16 megs or 28 megs

16 megs or 28 megs

Post by Daniel Prin » Wed, 19 Jun 1996 04:00:00



I have a system with an AMD 486DX4/100 and 256K of direct-mapped
write-back cache and 12 megs of 70 ns ram.  This system has an
AMI BIOS Dated 07/25/94 and a SIS chipset.  I can easily expand
this motherboard to either 16 megs or 28 megs by adding one 72
pin single sided SIMM.

I have read that if systems with direct mapped caches are
expanded to more than 16 megs of ram they get much slower
because every time the processor changes which 16 meg it
addresses the cache becomes invalid.  Is this true?

Is there any way I can prevent this other than disabling the
external cache entirely or replacing the motherboard?  Would
increasing the total amount of cache ram to 512K or one meg help?
This BIOS allows the user to set two areas of memory as non-
cacheable but they seem to be limited to four megs each.  Would
it help to make eight of the 28 megs non-cacheable?

With my motherboard, would it be better for me to upgrade to 16
megs or 28 megs for running OS/2 or Windows 95?  Thank you in
advance for all replies.

If there is another newsgroup that would be more appropriate for this
question, please let me know.

If it is not too much trouble, please send e-mail as well as
answering in the newsgroup.  My news feed is not always that
reliable (I see replies to messages I never see every day) and I
am sometimes too ill to check my newsgroups for several days.  
Thank you in advance for all replies.

 
 
 

16 megs or 28 megs

Post by steve am » Fri, 21 Jun 1996 04:00:00



Quote:e) writes:

:>
:>I have a system with an AMD 486DX4/100 and 256K of direct-mapped
:>write-back cache and 12 megs of 70 ns ram.  This system has an
:>AMI BIOS Dated 07/25/94 and a SIS chipset.  I can easily expand
:>this motherboard to either 16 megs or 28 megs by adding one 72
:>pin single sided SIMM.
:>
:>I have read that if systems with direct mapped caches are
:>expanded to more than 16 megs of ram they get much slower
:>because every time the processor changes which 16 meg it
:>addresses the cache becomes invalid.  Is this true?
:>
:>Is there any way I can prevent this other than disabling the
:>external cache entirely or replacing the motherboard?  Would
:>increasing the total amount of cache ram to 512K or one meg help?
:>This BIOS allows the user to set two areas of memory as non-
:>cacheable but they seem to be limited to four megs each.  Would
:>it help to make eight of the 28 megs non-cacheable?
:>
:>With my motherboard, would it be better for me to upgrade to 16
:>megs or 28 megs for running OS/2 or Windows 95?  Thank you in
:>advance for all replies.
:>
:>If there is another newsgroup that would be more appropriate for this
:>question, please let me know.
:>
:>If it is not too much trouble, please send e-mail as well as
:>answering in the newsgroup.  My news feed is not always that
:>reliable (I see replies to messages I never see every day) and I
:>am sometimes too ill to check my newsgroups for several days.  
:>Thank you in advance for all replies.
:>
:>

I'm not expert, so don't expect prose.  The thing about 256K addresing 16
megs sounds familiar.  However, I'm not so sure that's it's a big drawback,
considering the advantages you'll gain with 28 megs: such as larger DISKCASHE
setting, less swapping etc.  My machine isn't a powerhouse, a 486DX4-100, but
with 32 megs it's really nice.  And my work machine, which is a 486DX-33, was
upgraded from 8 to 24 megs last week and you wouldn't believe the
difference.  The simple truth is, Warp loves RAM.  Feed it lots.

Steve Ames


 
 
 

1. Adaptec 1542CF (16 meg vs 8 meg) problem fixed

A month or so ago I posted that I had installed an Adaptec 1542CF with disk,
and upgraded from 8 meg to 16 meg, and that OS/2 halted whenever I accessed
the SCSI.  Removing the new memory solved it, but why wasn't clear.  I
took it to a shop which told me that OS/2 was designed for IBM machines and
was not compatible with my 16 meg or SCSI adapter.  Since I was also having
video problems outside OS/2 (which the shop knew) I took it to another shop
for the video problems, mentioned the SCSI problems under OS/2, and they said
I probably had bad video drivers and that I should get new drivers and
reinstall Windows.

Anyway, the problem was solved quite by accident.  My officemate was helping
me carry the PC back and happened to notice in the manual for the video card
that there was a "memory aperture", the location of which apparently varies
according to the amount of memory in the system.  Disabling this solved all
my problems.  

The amount of misinformation I got doing this was phenomenal.  Professional
repair/installation people, besides the stuff above, also told me I couldn't
have a SCSI disk in the same box as an IDE and told me that I should have a
driver for my monitor as well as for my video card.  It's all very
disheartening.  But I'd like to thank everyone who sent mail and tried to
help me find a solution.  I can now run OS/2 just fine.

Thanks much.
--

-- Alan                        # Mountain Dew and doughnuts...

                               # of the day.

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13. 16 Megs -> 32 Megs...Performance Improvement?