FAQ - Frequently Asked Questions
The following is a list of answers to frequently asked customer questions. Maybe you can find the solution to that troublesome brain-twister here. If not, contact our technical support department.
What is a SIMM, what is a DIMM, and what is the difference?
What is virtual memory?
Why should I buy real RAM when I can use Virtual memory?
What is interleaving?
What kind of memory do I need for my Mac?
Should I use a SIMM / DIMM tree?
I just put a single SIMM in my Power Mac 6100/7100/8100 or Pentium or only 2 modules in my Macintosh II ci and now it will not boot up.
I just installed memory into my Macintosh and now it looks like the system is using it all.
I just installed a memory module into my computer. Now when I start up the computer, my computer plays a song, or will not start up at all. If I take the module out again, everything works perfectly.
I just installed a DIMM into my Macintosh and it does not show up when I look under "About This Macintosh."
I just installed memory into my PC and get a memory mismatch error on startup.
Is there any benefit to using memory that is faster than what my computer is designed for?
What is EDO Memory?
What does the term DRAM mean?
What is SDRAM?
What is the difference between buffered and unbuffered DIMMs?
Why is there a different type of cache for the 7500?
Gold vs. Tin lead contacts.
What is a SIMM, what is a DIMM, and what is the difference?
A SIMM is a Single Inline Memory Module. A DIMM is a Dual Inline Memory Module. Both modules have contacts along the bottom of the modules which fit into the socket of the computer. The difference is that on a SIMM both the front and the back of each individual contact are read by the computer as the same. On a DIMM the front and back of the contact are read as separate contacts. This increases the amount of contacts available in a given space. For example a SIMM with 72 contacts has 72 contacts. A DIMM with 72 contacts in reality has 144 contacts.
What is virtual memory?
Virtual memory is the use of part of your hard drive as RAM.
Why should I buy real RAM when I can use Virtual memory?
Virtual memory uses your hard drive as RAM. Access to RAM is in nanoseconds (fast), access to your hard drive is in milliseconds (slow). If you use virtual memory, it is like driving your car with the parking brake on. You can move, but not very fast. Virtual memory is good if you need to open an application or document you rarely use, and do not have enough real RAM to run it. Ideally, this is a temporary solution, in a rare or unique situation. If you have enough memory it is best to work in real RAM.
What is interleaving?
Memory Interleaving:
DIMMs have a 64bit wide data path. This means that they can only process data in 64bit blocks, which means that larger data blocks must be broken down in order to be addressed. Interleaving allows the system to see the two interleaved memory modules as one. This means that they now become a single 128bit data path. To create this wider data path the system writes to the same address in each module before moving on to the next address. The interleaved data path can handle larger blocks of data and this can contribute to faster system performance (5-10%) during memory intensive functions. Many of the newer PowerMacs and PowerPC Mac clones are capable of memory interleaving. SIMMs can also be interleaved in certain systems such as the Quadra 800. In its case the data path is increased from 32 to 64bits. Many Pentium based PCs also use a form of interleaving. Since most Intel based systems still use SIMMs, which have a 32bit data path, SIMMs are installed in pairs in order to create the 64bit data path necessary to be compatible with the 64bit Pentium processor. In all cases the modules to be used in interleaving must be identical.
What kind of memory do I need for my Mac?
Macintoshes use a variety of different memory modules; early Macs use 30 -pin modules, newer machines use 72-pin modules or DIMMs. Powerbooks take special modules. If you do not know what type of modules your machine requires, you may check our on-line configurator, or contact us at 800-688-7466.
Should I use a SIMM / DIMM tree?
This is a difficult question. The most likely answer would be no. Computers by their nature are looking for an excuse to fail. Using a DIMM (or SIMM) tree is making a machine do something that the designers did not specify, thereby increasing your chance of failure. These trees are good however if you have a substantial investment in memory for a machine and decide to upgrade your machine to a newer model
I just put a single SIMM in my Power Mac 6100/7100/8100 or Pentium or only 2 modules in my Macintosh II ci and now it will not boot up. Why?
Memory modules supply your machine with a highway or bitpath for data. A 72-pin module will allow a 32 bit path for data, while a 30-pin module will supply you with an 8bit path and a DIMM will supply you with a 64 bit path. Sometimes, computer technology overtakes memory technology. For example a computer might come out which requires a 64 bit path when only 32 bit memory is available. These machines make up for this problem by using multiples of the smaller bit path modules to make up a pair or bank. For example you can use two 72 pin (32 bit modules ) to make up a 64 bit path bank. Where this becomes a problem is when you try to put only 1 module in or try to mix different densities within a bank (i.e. 1- 4MB module and 1-8MB module). When you do this, you do not complete the bank correctly and the machine will not boot properly.
I just installed memory into my Macintosh and now it looks like the system is using it all.
This is the number one frequently asked question. The problem is that you need to turn on 32-bit addressing in your memory control panel (under apple menu, select Control Panels, then select the Memory control panel, and turn on 32 bit addressing) and then reboot the machine. Now when you go to "About this Macintosh" under the Apple menu, things should be back to normal. Without 32 bit addressing, your Mac can only access 8MB of memory. When you install more than 8MB, your Mac recognizes the additional memory, but can't do anything with it, so it appears that the additional memory is being used by your system.
The exception to this rule is for machines that do not have 32 bit clean ROM such as the Mac II, the Mac IIix, and the Mac IIcx. These require a patch called Mode 32 in order for the machine to be able to recognize the additional memory. In addition to the patch, the Mac II and IIix require additional hardware and or a special memory module to access more than 8MB of memory.
I just installed a memory module into my computer. Now when I start up the computer, my computer plays a song, or will not start up at all. If I take the module out again, everything works perfectly.
The first step is to make sure the module is installed correctly. Remove the module and carefully replace it in the socket on a SIMM. Make sure that it is level in the socket before you tilt it into position. Once it is in position, make sure that each of the retaining clips are secure around the sides of the modules. If you have problems, do not force the module, simply return the module to its starting position and try again. Make sure these clips are locked around the edge of the SIMM. The SIMM should feel secure in the socket. If you are still having problems with the module and your machine allows, try it in another socket (preferably a known working socket). If neither of these options help, you probably have a defective SIMM and need to contact TechWorks Technical Support for a replacement.
I just installed a DIMM into my Macintosh and it does not show up when I look under "About This Macintosh."
DIMM stands for Difficult to Install Memory Module (OK it really stands for Dual Inline Memory Module, but please humor me on this one). What is happening is that although it appears that the module is in the socket real good, it is really not making good enough contact to show up. There is a secret to installing DIMMs. First of all make sure that you place it correctly in the socket. It will only go one way; there are two notches on the DIMM which match up with the two notches in the socket. This keeps it from going in backwards. Next push down on the handle that is located on the DIMM Socket. You will then want to press the DIMM into the socket starting at the end furthest away from the socket handle. After this end is started and held down, press in the other side. The DIMM should then "zipper" and click into place, and the DIMM socket handle should pop up. Yes, it is a tight fit, but friction is the only thing that is holding this module in place and you do not want it falling out when you have to move the machine across the room.
I just installed memory into my PC and get a memory mismatch error on startup.
This is a normal error, and just means that the machine wants you to run its setup, so run the set-up, and save the changes, or write to CMOS. Restart the machine and everything should be fine.
Is there any benefit to using memory that is faster than what my computer is designed for?
No, using faster memory will not give you a performance boost. Memory modules just respond to requests from the processor. They do not initiate any action, it is a lot like a pitcher and a catcher in baseball. You may have the leagues fastest catcher, but he is limited as to how fast he can catch by how fast the pitcher throws him the ball.
What is EDO Memory?
EDO (Extended Data Output) DRAM :
All DRAM addresses data the way a spreadsheet does, by organizing data into rows and columns. When Fast-page Mode (FPM) DRAM accesses data it must find the row and column, and then read the data before moving on to find the row and column for the next piece of data. EDO RAM speeds this process up by allowing the steps to overlap. EDO RAM still must find the row and column of the data before it can read it, but now it can find the row and column for the next address, while it reads the data at the first address (and so on). This speeds up data transfer rates, since EDO RAM can access data continuously without waiting for addresses to be located. For a system to benefit from EDO RAM, it must be capable of addressing EDO RAM, and all memory installed must be EDO. Some systems will allow you to mix FPM and EDO RAM, but the EDO modules will perform as if they were FPM.
What does the term DRAM mean?
DRAM is an acronym which stands for Dynamic Random Access Memory.
What is SDRAM?
Synchronous DRAM (SDRAM):
The processes performed by the components in a computer are all coordinated by an internal clock. Traditionally DRAM has been considered asynchronous, because it has set its own fixed timers for reading and writing data. The time set for reading or writing data stays the same regardless of how long it actually takes to perform the task. So if the data that the DRAM is reading only takes half the time set aside, then it must wait until that cycle is over for it to move on to the next piece of data. Synchronous DRAM on the other hand does not have a fixed timer and synchronizes itself to the computer's own internal clock, so that SDRAM uses only the time required to read/write data, thus speeding data transfer rates by eliminating non-productive periods of waiting.
What is the difference between buffered and unbuffered DIMMs?
Buffered vs. Unbuffered DIMMs:
A buffer is like an interim storage tank for data between the RAM and system board. This buffer prevents data bottlenecks by providing a space for data to overflow into while it waits to be stored or processed. Buffered DIMMs have these buffers built onto the module. Since they can buffer themselves more, Buffered DIMMs can be handled by the system board. For example: the use of Buffered DIMMs is why PowerMac 9500s can handle up to 12-128MB DIMMs. On the other hand some systems have a memory buffer built onto the logic board and they use Unbuffered DIMMs. Using Unbuffered DIMMs and a single on-board buffer means that fewer modules can be handled by the system. Currently most Unbuffered DIMMs are in the SoDIMM family and are used in notebook computers, which do not have much RAM capacity to begin with (usually a notebook will only support two SoDIMMs) .
Why is there a different type of cache for the 7500?
The 7500 requires a special cache card because (to put it simply) normal cache cards cause too much noise on the processor bus. There are some versions of the 7500 motherboards which can use standard cache. If you are one of the lucky individuals who have one of these machines, and the cache works, be happy and do not just pull it out because everyone says it should not work. If you truly have a problem, the machine will freeze hard on startup, or freeze so frequently and hard that it will be quite unusable.
Gold vs. Tin lead contacts.
Basically, it's a chemistry thing. Any time you have two metals in contact and an electrical charge present, the potential for corrosion exists. Over the years module pin and connector metallurgy have changed back and forth from tin to gold several times depending upon the vendor, so it is fairly easy to wind up with mismatched metals.
The best rule of thumb is to do your best to make sure that the metal of the modules contacts is the same as that of the computer's socket. There are only two main choices: gold and tin lead (silver colored). You can tell the difference by the color. The good news is that this corrosion normally takes several years to show itself, and by the time it does the computer will probably be sitting in the garage holding a door open.