GA22-7000-10 IBM System/370 Principles of Operation Sept 1987
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Control General Floating-Point Registers Registers Registers R Register Field Number 1+--32 1+--32 1 64 bits 0000 0 [I I 0001 1 0010 2 [I 0011 3 I [I 0100 4 I 0101 5 [I 0110 6 I 0111 7 1000 8 [I 1001 9 I [I Note: The brackets 1010 10 indicate that the two registers may be coupled as a double-register I pair, designated by 1011 11 specifying the lower- numbered register in the R field. For ex- [I ample, the general- 1100 12 register pair 14 and 15 is designated by 1110 binary in the R I field. 1101 13 [I 1110 14 I 1111 15 General, Floating-Point, and Control Registers Chapter 2. Organization 2-5
CHANNEL SETS The group of channels which connects to a particular CPU is called a channel set. When channel-set switching is installed in a multiprocessing config uration, the program can control which CPU is connected to a particular channel set. A CPU can be connected to no more than one channel set at a time, and a channel set can be connected to no more than one CPU at a time. When channel set switching is not installed, the channel sets, in the absence of model dependent reconfiguration controls, are permanently connected to a single CPU. CHANNELS A channel relieves the CPU of the burden of communicating directly with I/O devices and permits data processing to proceed concurrently with I/O operations. A channel is connected with main storage, with control units, and, unless it is a member of a disconnected channel set, with a cpu. A channel may be an independent unit, complete with the necessary logical and internal-storage capabilities, or it may time-share CPU facilities and be phys ically integrated with the CPU. In either case, the functions performed by a channel are identical. The maximum data-transfer rate may differ, however, depending on the implementation. There are three types of channels: byte-multiplexer, block-multiplexer, and selector channels. 2-6 System/370 Principles of Operation I/O DEVICES AND CONTROL UNITS I/O devices include such equipment as card readers and punches, magnetic-tape units, direct-access storage, displays, keyboards, printers, teleprocessing devices, communications controllers, and sensor-based equipment. Many I/O devices function with an external medium, such as punched cards or magnet ic tape. Some I/O devices handle only electrical signals, such as those found in sensor-based networks. In either case, I/O-device operation is regulated by a control unit. In all cases, the control-unit function provides the logical and buffering capabilities necessary to operate the associated I/O device. From the programming point of view, most control-unit functions merge with I/O-device functions. The control-unit function may be housed with the I/O device or in the CPU, or a sepa rate control unit may be used. OPERATOR FACILITIES The operator facilities provide the functions necessary for operator control of the machine. Associated with the operator facilities may be an operator console device, which may also be used as an I/O device for communicating with the program. The main functions provided by the oper ator facilities include resetting, clearing, initial program loading, start, stop, alter, and display.