VLSI VI475

The VLSI VI475, also known as Apple HMMU or HMMU Chip, is a hardware memory management unit (HMMU) that was custom produced by for Apple Computer to use in its Macintosh II computer. Its Apple part number is 343-0002-1. by Gona.eu, Wikimedia Commons. 2009-05-08 / 2009-04-19. The chip has also been referred to as the "Hochsprung Memory Management Unit" after Ron Hochsprung, one of the system architects of the Macintosh II.The Logic Board (PDF) by Mark D. Veljkov, The Macintosh II Reference Guide p.17. Scott, Foresman and Company. 1989.Ronald Hochsprung (CS ’72), Illinois Institute of Technology. Accessed 2021-03-03.The Making of the Macintosh II by Steven Levy, Macworld. 1987-01.
==Features==
The VI475 added backwards compatibility for 24-bit addressing to the 68020 processor because the ROMs in the Macintosh II were not yet 32-bit clean. However, it did not include paged memory management functionality required for virtual memory support like the more expensive 68851.
The VI475 uses only 70 out of the 132 pins in a 68851 socket and can be swapped for a full 68851 to add support for virtual memory, 32-bit addressing (with MODE32 and a FDHD ROM upgrade), and A/UX. by Gona.eu, Wikimedia Commons. 2009-05-08 / 2009-04-19. These memory management features were later built directly into the 68030 processor used by subsequent Macintosh II series models.Frequently Asked Questions (FAQ) by Robert Boys, comp.sys.m68k. 1996-01-06.
==History==
A prototype version of the Macintosh II, code named "Paris", used a custom hardware memory management daughtercard as a predecessor to the VI475. This daughtercard occupied the 68851 socket and contained three Programmable Array Logic (PAL) chips produced by . This was consolidated into the VI475 upon release of the Macintosh II to the public.“Paris” Prototype Apple Macintosh II Motherboard by Plocmstart! 2017-04-08.
==References==
==External links==
*What was the design of the Macintosh II's MMU replacement? at StackExhange (2019-05-01)
*Explanation of Macintosh II's memory limit at 68k Macintosh Liberation Army (2016-04-24)
* at Wikipedia