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Inside an IBM/Motorola mainframe controller chip from 1981
In this article, I look inside a chip in the IBM 3274 Control Unit. 1 But before I discuss the chip, I need to give some background on main...
The Control Unit was connected to the mainframe's channel processor which handled I/O by moving data between memory and peripherals without slowing down the CPU. The Texas Instruments ICs in the upper right are easier to identify; the 74LS641 chips are octal bus transceivers, presumably connecting this board to the rest of the system. However, performance is limited by the relatively weak pull-up current, making bus lines slow to go high due to R-C delays.
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