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You CANNOT add slower modules to a system designed for faster modules. For example, you cannot add 66MHz modules to a system designed for PC133.
You should NOT use a PC133 or PC100 with a 66MHz front side bus system. You should only use 66MHz memory modules with a 66MHz front side bus system.
You CAN use PC133 modules with a 100MHz front side bus system and vice versa. However, keep in mind that your memory will only be as fast as the slowest "link" in the system. If you install PC133 modules with a 100MHz front side bus or PC100 modules with a 133MHz front side bus, your memory will only run at 100MHz
If you have recently installed memory, again, check it is tightly in place.
If all memory is seated properly,and you're still getting the error, enter the computer CMOS and ensure that the CMOS memory settings are properly set for the amount of memory you have in the computer. Failing this, it is possible you might have some bad memory.
Once data starts flowing, there is no effect. Bear in mind, a clock cycle for a PC100 module is 10 nanoseconds so you probably won't notice a significant performance difference.
Most systems will accept either latency part. However, there are some systems that require either CL2 or CL3 parts.
Mac IIfx uses 64 Pin SIMM modules.
Mac Plus, Mac SE, Mac Classics, Classic II, Color Classic, Mac LC, LCIII, Performa 200,400, 405, 410, and 430 utilize 30 Pin SIMMs.
New Quadras, newer Performas, and Centris series utilize 72 Pin SIMMs.
Most MacIntosh computers come with onboard permanent memory and can utilize 72 Pin SIMMs 1 at a time.
Mac Performa 6400/180 & 200 models require 168 Pin DIMMs to upgrade.
Memory Type: Fast Page Mode DRAM
The pins on a DIMM are not connected, providing two lines of communication paths between the module and the system, one in the front and one in the back.
SIMMs and DIMMs are not interchangeable; they are different sizes and they install into different types of sockets.
The most important thing to know is that you cannot use RDRAM in a system designed for SDRAM or vice versa. The two types of modules are different sizes and shapes, so they won't even fit into the same memory slots. You should buy whichever memory type was designed for your system.
Which type is right for you?
As a general rule, it is best to match the type of memory that is currently in your system. However, it is possible to mix and match RDRAM speeds under certain conditions.
You CANNOT add slower modules to a system designed for faster modules. For example, you cannot add PC600 modules to a system designed for PC800.
You CAN add faster modules to a slower system, but there is no real benefit to doing so. For example, you can add PC800 modules to a system that was designed for PC600 modules, but your memory will not get any faster as a result. If you want your system to be faster, you should add more megabytes of memory.
Registered and unbuffered modules cannot be mixed in the same system.
If you do not see an option for ECC memory when searching for your memory upgrade, your system most likely has non-ECC memory installed and will not support ECC memory. In this case, you should upgrade your system with non-ECC memory (standard).
If your system has ECC memory, you should choose the upgrade option with "w/ECC". If you determine that your system is using non-ECC (standard) memory, you should select the upgrade without ECC in the description.
There is a slight decrease in performance, but it's usually approximately 3-4% on PC133 CAS2 ECC SDRAM insignificant since 3% is barely within the margin of error on benchmarks
ECC more expensive than Non-ECC, but not all motherboards support ECC ram. check with your Motherboard manufacturer before purchasing Ecc Memory. It's often used in high end systems, or servers.
You can tell which kind you have by looking at one of the modules currently in your system. Count the number of black chips on one module. If the number of chips can be evenly divided by three or five, you should buy ECC or parity (whichever is offered for your system). If not, you should buy non-parity.
For example, if one of your modules has nine chips, you should buy ECC or parity. If one of your modules has eight chips, you should buy non-parity.
Without some specific tweaks, this is true!
To tweak your system to handle more than 512mb of RAM (only if you're using Windows 98/98SE !),
see this Microsoft Knowledgebase article
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