IBM 5162 Motherboard - Chips U27 and U81
U27
U81
Reverse engineering PAL chips
On the IBM 5152 motherboard, U27 and U81 are 'programmable array logic' (PAL) chips.
Chip U27
U27 is marked "59X7599". 59X7599 is the IBM part number. (Other IBM part numbers for this part may exist.)
IBM's circuit diagram for the IBM 5162 motherboard has U27 indicated as being type 20L8.
Content of the chip: {yet to locate} (the MAME project has this as file '59x7599.mmipal20l8.u27.jed')
Chip U81
U81 is marked "1503135". 1503135 is the IBM part number. (Other IBM part numbers for this part may exist.)
IBM's circuit diagram for the IBM 5162 motherboard has U81 indicated as being type HAL16L8A.
Content of the chip: 1503135.mmipal14l4.u81.jed (source: ibm5162.7z at here) (originates from the MAME project)
Reverse engineering PAL chips
In case of interest to you, a web page by Johann H. about reverse engineering PAL chips, is at here.