Processor Stack; Stack Configurations - HP 9020 Service Manual

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Theory of Operation
Processor Stack
The processor stack is a 32-bit computer system that controls all computer operations. The stack
consists of an enclosing and supporting case, up to 12 boards, stack motherboard, and clock board.
The boards may be finstrates or polystrates.
Finstrates are copper-cored cards with NMOS-III chips bonded to them. Finstrates provide the
combined functions of cooling fins and ceramic substrates.
Polystrates (from polyimide and finstrate) are polyimide boards without the copper core. However,
copper heat sinks are mounted on the circuit side of the board, to dissipate heat from the chips.
All boards plug into the common Memory Processor Bus (MPB), provided on the mother board
(Figure 2-7).
The case has a door that can be opened to provide access to the upper 9 slots or removed to
provide access to all 12 slots. A dc box fan attached to one end of the stack provides cooling air to
the boards.
The stack interconnects with the computer motherboard via two 25-pin connectors and a 50-
conductor input/output processor (lOP) cable. The 25-pin connectors on the bottom of the stack
interconnect with connectors on the computer motherboard when the stack is positioned in the
computer. These connectors provide power and control signals. The internal lOP ribbon cable
connects to the lOP finstrate in slot #2.
Stack Configurations
The stack has 12 slots numbered from 1 to 12, with slot # 1 the bottom slot and slot # 12 the top. All
slots are interconnected by the memory processor bus via the stack motherboard. The Memory
Processor Bus (MPB), which has 32 data/address lines and 12 control lines, interconnects all boards
to the lOP finstrate(s). The lOP fin strate in slot #2 is connected to the internal lOP cable which is
routed to the motherboard.
Four types of boards can be used in the stack: central processor unit (CPU), input/output processor
(lOP), and random access memory (RAM). A load board may also be required, depending on stack
configuration. All are described in the following paragraphs.
The stack can be configured with various combinations of boards. One or two CPU finstrates can
be added. One or two lOP finstrates can be added. Any number of RAM boards are allowed.
However, if 1 Megabyte RAM boards are used, they must be used in pairs.
The following rules must be observed for all configurations:
• Slot # 1 must always contain a CPU finstrate.
• Slot #2 must always contain an lOP finstrate.
• If there is one additional lOP finstrate, it must be contained in slot #3. If there are two
additional lOP finstrates, they must be contained in slots #3 and #4.
• No empty slot is permitted between two finstrates.
• 1 Megabyte RAM boards must be used in pairs (2, 4,6,8, or 10).