I've been researching uses of the IBM 2315 disk pack design in various systems.
There appear to be two styles of sensors used for sector identification in IBM 2315 disk pack designs. The IBM 2310 disk drive used an optical sensor and notched-ring integrated into the spindle so that a U-shaped assembly of light+sensor is appropriately positioned when the pack is mounted (see: https://www.manualslib.com/products/Ibm-2310-10271354.html ). DEC also used this style in their RK05 drives (see: EK-RK5JF-MM-001_RKO5_RK05J_RK05F_Disk_Drive_Maintenance_Manual_Nov76.pdf, Figure 1-3 and Section 4.2.6 on page 4-16 (56-of-135) "an optical device that contains a light emitting diode and a photosensor". The other style utilizes a magnetic sensor and the hub (perimeter of the flat surface to which the pack is affixed when mounted) itself is notched. A flat sensor including a magnet is suitably positioned with respect to that face when the pack is mounted. HP used this style in their HP7906 drive, which combined a removable disk with a fixed disk (the fixed disk actually provided the sector-timing information for the removeable disk pack; the removeable disk itself only had a single index notch on the hub). I've become confused about the one used with Diablo Series 30 drives, typically employed by OEMs (e.g., Data General). I assume that it was one-or-the-other, but perhaps either might be used based on the requirement of a particular OEM? In D3140-171_Maintanance_Manual_For_Series-30_Disk_Drive_Jan72.pdf, on page 7-17 (92-of-103) Figure 7-9 SECTOR TRANSDUCER ASSEMBLY clearly illustrates the mechanism of a magnetic transducer, although nowhere can I find Series 30 technical documentation that specifically discusses the nature of its sector transducer. All schematics that I have checked do not seem to include any provisions for powering a light source, which is consistent with the use of a magnetic transducer. However https://www.righto.com/2018/03/a-1970s-disk-drive-that-wouldnt-seek.html from Ken Shirriff shows a Diablo drive where Ken clearly (https://lh3.googleusercontent.com/-_meZQXUR5NQ/Wr-34VTNwUI/AAAAAAABQe4/fhC1 75xg0Mcm6eeytILHMyUGZ1TFAUzkwCHMYBhgL/w9999/disk-opened.jpg) illustrates a disk pack that is hard-sectored based on slots-in-ring which AFAIK implies an optical sensor. He references 81503-02_Series_30_Disk_Drive_Maintenance_Nov75.pdf which is non-specific regarding the sector transducer, but on page 5-6 (41-of-63) it refers to there being "two interconnecting wires at the transducer" and Figure 5-7 SECTOR TRANSDUCER ADJUSTMENT appears to me to be consistent with the earlier maintenance manual Figure 7-9 SECTOR TRANSDUCER ASSEMBLY - a magnetic transducer. So is the opened disk pack not actually one for a Diablo Series 30 drive? Or did the Diablo Series 30 include an OEM-specific (?) variant that used an optical sensor? Or perhaps there's something else going on here with the various IBM 2315 disk pack designs regarding sector sensing that I fail to understand? ----- paul