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From: clemc@ccc.com (Clem Cole)
Subject: [TUHS] 2.9BSD on an actual rl02 - swap confusion
Date: Sun, 8 Feb 2015 17:03:17 -0500	[thread overview]
Message-ID: <CAC20D2Mqf-c=DFMqRNZwxAEucZVpfwnTNJq8eo+ACWOm-NhRMQ@mail.gmail.com> (raw)
In-Reply-To: <20150208204207.7860218C0BE@mercury.lcs.mit.edu>

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On Sun, Feb 8, 2015 at 3:42 PM, Noel Chiappa <jnc at mercury.lcs.mit.edu>
wrote:

> I don't know how the later systems work, but in V6, the swap device, and
> the
> start block / # of blocks are specified in the c.c configuration file (i.e.
> they are compiled into the system). So you can take one partition, and by
> specifying less than the full size to 'mkfs', you can use the end of the
> partition for swap space (which is presumably what's happening with
> /dev/rl0
> here).
>
​Ah Noel - Thanks for the refresher course.   That's right.  I now remember
it.  I knew it was compiled into the kernel but I had forgotten the details.

It was not until much later that the swap image became less screwed
down/more reflexible.   You first needed to get to larger disks (rp05/rp06)
which had to be partitioned because they overflowed a 16 bit integer​.
Once people started to partition them, then all sort of new things occurred
and I that's when the idea of a dedicated swap partition came up.   I've
forgotten if that was a BSDism or UNIX/TS.   Certainly by the time of Sam's
4.1A?? configuration tool that created conf.c and low.s it had already been
in for a while.

As I recall in V6 and I think V7, the process was first placed in the swap
image before the exec (or at least space reserved for it).   So you had to
have a swap space to boot because to fork the "init" it needed to assigned
to the swap space (chick/egg issue). When demand support was added to the
kernel, the process did not have to have that requirement, so it meant swap
set up could be a post initial program load operation for the start
sequence.

Clem


Clem
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  parent reply	other threads:[~2015-02-08 22:03 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-08 20:42 Noel Chiappa
2015-02-08 20:52 ` Jacob Ritorto
2015-02-08 22:03 ` Clem Cole [this message]
2015-02-08 22:09   ` Ronald Natalie
  -- strict thread matches above, loose matches on Subject: below --
2015-02-08 22:42 Noel Chiappa
2015-02-08 23:45 ` Clem Cole
2015-02-08 19:28 Jacob Ritorto

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