systemdose
1 Copper

Optiplex 990 supported memory speed

I have a optiplex 990 and I wanted to verify the supported memory speeds.
all the documentation I have found only says DDR3, 1333MHz with up to 16GB with all 4 slots used.
but when looking for compatible memory upgrades crucial.com lists DDR3 at 1600MHz.
where can I find all the memory speeds that this machine supports?

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4 Replies
7 Plutonium

RE: Optiplex 990 supported memory speed

JEDEC DDR3  are  7-7-7-20 for DDR3-1066  (PC3 8500)   and 8-8-8-24 for DDR3-1333   (PC3 10,600)

Timing 9-9-9-24 DDR3 1600 (PC3 12800)  is backwards compatible to 1066 providing it matches the 7 - 7 - 7 -  20 timing.

The speed that it runs has nothing to do with the dell model and everything to do with the frontside bus of the CPU.  In newer models the memory hub is INSIDE the cpu.

In other words you don't get faster ram with a slow cpu.   Request denied.

 

 


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systemdose
1 Copper

RE: Optiplex 990 supported memory speed

I think there is a misunderstanding to what I am asking.

my question is what is the maximum memory speed that the Dell Optiplex 990 system will be able to use?

(i.e. DDR3  1600 -PC3 12800 ; DDR3-1866 -PC3-14900 ; etc)

all the documentation I have seen lists the Ram as:

16GB1 DDR3, 1333MHz, (4 DIMM)

8GB1 DDR3, 1333MHz, (2 DIMM)

ETC.

(no other speed info is given from all the documents I have looked at)

which is why I have this question.

(optiplex-990-customer-brochure.pdf)

I want to know all the possible memory speeds that the Optiplex 990 system will be able to use correctly with out causing systems issues.

down-clocking the memory speed is another question that I did not mean to imply.

now, since you mentioned down-clocking what is the maximum memory speed that the system is able to run at?

(so I am not paying extra for faster modules but not using that speed)

again I now have 2 questions:

1. all the possible memory speeds that the Dell Optiplex 990 system will be able to use without causing system errors?

2. maximum memory speed that the system is able to run at without causing system errors?

I hope this is now clear what I am asking.

thank you for your time

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7 Plutonium

RE: Optiplex 990 supported memory speed

Dell has not and will not validate speeds that did not exist at the time of  manufacture.  7 7 7 and 8 8 8 are not available in all timings all versions all speeds.  There is no one size fits all.  The ram in question is getting harder to find because its not manufactured for 5 years or more now.  The other issue is 1.35v or 1.5v is max for this chipset.

There are however 1.8v to 2.0v modules that would not be compatible.

The Optiplex  DOES NOT support BUFFERED, REGISTERED, ECC ram which has nothing to do with speed as they can have this at all speeds.

Standard name
 
Module name
 
Peak transfer rate
(MB/s)
Timings
(CL-tRCD-tRP)
CAS latency
(ns)
DDR3-800D
DDR3-800E
PC3-6400 6400 5-5-5
6-6-6
12.5
15
DDR3-1066E
DDR3-1066F
DDR3-1066G
PC3-8500 8533.33 6-6-6
7-7-7
8-8-8
11.25
13.125
15
DDR3-1333F
DDR3-1333G
DDR3-1333H
DDR3-1333J
PC3-10600 10666.67 7-7-7
8-8-8
9-9-9
10-10-10
10.5
12
13.5
15
DDR3-1600G
DDR3-1600H
DDR3-1600J
DDR3-1600K
PC3-12800 12800 8-8-8
9-9-9
10-10-10
11-11-11
10
11.25
12.5
13.75
DDR3-1866J
DDR3-1866K
DDR3-1866L
DDR3-1866M
PC3-14900 14933.33 10-10-10
11-11-11
12-12-12
13-13-13
10.56
11.786
12.857
13.929
DDR3-2133K
DDR3-2133L
DDR3-2133M
DDR3-2133N
PC3-17000 17066.67 11-11-11
12-12-12
13-13-13
14-14-14
10.313
11.25 
12.188
13.125 

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systemdose
1 Copper

RE: Optiplex 990 supported memory speed

I think there is still a misunderstanding, or I dont know enough details about RAM to fully understand your reply.

I did not meant to ask if dell will validate speeds that did not exist at the time of manufacture.

my question is related to what RAM speeds (in MHz) they designed the motherboard to utilize.

yes, I know that is FSB, but that is the only spec that I understand enough to be able to look for possible RAM modules to use in it. (without getting into more detail about RAM, such as timing and such)

the motherboard I was using before using this dell says it supportsRAM modules up to 800MHz speed  (but in some cases will use special 1066MHz modules).

the CPU FSB supported on that baord is up to 1333MHz.

(this is why I was asking about speeds of the RAM)

now the dell has a I5-2400 CPU which says Memory Types are 1066/1333MHz.

if the optiplex 990 only supports Sandy Bridge CPUs then mas FSB is 1333MHz.

(correct me if I am wrong here)

ok, so here are more questions:

if that is the case then the RAM that is used in this dell machine must meet the timings for the 1333MHz timings, no?

now, if that is all true and based on what you mentioned in previous post then I could potentially use any RAM speeds as long as it meets the timing of  7 7 7  or  8 8 8  ?

then that means max RAM speed (according to that table you gave) is DDR3 1600 that meet the 777 or 888 timing.

am I correct on any of the conclusions above?

thank you for your time!

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