Editing Data General Nova (section)

====Nova 4====
It appears that Data General originally intended the Nova 3 to be the last of its line, planning to replace the Nova with the later Eclipse machines.{{citation needed|date=March 2024}} However, continued demand led to a '''Nova 4''' machine introduced in 1978, this time based on four [[AMD Am2901]] [[bit-slice]] [[arithmetic logic unit|ALUs]]. This machine was designed from the start to be both the Nova 4 and the Eclipse S/140, with different [[microcode]] for each. A floating-point co-processor was also available, taking up a separate slot. An additional option allowed for memory mapping, allowing programs to access up to 128&nbsp;kwords of memory using [[bank switching]]. Unlike the earlier machines, the Nova 4 did not include a [[front panel|front panel console]] and instead included a ROM containing machine code that allows a [[computer terminal|terminal]] to emulate a console when needed.<ref name="nova-4-fe-manual">{{cite book|url=http://www.bitsavers.org/pdf/dg/Nova_4/015-000095-02_Nova_4_Field_Engineering_Reference.pdf|title=Nova 4/S and 4/X|series=Field Engineer's Reference Series|date=June 1981|publisher=[[Data General]]}}</ref>{{rp|page=87}}

There were three different versions of the Nova 4, the Nova 4/C, the Nova 4/S and the Nova 4/X. The Nova 4/C was a single-board implementation that included all of the memory (16 or 32&nbsp;kwords). The Nova 4/S and 4/X used separate memory boards. The Nova 4/X had the on-board [[memory management unit]] (MMU) enabled to allow up to 128&nbsp;kwords of memory to be used. The MMU was also installed in the Nova 4/S, but was disabled by firmware. Both the 4/S and the 4/X included a "prefetcher" to increase performance by fetching up to 11 instructions from memory before they were needed.<ref name="nova-4-fe-manual" />{{rp|page=5}}