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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.unix.wizards
Subject: Re: BSD 4.2 minphys() < 64K
Message-ID: <7423@utzoo.UUCP>
Date: Tue, 16-Dec-86 17:41:53 EST
Article-I.D.: utzoo.7423
Posted: Tue Dec 16 17:41:53 1986
Date-Received: Tue, 16-Dec-86 17:41:53 EST
References: <376@wyszecki.munsell.UUCP>
Organization: U of Toronto Zoology
Lines: 17

> Why does minphys() in BSD 4.2 systems still limit block i/o transfers to
> 63 * 1024 bytes?  I assume that this is an ancient artifact from PDP-11
> days...

Provided the disk controller and the bus being used can cope, I can't see
any good reason to retain the restriction.  Bear in mind that most Unibus
controllers tend to use 16-bit transfer-size counts, and any Unibus I/O
is limited by the 256KB Unibus hardware address space.  For non-Unibus
controllers, I can't see any good reason for the limitation unless there
is some other stupid problem with the VAX hardware (I don't have a VAX
and don't want one).

This doesn't mean that there isn't something silly in Berklix that will
break if you remove the limit...
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,decvax,pyramid}!utzoo!henry