16M bound on ISA SCSI card??

16M bound on ISA SCSI card??

Post by Vi Chi Ch » Fri, 17 May 1996 04:00:00



hi there,

        I just get a used Adaptec 1540B and want to move my system to
        SCSI. however, just today I heard people in OS/2 community
        talking about this very card having problem because it can't address
        any memory above 16M, so OS/2 will use only < 16M for program, and
        all other above it as swap..
        I just want to know if this thing is true for Linux.. since I
        saw nothing of the sort mentioned in SCSI-HOWTO.
        Thanks a lot!

billy chan

 
 
 

16M bound on ISA SCSI card??

Post by Stephen Knila » Fri, 17 May 1996 04:00:00



Quote:>hi there,

>    I just get a used Adaptec 1540B and want to move my system to
>    SCSI. however, just today I heard people in OS/2 community
>    talking about this very card having problem because it can't address
>    any memory above 16M, so OS/2 will use only < 16M for program, and
>    all other above it as swap..
>    I just want to know if this thing is true for Linux.. since I
>    saw nothing of the sort mentioned in SCSI-HOWTO.
>    Thanks a lot!

>billy chan

Actually, this IS mentioned in the Linux docs.  It is NOT a problem with the
card, OR SCSI!  It is a problem with the ISA bus!  It has to do with the fact
that only 24 bits(address) are connected to the card.  If the program wants
DMA to access anything above 16MB, FORGET IT!  It is simply not possible due
to the fact that you need to use the A16-A31 lines.

SO, since it is a HARDWARE problem, Linux is ALSO susceptible.  It ALSO has
a config option to disable memory above 16MB!  AHHHH, so THAT is what that
stupid question is for!

Steve

 
 
 

16M bound on ISA SCSI card??

Post by Leonard N. Zubkof » Fri, 17 May 1996 04:00:00



  >hi there,
  >
  >  I just get a used Adaptec 1540B and want to move my system to
  >  SCSI. however, just today I heard people in OS/2 community
  >  talking about this very card having problem because it can't address
  >  any memory above 16M, so OS/2 will use only < 16M for program, and
  >  all other above it as swap..
  >  I just want to know if this thing is true for Linux.. since I
  >  saw nothing of the sort mentioned in SCSI-HOWTO.
  >  Thanks a lot!
  >
  >billy chan
  >

  Actually, this IS mentioned in the Linux docs.  It is NOT a problem with the
  card, OR SCSI!  It is a problem with the ISA bus!  It has to do with the fact
  that only 24 bits(address) are connected to the card.  If the program wants
  DMA to access anything above 16MB, FORGET IT!  It is simply not possible due
  to the fact that you need to use the A16-A31 lines.

  SO, since it is a HARDWARE problem, Linux is ALSO susceptible.  It ALSO has
  a config option to disable memory above 16MB!  AHHHH, so THAT is what that
  stupid question is for!

Yeah, but Linux also knows how to use bounce buffers where necessary to get
around this problem.

                Leonard

 
 
 

16M bound on ISA SCSI card??

Post by David Sega » Fri, 17 May 1996 04:00:00



Quote:>hi there,

>    I just get a used Adaptec 1540B and want to move my system to
>    SCSI. however, just today I heard people in OS/2 community
>    talking about this very card having problem because it can't address
>    any memory above 16M, so OS/2 will use only < 16M for program, and
>    all other above it as swap..
>    I just want to know if this thing is true for Linux.. since I
>    saw nothing of the sort mentioned in SCSI-HOWTO.
>    Thanks a lot!

>billy chan

As far as I know the 16M limit is a hardware limitation with all ISA
cards. Linux and Windows 3.11 are aware of this and copy the data via
an operating system buffer if necessary. I would be surprised if OS/2
did not provide a similar facility. It does not limit the memory used
by Linux and it is unlikely that a user would notice the decrease in
throughput caused by an aditional memory to memory copy.

Profectus Pty Ltd                 Compuserve: 100241,1211
25 Myrtle Road                    Telephone: +61 3 9830 5026
Canterbury, VIC, 3126 AUSTRALIA         Fax: +61 3 9830 0959
 
 
 

16M bound on ISA SCSI card??

Post by Or » Wed, 29 May 1996 04:00:00




Quote:>hi there,

>    I just get a used Adaptec 1540B and want to move my system to
>    SCSI. however, just today I heard people in OS/2 community
>    talking about this very card having problem because it can't address
>    any memory above 16M, so OS/2 will use only < 16M for program, and
>    all other above it as swap..
>    I just want to know if this thing is true for Linux.. since I
>    saw nothing of the sort mentioned in SCSI-HOWTO.

No.  Linux is designed sensibly and uses bounce-buffers to get DMAed
stuff into and out of >16mb on ISA machines.  It's a little slower,
of course, since the machine has to manually shove everything into
and out of that memory, but as far as the user and card are concerned
everything is working happily.

                 ____

                  \/

 
 
 

1. Using >16M on ISA bus

The title says it.  Can I use > 16M memory on a ISA bus running Linux?
I know there's DMA related limit to 16M on ISA bus, but I heard that
Linux solve that problem by not using memory >16M for DMA.  Can anyone
give me answer?

thanks

--

Rule # 1:  Network *is* computer

2. pascal for linux.

3. Solaris 2.4 X86 ISA >16M and Adaptec 1542B

4. Wonderful Website!!!

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