I/O Priority Assignment; Figure 2-7. Hp 2959/2999 Cards And I/O Priority Assignments - HP 1000 A990 Installation And Service Manual

I/O Priority Assignment
Each peripheral device in the system must be connected to the computer system through an
interface card installed in the card cage. A priority chain connects all interface cards in series to
prioritize simultaneous DMA requests and interrupt requests from two or more peripherals. The
priority of an interface card is determined by the slot the card occupies, with the slot directly
after the last memory card having the highest priority and slot 20 having the lowest priority. See
Figure 2-7 for an illustration of the I/O priority assignments. Configuring I/O priority consists of
installing interface cards in the desired order of priority.
I/O requests from a higher priority device inhibit lower priority requests by breaking the priority
chain. To maximize system response time and efficiency, assign the higher priorities to high-speed
peripherals. Consult the system manager to establish I/O device priority and install the interface
cards accordingly.
Note
Correct computer operation requires that there be NO vacant slots
between plug-in cards.
"
Cable to I/O Device
with Lowest Priority
Memory Array
Card
Cable to I/O Device with
Highest Priority
(System Disk Drive)
Figure 2-7. HP 2959/2999 Cards and I/O Priority Assignments
Memory
Frontplane
Connector
A990 CPU
Card
Installation 2-9