you want to set the parameter to a value higher than 6,
you therefore require a SAP GUI of release 6.20 or higher.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.