Sun Microsystems and AT&T have released specifications for memory management units for use with Sparc microprocessors. The Reference MMU specification is designed to facilitate development of a range of high-performance single- and multi-chip memory managers and highly integrated single-chip versions of the Sparc. The other is Sun’s patented memory manager used in all its systems, and defines an expanded version of the Sun manager. It stores 64,000 simultaneous address translations, 1,000 times more than traditional memory managers. Both will be supported by Unix System V.4 for the Sparc; the Reference MMU is free to Sparc licencees, the second one will be licensed by Sun.