The VAX 9000 (codename "Aquarius" for the water-cooled variant or "Aridus" for the air-cooled variant) was an ECL implementation of the VAX architecture, positioned as a mainframe, or, with the optional vector processors installed, as a supercomputer, supporting up to 4 processors.

The CPU was implemented with 13 of these MCU's; each MCU contains a number of Motorola ECL macrocell arrays; the optional vector processor occupied 3 more MCA's. All 16 MCU's plugged into a 4 x 4 MCU planar module, measuring 63.5cm (25") on each side. The macro-cell arrays are put on a High-Density Signal Carrier (HDSC), built using wafer-fab technology, and consisting of 9 copper layers (4 power, 5 signal), separated by thin polyimide layers, and laminated onto a copper/nickel baseplate.

The chip in the center of the MCU is the clock distribution chip; surrounding it are 7 macrocell arrays, and 9 RAM chips. The pin fins on the back indicate that this module came from an air-cooled ("Aridus") system. A water-cooled MCU would have had attachment sites for water hoses here.

This hologram has been attached to an HDSC; on the back of the HDSC, the copper/nickel baseplate can be seen, with its characteristic chip site cutouts.