I/O Channel
The primary improvements of the 709 over the previous 704 involved more magnetic core memory and apparently the first use of independent I/O channels. Whereas I/O on 704 was a programmed function of the central processor - data words were transferred to or from the I/O register, one at a time, using a "copy" instruction - the 709 came with the IBM-766 Data Synchronizer, which provided two independently "programmed" I/O channels. Up to three Data Synchronizers could be attached to a 709, each able to control up to 20 tape drives and a card-reader/punch/printer set. This allowed six times as many I/O devices on 709, and allowed I/O to proceed on multiple devices while program execution continued in parallel.
The IBM-738 Magnetic Core Storage used on 709 was also a milestone of hybrid technology. Although the core array drivers were all vacuum tube, the read sense amplifiers were a very early use of transistors in computing.
Read more about this topic: IBM 709
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