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From: marc@petrus.UUCP (Marc Pucci)
Newsgroups: net.followup
Subject: Unix physical block size
Message-ID: <701@petrus.UUCP>
Date: Sun, 24-Nov-85 22:17:00 EST
Article-I.D.: petrus.701
Posted: Sun Nov 24 22:17:00 1985
Date-Received: Mon, 25-Nov-85 07:46:10 EST
References: <298@weitek.UUCP> <228@polaris.UUCP> <942@wcom.UUCP>
Organization: Bell Communications Research, Inc
Lines: 17

> > it's partly a function of hardware as well.  tradition has it that all disk
> > blocks are 512 bytes.  this is fine on a smaller machine where there was
> > only 64K to work with, the CPU and memory are slow, and so was the disk.
> > you can make block sizes bigger, but still you have to live with hardware
> > that doesn't understand it.  
> 
> 	On System V, the physical block sizes are 1K.

I think the physical block-size is still assumed to be 512 bytes.  That is,
the assumed sector size of disks is 512.  When I did a port of system V to
a system with physical 1024 byte disk sectors, I had problems with programs
like ncheck, fsck, etc. with raw disk partitions.  They all assumed they
could seek to 512 (super-block offset) and read the superblock.  Unfortunatly,
the raw disk interface insists on only sector aligned, multiple-of-sector-size
reads.

Marc Pucci, Bell Communications Research, Morristown, NJ