ounted for. These extra control bits add up to fairly significant overhead. In essence, asynchronous transmission has 30% inefficiency because for every seven bits of information, there are at least three bits of control, and it can be higher as there can be 1, 1.5, or 2 stop bits used. Another disadvantage of asynchronous transmission is that it operates at comparatively low speeds; today, in general, it operates at no higher than 115Kbps. Synchronous transmission emerged in the late 1960s, when IBM introduced its interactive processing line, which included smart terminals. These smart terminals could process information and use algorithms; for example, a terminal could use an algorithm on a message block to determine what it was composed of and in that way very succinctly check for errors. Smart terminals had buffers, SO they could accumulate the characters being typed in until they had a big block that they could send all at one time. Smart terminals also had clocking devices, whereby on one pair of wires, a clocking pulse could be sent from the transmitter to the receiver. The receiver would lock in on that clocking pulse, and it could determine that with every clocking pulse it saw on one wire, it would have a bit of information present on the other wire. Therefore, the receiver could use the clocking pulse to simply count off the bits to determine where the beginning and the end of the character were, rather than actually having to frame each character with a start bit and a stop bit. Synchronous transmission in classic data communications implied sending information a block at a time at a fixed speed. Data Flow Another benefit of synchronous transmission is very tight error control. As mentioned earlier, smart terminals have processors and can apply mathematical algorithms to a block of data. By calculating the contents of that block, the termi- nal comes up with a 16- or 32-bit code that identifies the structure of the block's contents. The terminal adds this code to the end of the block and sends it to t