IBM i series Handbook page 290

Towers and Racks
When upgrading to a Model 840 from a Model 650, S40, or 740, the #9251 Base I/O Tower on
these models is converted to the #5077.
When upgrading to a Model 840 from a Model 820 or 830 with #5034 or #5035 Migration
Tower I, which has SPD cards or SPD towers attached, the #5077 is a manufactured unit and
is shipped without a base CD-ROM and with a base optical link card (CCIN 2696).
One or two #2695 Optical Bus Adapters features may be ordered for the #5077.
If a #5077 is a manufactured unit, it ships with a CCIN 671A MFIOP. If the #5077 is converted
from a #9251, the base MFIOP is replaced by the CCIN 671A MFIOP. The CCIN 671A MFIOP
controls the disk units in the #5077 and the #5057, and removable media devices in the
#5077.
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iSeries Handbook