What does it mean: 256Kx4 DRAM?
Blake Patterson
I have 4 30-pin SIMMs (looking to add to an OLD machine) with two RAM
chips each on them (and one support chip of some sort). A quick web
search revealed that each chip is at:
256Kx4 DRAM
...how much RAM per SIMM?
Thanks.
bp
--
"Heisenberg may have slept here."
PCDoc
If that's a disappointment, contact me via e-mail, as I have several 30 pin
SIMMS in the 1 to 4 meg range that I have no use for.
"Blake Patterson" <bl...@blakespot.com> wrote in message
news:39E09909...@blakespot.com...
Scott Alfter
Hash: SHA1
In article <39E09909...@blakespot.com>,
Blake Patterson <bl...@blakespot.com> wrote:
> I have 4 30-pin SIMMs (looking to add to an OLD machine) with two RAM
>chips each on them (and one support chip of some sort). A quick web
>search revealed that each chip is at:
>
> 256Kx4 DRAM
>
> ...how much RAM per SIMM?
That "support chip" you mentioned is more than likely a 256Kx1 DRAM chip.
It and the two 256Kx4 chips mean you have a set of 256Kx9 (parity) SIMMs.
(I suppose it's also possible that the extra chip is some kind of fake
parity chip that sees what's being accessed and generates the appropriate
parity bit on-the-fly. I think I've heard of some companies doing this to
save the expense of an extra DRAM chip...did anyone ever really do this, or
is it just an "urban legend?")
_/_
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(IIGS( Scott Alfter (remove Voyager's hull number for email address)
\_^_/ http://salfter.dyndns.org
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Tim Mallery
>(I suppose it's also possible that the extra chip is some kind of fake
>parity chip that sees what's being accessed and generates the appropriate
>parity bit on-the-fly. I think I've heard of some companies doing this to
>save the expense of an extra DRAM chip...did anyone ever really do this, or
>is it just an "urban legend?")
Very real and very common around 8 years ago or so.
Just Bud
> I have 4 30-pin SIMMs (looking to add to an OLD machine) with two RAM
>chips each on them (and one support chip of some sort). A quick web
>search revealed that each chip is at:
>
> 256Kx4 DRAM
>
> ...how much RAM per SIMM?
256K.
To reply by email, remove the XYZ.
Lumber Cartel (tinlc) #2063. Spam this account at your own risk.
Just Bud
>You have a total of 1 Meg of RAM. Each SIMM is 256K.
Uh, 256K bits x 8 bits is 256KBytes.
Blake Patterson
> That "support chip" you mentioned is more than likely a 256Kx1 DRAM chip.
> It and the two 256Kx4 chips mean you have a set of 256Kx9 (parity) SIMMs.
>
> parity chip that sees what's being accessed and generates the appropriate
> parity bit on-the-fly. I think I've heard of some companies doing this to
> save the expense of an extra DRAM chip...did anyone ever really do this, or
> is it just an "urban legend?")
>
The "supporting chip", a web search reveals, is actually:
Fujitsu 256Kx3 F 81C256A-70 AAA2801j-06 (NMBS)
...interesting.
Blake Patterson
I know the mem board I want to add 1MB 30-pin SIMM's to (on an Amiga
2000) supports 8-bit SIMM's. I see lots of parity 9-bit SIMM's around
on eBay. Would these likely work in a board that supports non-parity?
I am not sure if it will take parity.
Thanks.
Mark Valiukas
> >save the expense of an extra DRAM chip...did anyone ever really do this,
or
> >is it just an "urban legend?")
>
There were two big problems with this approach.
1) Timing issues. The parity calculation takes time - so, you have to
hope that the "parity bit generator" is able to perform the calculation
between when the memory address is requested and when the machine expects
the address to be readable. This didn't always happen, and caused
intermittent problems on some boards.
2) Quality. If the memory manufacturer was prepared to fraudulently sell
parity-generator modules as full parity, then they were also unlikely to
care about things like proper quality control or quality components.
There were, however, a few cases in which they were useful. Some 386 and 486
motherboards I've seen will only accept parity RAM. I believe this was
probably the original motivation behind the invention of the parity
generator chip - to offer a cheaper alternative in this situation.
Mark.
hweidner
(I should pay for postage; or more specifically, get a local charity to
pay the postage!)
I have set up some donated 386s in a charity sponsored "Mothers day out"
program for preschoolers. (I don't work there, I just got volunteered
to run the computer center.)
I have found a few commercial DOS programs for pre-readers, but licenses
are expensive. There is some decent Win 3.1 shareware/freeware for
pre-readers; so if I could bump up the 386s to at least 2 meg of RAM
(some have 640k, some have 1 meg) I could give the kids more variety of
games to play with.
Helen Weidner
PCDoc wrote:
>
> You have a total of 1 Meg of RAM. Each SIMM is 256K.
> If that's a disappointment, contact me via e-mail, as I have several 30 pin
> SIMMS in the 1 to 4 meg range that I have no use for.
>
> "Blake Patterson" <bl...@blakespot.com> wrote in message
> news:39E09909...@blakespot.com...
> >
> > I have 4 30-pin SIMMs (looking to add to an OLD machine) with two RAM
> > chips each on them (and one support chip of some sort). A quick web
> > search revealed that each chip is at:
> >
> > 256Kx4 DRAM
> >
> > ...how much RAM per SIMM?
> >
David T. Wang
: I could use some donated old memory sticks.
: (I should pay for postage; or more specifically, get a local charity to
: pay the postage!)
: I have set up some donated 386s in a charity sponsored "Mothers day out"
: program for preschoolers. (I don't work there, I just got volunteered
: to run the computer center.)
: I have found a few commercial DOS programs for pre-readers, but licenses
: are expensive. There is some decent Win 3.1 shareware/freeware for
: pre-readers; so if I could bump up the 386s to at least 2 meg of RAM
: (some have 640k, some have 1 meg) I could give the kids more variety of
: games to play with.
Do these 386's take 30 pin simms?
Some of the earliest 386's take DIP's, and 1 Mbit DIP's are both hard to
find and rather expensive now, while 30 pin simms are plentiful and
rather in expensive. I think I can scrape up a small boatload of them.
-
compress 2:1 for email address.
ddaavveewwaanngg@@wwaamm..uummdd..eedduu
Quadrajet1
>> news:39E09909...@blakespot.com...
>> >
>> > I have 4 30-pin SIMMs (looking to add to an OLD machine) with two RAM
>> > chips each on them (and one support chip of some sort). A quick web
>> > search revealed that each chip is at:
>> >
>> > 256Kx4 DRAM
>> >
>> > ...how much RAM per SIMM?
>> >
>> > Thanks.
A Mac uses 8 bit memory, the PC uses 9 bit (typically). The Mac SIMM uses
either (8) 256K x 1 chips, or (2) 256K x 4 chips. Add them up and you get 256K
x 8 total. Same goes for the 1M x 4 and 4M x 4 chips. The PC SIMMs use (2)
256k by 4 chips, and (1) 256k x 1 chip for a total of 256k x 9 on a SIMM.
A Mac 512K SIMM has (4) 256k x 4 chips, and a special PAL chip to tell the
Mac what to do with that wierd configuration.
Raymond