IOCF terminology

Device number

Each I/O device is identified in the IOCF by a unique device number (0000-FFFF). During generation, this device number (four hexadecimal characters) is derived by IOGEN from the mnemonic (two alphanumeric or four hexadecimal characters) for each device.

The 4-character mnemonic, whose first character may not be zero, is used as the device number.

Mapping of the 2-character mnemonic to the device number (with a leading zero) is performed in accordance with the following algorithm:

1. The mnemonic is converted into a 16-bit string.

2. Bits 2⁶, 2⁷ and 2¹⁴, 2¹⁵ are deleted.

3. The 12-bit strings thus created are converted to hexadecimal characters with a leading zero.

Example

Mnemonic	Conversion process	Device number
C'10A1'		X'10A1'
C'M1'	X'D4F1' B'1101 0100 1111 0001'   eliminate B'0101 0011 0001'	X'0531'

For the exact assignments of mnemonics to device numbers, refer to the allocation table on "Allocation table: mnemonic name - device number". To simplify matters, we recommend that you assign four-digit mnemonics to disk devices.

In the case of an IPL the device number of the IPL device must be specified.

Subchannel number

The subchannel number refers to an internal numbering system by which all I/O devices are identified. A subchannel represents a device (DVC).

Subchannel numbers are assigned by IOGEN without a gap, starting at zero.

Control unit number

The control unit number represents a hardware controller. It is 16 bits long and, like the device number, is derived from the controller’s mnemonic.

Channel Control Unit Connection (CCUC)

The Channel Control Unit Connection (CCUC) represents a connection between controller and channel. A CCUC entry is created for each of these connections in the IOCF.

Communication Path Group (CMPG)

A Communication Path Group (CMPG) is a system-internal structure which comprises up to eight CCUCs. The CMPG numbers are assigned by IOGEN without a gap starting with zero.

Each device is assigned to precisely one CMPG. This CMPG must contain all controller channel ports for this device.

A CCUC may reside in only one CMPG. Here all controllers which are linked by jointly used devices are included in a CPMG with their channel ports.

A CMPG is thus the logical representation of the following controller types:

• A controller whose connected devices have no further controller ports on this server.

• Two to eight controllers which are interconnected by jointly used devices.

However, no more than eight CCUCs may be defined in a CMPG.