COS310/WPS278 floppy images?

[AK6DN]

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The first thing to notice is that only 12 bits of every 16 is used in an RX50, while an RX01 uses all bits by dividing 256 12-bit words among 3 128-byte sectors (words 0-127 low-order 8 bits in one sector, words 128-255 low-order 8 bits in the next, and the the high-order 4 bits for all 256 words in the third sector. Interleave on RX50 is 2:1 with a track skew, RX01 is a 3:1 interleave with no skew.

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So this is completely different than how an RX01/RX02 drive itself implements 12b vs 8b mode storage on RX01 or RX02 media.

In 12bit mode in the RX drive controller, each three consecutive 8bit media storage bytes (totaling 24bits) is then used to store two 12bit words.
Only 3/4 of the media storage density is used in each mode, storing 64 12bit words (needing 96 8bit bytes). The last 32 8bit bytes of the sector are zeroed/ignored.
For the RX02 with 256 byte sectors the numbers are doubled vs the RX01 (ie, 128 12bit words needing 192 8bit bytes, the last 64 8bit bytes zeroed/ignored).

So I guess then WPS278 would use the RX01/RX02 drives in 8b mode and do the 8b to 12b packing/unpacking in the driver?

That is more efficient usage of the storage (ie, 100%) than OS8 (75%) so that is a win. OS8 disks could still be accessed, but would require additional code to emulate the drive 12b behavior.

 

[Chuck(G)]

Exactly. I guess that the tradeoff in speed vs. storage was less important in the case of WPS. Dan Bricklin may recall what it was done that way. The interesting thing is that the RX50 in MFM stores about the same amount of data as an RX01 in FM mode for WPS.

 

[hush]

unfortunately i won't be able to test any images as my dmii has stopped booting valid images, gonna see about fixing it this week