Subject: Re: Source for SCSI driver info?
To: None <macbsd-general@NetBSD.ORG>
From: None <>
List: macbsd-general
Date: 05/03/1995 15:34:20
> At  8:42 AM 5/3/95 -0400, David C. Myers wrote:
> >Drew's driver seems pretty complete, with multiple message queues, real and
> >pseudo DMA, scatter/gather (whatever that means), and so on.
>              ^^^^^^^^^^^^^^

> Look at readv/writev.  A single IO call using a struct iovec argument will
> parcel out so many bytes to this location, so many to that, so many to the
> next, etc.  It's trivial to convert to a multiple read calls, but
> theoretically, potentially, more efficient, especially if you have smart IO
> subsystems like channels on IBM mainframes.
> ________________________________________
> Henry B. Hotz

Perhaps techniclly correct, but not very usefull in describing the concept
or why I might even care about it's existance. :)

Put simply, its a mechanism for reading/writing a large block of virtual 
memory to a device.  Keep in mind that virtual memory may look linear to 
your program but, in reality it is _scatter(ed)_ through out physical RAM. 
So you _scatter_ data into RAM say from the disk, and _gather_ it from RAM 
on it's way back out to the disk.