Build 1.5 Mb disk drive?

[Thomas]

2*160*11*512

In fact it is 2*80*22*512 resp. 2*80*18*512. "High density" does not mean twice as any tracks but the same number of tracks with twice as many sectors each.

Bye,
Thomas

[Thomas]

Kronos wrote:
The extra space was gained be replacing MFM with something mor
efficient.

You could probably pack up to 1.4 MB onto a DD floppy if you use GCR encoding instead of MFM (GCR uses five bits per nibble while MFM uses eight bits). The Amiga floppy controller is able to handle this, you don't need extra hardware. You have to write your own floppy driver, though.

Bye,
Thomas

[Thomas]

That's correct, it did access at half speed, which is why using high-density disks in the Amiga was so slow.  As I recall, it was because Paula (which handles the floppy disk IO) is incapable of dealing with the data at full speed.

Well, actually data is transferred at the same speed, not half. The disk rotates at half speed. It's the Amiga floppy DMA channel which cannot operate at different speeds. It always writes data at the same speed. So if you want twice as much data on the same disk space, you have to rotate the disk at half speed. If you want to rotate the disk at the same speed, you have to double the DMA rate which is impossible on the Amiga's architecture.

Bye,
Thomas
 

[Thomas]

suggesting that you would not notice any slow down

Well, there is twice as much data for each track, so each read and write operation needs twice as long. Although the same amount of data is transferred in the same time, you feel as if it is slower because you usually measure floppy speed by the track clicks. And certainly you need twice as long to format 1760KB than to do it with only 880KB.

Bye,
Thomas