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Input/Output Descriptors

An Input/Output descriptor consists of a variable number of six-digit syllables. Most of the inptu/output descriptors contain one, two or three syllables depending on the specific I/O operation requirements. Disk file I/O descriptors contain four syllables.

B2500/B3500 Input/Output Descriptor

Digits D1 and D2 always specify the type of I/O operation to be performed. Digits D3 through D6 specify which of the various options the specific I/O operation may incorporate. The second syllable will contain the addres sof the most significant digit of the input or output core memory buffer area. This is also called the beginning address and must be synchronized modulo four, i.e. it must begin on a word boundary. The third syllable contains the address of the least significant digit plus one. This address is called the ending address and is actually the address of the first digit in the field immediately following the input/output buffer area. Magnetic tape, Disk File, sorter-reader and lister descriptors require the ending address to be synchronized modulo four. This address must be modulo two (even) for all other I/O descriptors.

Disk file descrxiptor require four syllables. The last syllable contains the disk file address. All beginning and ending addresses used in I/O descriptors are always absolute 6-digit addresses. Any I/O operation that attempts to access memory behond the ending address will inhibit a memory transfer. Each type of I/O operation will generate a result descriptor. The result descriptor contains information pertinent to the type of I/O operation, including normal or non-normal execution.

dlps/io_descriptor.1549219234.txt.gz · Last modified: 2019/02/03 10:40 by scott
 
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