Anyone know how to add swap space?

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Aharon Robbins

Jan 25, 2021, 10:36:47 AM1/25/21
Does anyone know how to add swap space on a running system?


Aharon (Arnold) Robbins arnold AT skeeve DOT com

DoN. Nichols

Feb 7, 2021, 4:32:15 PM2/7/21
On 2021-01-25, Aharon Robbins <> wrote:
> Does anyone know how to add swap space on a running system?

IIRC, if you have a second disk you can partition it so part of
it can be added as swap space -- and then add it.

On OpenBSD and on Solaris 10 there are system calls under

No point to more than 4 MB of swap space, IIRC with the memory
management in the unix-pc/3b1/7300.

If you can't add another drive (e.g. if you haven't made the
modifications to *allow* a second drive) look into /usr/lib/iv and you
will find a lot of files defining the format of different disks. here
is an example:

#sccs "@(#)iv/lib:seagate225 1.1"
# Seagate 225
type HD
name sg225
cylinders 612
heads 4
sectors 17
steprate 0
badblocktable 1
loader /usr/lib/iv/s4load.silent

where, IIRC, the numbers after the "loader" entry are two '$' signs,
then three numbers. The first says that cylinder 0 is used for the boot
block, cylinder 4 starts the swap space, and cylinder 504 starts the
disk space for the OS and the users. It goes on from that to the max
number of cylinders above (612 in this case, so there is not much space
on this disk for the OS.

Anyway -- find the one in that directory which matches your
disk, (of course, back up *everything* first), make a copy of the boot
installation disk, and copy your file (let's say it was the seagate225
above) to a matching name but with the 504 edited to something bigger,
thus dedicating more space to the swap partition. (You really don't
have much room for this on the S225, so I *hope* you have something
bigger. If you have no modifications to the hardware to allow more
heads and cylinders, I think the best drive which will fit in the 7300
(without the hump under the monitor for a full-height drive) would be
the "Miniscribe 6085" which has the maximum cylinders (1024) without a
change of disk controller chip from WD-1010 to WD-2010, and a maximum of
8 heads.

You might want to go through the list of files in /usr/lib/iv,
and see which you can find available as a working disk which will work
in your system. If no mods to the system, maximum of 1024 cylinders,
and 8 heads. If swapped WD2010 chip in to replace the WD1010, you have
a maximum number of cylinders of 2048, but still are limited to 8 heads.
If you have put in the hardware mods documented elsewhere, you can
expand to 16 heads (the Maxtor 2190 actually has 1224 cylinders, and I
don't know of any which use the full 2048 cylinders.

Anyway -- edit the file as above, and put the edited and renamed
file into the boot floppy -- which formats and partitions the disk -- you
will lose everything already on the disk, of course, and when the
installation is complete, you will have more swap space -- and less
user space.

Of course, you do have to boot with that modified floppy,
remember to use the renamed and edited file when it asks for disk type,
and go through the full installation process.

> Thanks,
> Arnold

Good Luck,

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