[Coco] question about file transfers from PC

[Gene Heskett]

On Sunday 02 August 2009, Stephen Adolph wrote:
>I guess I am understanding why OS-9 seems like the right answer for a
>lot of users...no limitations I assume on the structure of the hard
>drive?
>
There are some restrictions, most caused by the 64k limit to the size of the 
file allocation table which starts at LSN1 of the drive.  Because it runs out 
of bits to represent each individual sector at about 131 megabytes, for larger 
drives it is required to change the size of the cluster that a bit represents, 
to 2, 4, etc in powers of 2 increments.  Each such increment doubles the size 
of the drive that can be handled.  The tradeoff is that the minimum allocation 
also grows.  To 2 sectors, then 4, 8 etc.

I haven't personally found this to be a problem in actual usage.  My drive is 
a 1GB seagate on a tc^3 interface.

Where there has been a problem, it is more generally going to be related to 
the 'SAS' value in the descriptor, and small values such as the default of 8, 
can and have been used up because the FD.SEG section of a files descriptor 
sector only has room for 48 entries.

I have made some noise in past years that this SAS value should be defaulted 
to at least 20 (it is a hex value, so that is 32 actual) in order to conserve 
this resource, and to speed up floppy writes too as that reduces the number of 
re-seeks that must be done in order to allocate the space to write the file 
to.  If doing really big files, I have been known to temporarily set SAS to 
FF.  This does no harm as the allocation will be reduced to the actual size of 
the file when the file is closed, and the next allocation request will start 
with the next available cluster that is SAS size in contiguous space.

>Regardless, for now I just want to use the standard system I/O wise.
>thanks for the info.
>
>Steve
>
>On Sun, Aug 2, 2009 at 8:29 PM, Darren A<mechacoco at gmail.com> wrote:
>> On 8/2/09, Stephen Adolph wrote:
>>> I don't quite understand why a disk file .DSK can't be loaded into any
>>> virtual disk slot.
>>>
>>> What I'm used to with the 2 emulators, is that you can load a .DSK
>>> file into any of the emulated floppies.
>>
>> --
>>
>> The four slots in the DriveWire server do not correspond to the four
>> floppy drives supported by standard Disk Basic.  Each slot represents
>> a virtual hard drive which has the capacity to hold 256 virtual floppy
>> disks.  Only one of the virtual hard drives is active at a time.  You
>> use the DRIVE #n command (the # is required) to specify which virtual
>> hard drive (server slot) is active.
>>
>> For example If you mount a typical 35 track DSK file in slot 3 of the
>> server, you cannot access it using a command like DIR 3.  You must
>> enter DRIVE #3 to tell the system that server slot 3 is the current
>> virtual hard drive, then DIR 0 will access the first (or only) virtual
>> floppy disk in that file.
>>
>> Darren
>>
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> http://five.pairlist.net/mailman/listinfo/coco
>
>--
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>Coco at maltedmedia.com
>http://five.pairlist.net/mailman/listinfo/coco


-- 
Cheers, Gene
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