[Coco] KenTon - determining size of SCSI hard drive? (RGB-DOS HD-UTILS)

Allen Huffman alsplace at pobox.com
Mon Feb 6 12:35:39 EST 2017

On Feb 6, 2017, at 10:38 AM, Gene Heskett <gheskett at shentel.net> wrote:
> If talking about 256 byte sectors, and one bit in the fat per sector, 
> then that limit is in decimal bytes, 131,072,000 IIRC.  The maximum size 
> of the fat is 65536 bytes. At a cluster size of 1, it can represent 8x 
> that in sectors=524,288 sectors, times 256 to get bytes=134,217,728.

My math agrees with that. That's what I did for the CoCoSDC, so I am using the largest hard drive size without clustering.

For the EZ135, it may be a bit larger, so I may have to cluster just so I can keep writing and test the platters. But, if I can just query the drive, I will know if I even need to bother with that.

> When I added a second identical drive, I didn't limit format from doing 
> the whole drive, so that drive has a whole gigabyte, at a cluster size 
> of 16 available to os9. That means a file containing "hello coco" , less 
> than 1 sector long, occupies 16 sectors on the disk.  But that file 
> could have another 15 sectors worth of data appended to it without 
> taking up any more actual space.  And it just works. I wrote a dsave 
> based backup utility that I've run several times, but it takes a couple 
> days to run to make a full backup of the first drive to the 2nd. I'd 
> guess I may have by now, 100 megs of it used.

Back in the 90s, we were strongly advised not to make use of clustering because too many disk utilities were written to assume 1-sector clusters. They would destroy the disk. Because of this, I've never done it.

But, the largest hard drive I ever had hooked to my CoCo was the SyQuest 128MB drive, and that was perfect. I had a larger CompactFlash card with the Cloud-9 SuperIDE, but I split it between HDB-DOS and OS-9. That was still more than enough room.

> Not including the vdisks of course since I'm not much of an rsdos user, 
> I've never backed up quite a pile of 5.25" floppies to vdisks.

I imaged all my OS-9 disks as well, though I had some 80 track double sided disks I can't read since I no longer have that hardware. I also had to dig out my 720K floppy drive for a handful of those I had. Most of those 80 track drives were from my early OS-9 BBS days, pre-hard drive.

By doing a sector-by-sector copy, I cloned everything (including any deleted files) so I can peek around later if I want to.

I had some disks with bad sectors, and I'd make a second pass and try to do a file-by-file copy. I had many files I got "as much as I could get" that way.

>> I manually wrote out to 7FFFF sectors, I think, before errors, so I
>> guess that's it. It's a few sectors larger than what OS-9 can use, but
>> dEd was still able to get that far.
> Yup, you hit the end of the fat, Allen.

Will dEd not let me go beyond the FAT? I was hoping it was just sending driver sector seek commands, since I can go beyond the FAT if I format a 128MB image as, say, 40MB.

> Scsiquery could tell you its MUCH larger. Someone, Brian I think, told 
> you what to do to the makefile to get it included in the .dsk images. 
> That may make them bigger than a 35trkss image though.  Accessing 
> the .dsk thru drivewire, thats not a problem. I have one such file thats 
> 2/3rds full at 10 megabytes.  Sneakernet stuff I've downloaded with 
> linux, and I put it in that drivewire disk to make it instantly 
> available on my coco3.

I'm CoCoSDC, so it's all easy :) I mount my 128MB.DSK image and type "DOS" and it boots from that and uses it. It's even better than when I was using RGB-DOS + "LINK.BAS" to boot from an RS-DOS disk image in to the OS-9 partition.

Love the CoCoSDC.

		-- A

More information about the Coco mailing list