What isbus and tag channel

Bus and Tag are old IBM standards that were used to connect mainframes to peripheral devices. They were typically used to connect devices such as line printers, disk storage, magnetic tape drives, and IBM 3270 display controllers. The interface consists of two sets of multi-terminated copper cables, one for data and the other for control information.

Bus and tag termination blocks

The cables are daisy-chained, and up to eight peripheral ECUs can be connected to one interface. The last control unit in the chain must have a terminating connector. Each control unit can have a maximum of 16 devices connected to it, and there is an architectural limit of 256 devices per channel. The data rates of the bus and tag channels can go up to 4.5 MB per second. However, only one device can transmit data at a time.

Bus and tag channel

Bus and Tag Channel is a general term used for the parallel channel between IBM mainframes and peripheral devices. This technology was also known as IBM’s OEMI interface.

Frequently Asked Questions (FAQ)

What is IBM OEMI interface?

IBM OEMI interface is another name for Bus and Tag Channel technology. It was mostly used for connecting IBM mainframes to various peripheral devices.

What is the limitation of devices that can be connected using Bus and Tag Channel?

The architectural limit of devices that can be connected using Bus and Tag Channel technology is 256 devices per channel.


Even though Bus and Tag technology is now considered old, it was a significant milestone in the history of peripheral devices and mainframes. Today, modern interfaces have replaced it, but it’s good to know where the technology started, and how it evolved over the years.

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