🚀 go-pugleaf

In article <1421@cit-vax.Caltech.Edu>, mangler@cit-vax.Caltech.Edu (System Mangler) writes:
> 
> The object of sector searching is to avoid tying up the controller
> with disk rotational latency.  It only gains something if another
> drive is ready to do a transfer immediately.  This is an unlikely
> event on a low-end VAX, which doesn't have enough CPU power to
> keep a Massbus controller that busy, and which can ill afford the
> additional interrupts.
> 

Sector searching was introduced (as far as I know - there may have been 
prior art) by IBM with the 3330 DASD in about 1970, called Rotational
Position Sensing.  The idea was to optimize the use of S/370 channels,
rather than control units. It worked OK, but now has been enhanced to
allow the reconnecting controller to select among multiple attached channels,
thus improving the chances of a free channel being found when needed.
Since multiple controllers will normally be attached to a channel, the
controller is generally not as scarce a resource.

-- 
Mike Taylor                        ...!{ihnp4,hplabs,amd,sun}!amdahl!mat

[ This may not reflect my opinion, let alone anyone else's.  ]