1. A computer system comprising: one or more system-managed registers, each of the one or more system-managed registers having a register state indicating whether the one or more system-managed registers are free or busy; software configured to access the one or more system-managed registers only indirectly via a register index, wherein the register index can be obtained by the software only via checking the register state of the one or more system-managed registers; a first instruction configured to provide an index of one of the one or more system-managed registers with a free register state; and a number-providing instruction configured to provide a number indicating how many of the one or more system-managed registers have a busy register state.