Editing IBM 305 RAMAC (section)

===Timing===
All timing signals for the 305 were derived from a factory recorded ''clock track'' on the drum. The clock track contained 816 pulses 12&nbsp;μs apart with a 208&nbsp;μs gap for sync.

Reading or writing a character took 96&nbsp;μs.

The 305's typical instruction took three revolutions of the drum (30&nbsp;ms): one (''I phase'') to fetch the instruction, one (''R phase'') to read the source operand and copy it to the core buffer, and one (''W phase'') to write the destination operand from the core buffer. If the P field (Program exit code) was not blank, then two (''D phase'' and ''P phase'') additional revolutions of the drum (20&nbsp;ms) were added to the execution time to allow relays to be picked. The ''Improved Processing Speed'' option could be installed that allowed the three instruction phases (''IRW'') to immediately follow each other instead of waiting for the next revolution to start; with this option and well optimized code and operand placement a typical instruction could execute in as little as one revolution of the drum (10&nbsp;ms).

Certain instructions though took far longer than the typical 30&nbsp;ms to 50&nbsp;ms. For example, multiply took six to nineteen revolutions of the drum (60&nbsp;ms to 190&nbsp;ms) and divide (an option) took ten to thirty seven revolutions of the drum (100&nbsp;ms to 370&nbsp;ms). Input/Output instructions could interlock the processor for as many revolutions of the drum as needed by the hardware.