The connections to the central processor complex are made in a physical area of the processor frame called an I/O cage. Within the cage, OSA cards and memory modules (and other devices) are physically attached to the central processor complex. Parallel, FICON and ESCON connections are all made within the cage as well, using an adapter card.

Figure 1 shows a photograph of an I/O cage. The two cards with numerous small black fiber channel connectors are ESCON cards. The next card to the right is an OSA card, with two RJ-45 connectors. The cards connected to the large black cables are inter-system coupling (ISC) cards for coupling links. To the far right of the image is another ESCON card with several fiber optic cables connected to it.

Figure 1. I/O cage