IBM 6643 - Manual (Page 22)

7. Lift the computer as shown and take care not to let the keyboard slide off the
base.
System board layout
3 2 1
1 Microprocessor connector
2 System fan connector (not used)
3 DIMM connectors
4 Power connector
5 Inverter connector
6 CD-ROM drive or DVD drive connector
7 Diskette drive connector
8 Hard disk drive connector
9 LCD connector
10 CMOS clear jumper
11 Battery
12 PCI expansion slot
13 PCI expansion slot
14 Reserved (not used)
15 CD-ROM or DVD-ROM audio connector
16 Speaker connector
17 USB connector
18 BTN (button) connector
19 IR (Infra Red) connector
20 Audio I/O and USB connector
21 CPU fan connector (fan located on EMC shield)
14 Hardware Maintenance Manual