Re: [Bug-ddrescue] Using ddrescue on some really bad floppies

[Ian Oliver]

In article <address@hidden>, Charles Hemingway wrote:

> Are these disks perhaps formatted as HPFS?

Very unlikely. We were DOS only back then and the first cylinder contains a 
shrunk down DOS file system that contains just one file that spans the 
entire disk. Interestingly, this file is show as 1213440 bytes, which is 
79*512*30, which suggests that the tracks should have 15 sectors each and 
something else is going wrong. Might be time to try a different cable 
and/or motherboard.

> Non standard sector size sounds like something that video game companies 
> used to do back in the day to keep people from sharing their works.

We partly did it for that reason but also to pack more on a disk.

> Might it not be easier to obtain fastback and run it via DOSemu or 
> DOSbox?

I'm actually running Fastback (three different versions) under VirtualBox. 
This is because the floppies are so bad that they need lots of retries, far 
more than FB was prepared to use. I therefore used ddrescue to scrape every 
last sector off them before mounting the images as virtual floppies and 
unleashing FB. This worked on everything other than this one very early 
set.

> As for the bytes per sector, I vaguely remember reading in an early 
> ddrescue info:
> 
> (HD = hard drive, FD = floppy disk, CD = compact disc)
> 512 B for HD sectors (older HDs)
> 1024 B for FD sectors
> 2048 B for CD sectors
> 2352 B for raw CD sectors
> 4096 B for new HDs and SSD/USB flash memory devices.

I've been working from the table at the bottom of this page.

http://www.hpcc.ecs.soton.ac.uk/hpci/tools/floppy_disks.htm

All those floppies have 512 byte sectors but some double them up into 1k 
clusters to keep the fat smaller.

Regards

Ian