Singer 40 - Consecutive Read;Write Operation Timings; Overlap Timings and Computational Impact

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Timing Considerations
After reading or writing a sector, the first subsequent sector on the same track
which may be read or written without requiring an additional revolution of the
disc is the fifth sector following the one read or written. Notice that the disc is
formatted such that sector 2 is the fifth sector following sector 1, sector 3 is
the fifth sector following sector 2, etc. This means that it is very efficient to
read and write a series of consecutively numbered sectors.
When performing any of the pairs of read/write operations shown in Table 7-2
using consecutively numbered sectors (e.g., sectors 1 and 2, 48 and 49, etc.) on
the same track, it takes 2 ms. for the second sector to move to the read/write
heads after the first operation is finished. If the two disc I/O instructions are
executed consecutively, the entire 2 ms. is wasted time. However, if computa-
tional instructions are inserted between the two disc I/O instructions, the
amount of time wasted can be significantly reduced. The figures shown in the
right column of Table 7 -2 specify the absolute maximum amount of time avail-
able for computation be~een the two disc I/O instructions. If the times are
exceeded, an additional revolution of the disc (25 ms.) will be required for the
second operation.
Table 7 -2. Overlap Timings
Read
Re!:lrl
.-., ---
Write
Write
Write
Read
Read
Write
1.6 ms.
.6 ms.
1.6 ms.
.6 ms.
NOTE: The Disc Controller takes 1 ms. to perform the special timing
algorithm at the start of a write operation. Therefore, only 0.6 ms. is
available for computation when a Write instruction is the second in the
pair of disc I/O instructions.
Models 40 to 42 Reference Manaul 7-3