6 ms·

For variable number of sectors per cylinder you either need control over bitrate or motor speed.

by rasz 3y ago

somat 3y ago
Not an expert, I just read the datasheet but the format command takes The number of data bytes written in a sector Sectors per Cylinder Gap Length Data Pattern Then while the command is executing it takes(or might give... I am not real clear on this part) Cylinder Number Head Number Record The number of data bytes written in a sector So the hacker in me says why cant you say you want to format the disk then only format one cylinder. then do it again with another cylinder but this time with a different number of sectors. Reading and writing such a franken disk is left as an exercise for the reader. Honestly the whole exercise might be a fun weekend messing with assembly trying to see what contortions you could get the disk controller to do. It also sounds like a huge pain, I think I would want some sort of low level "stub" os, that does nothing bet gets the system initialized in a known state. then you could proceed to engage in severe sadomasochism, locking up your system in strange and mysterious ways.
- rasz 3y ago
  This will just make gaps between sectors bigger, lowering capacity given standard bitrate and rotation speed. The point of zone bit recording (ZBR) / zoned constant linear velocity (ZCLV) is to pack mode data on the outside (longer) cylinders. Doing some back of napkin calculations the most Outer track has circumference of ~27 cm while inner is ~18cm long. Outer track should be able to fit 1.5 x magnetic flips while staying in spec. If you want even more data you go GCR all the way to RLL encoding. Fantastic dev blog documenting implementation of 3.5 Inch HD (2.7)RLL Floppy Controller for use in MEGA65 project: https://c65gs.blogspot.com/2022/01/more-work-on-hd-floppies-rll-encoding.html https://c65gs.blogspot.com/2022/01/more-work-on-hd-floppies-... Over 3MB out of standard 1.44MB drive/floppy by combining both zone recording and RLL.

For variable number of sectors per cylinder you either need control over bitrate or motor speed.

by rasz 3y ago

For variable number of sectors per cylinder you either need control over bitrate or motor speed.

Not an expert, I just read the datasheet but the format command takes The number of data bytes written in a sector Sectors per Cylinder Gap Length Data Pattern Then while the command is executing it takes(or might give... I am not real clear on this part) Cylinder Number Head Number Record The number of data bytes written in a sector So the hacker in me says why cant you say you want to format the disk then only format one cylinder. then do it again with another cylinder but this time with a different number of sectors. Reading and writing such a franken disk is left as an exercise for the reader. Honestly the whole exercise might be a fun weekend messing with assembly trying to see what contortions you could get the disk controller to do. It also sounds like a huge pain, I think I would want some sort of low level "stub" os, that does nothing bet gets the system initialized in a known state. then you could proceed to engage in severe sadomasochism, locking up your system in strange and mysterious ways.

rasz 3y ago
This will just make gaps between sectors bigger, lowering capacity given standard bitrate and rotation speed. The point of zone bit recording (ZBR) / zoned constant linear velocity (ZCLV) is to pack mode data on the outside (longer) cylinders. Doing some back of napkin calculations the most Outer track has circumference of ~27 cm while inner is ~18cm long. Outer track should be able to fit 1.5 x magnetic flips while staying in spec. If you want even more data you go GCR all the way to RLL encoding. Fantastic dev blog documenting implementation of 3.5 Inch HD (2.7)RLL Floppy Controller for use in MEGA65 project: https://c65gs.blogspot.com/2022/01/more-work-on-hd-floppies-rll-encoding.html https://c65gs.blogspot.com/2022/01/more-work-on-hd-floppies-... Over 3MB out of standard 1.44MB drive/floppy by combining both zone recording and RLL.