Editing IBM 709 (section)

==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 the 704 is a programmed function of the central processor - data words are transferred to or from the I/O register, one at a time, using a "copy" instruction - the 709 uses the IBM-766 data synchronizer, which provides two independently "programmed" I/O channels. Up to three Data Synchronizers can be attached to a 709, each able to control up to 20 [[IBM 729]] tape drives and an [[IBM 716]] alphanumeric line printer, [[IBM 711]] card-reader and 721 card punch. This allows six times as many I/O devices on the 709, and allows I/O to proceed on multiple devices while program execution continues in parallel. Up to two IBM 733 [[Drum memory|Magnetic Drum]] units, each with 8,192 words of memory, could be attached independently from the Data Synchronizers.  The 709 could initially load programs ([[booting|boot]]) from card, tape or drum.<ref name=709refman />{{rp|113}}

The [[IBM 738]] Magnetic Core Storage used on the 709 was also a milestone of hybrid technology. Although the core array drivers all used vacuum tubes, the read sense amplifiers were a very early use of transistors in computing.