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Applied Computer Technologies, Inc.
Advanced Technology Computer Systems, Peripherals, & Services
SIMMs (Single Inline Memory Modules) come in powers of 2, i.e., 1,2,4,8,16,32, etc. They are about 1 inch by 4-1/4 inches (72-pin) or 3-1/2 inches (30-pin) in size, and snap into simm sockets on the system board (also called motherboard, mainboard, or baseboard).
DIMM stands for Dual Inline Memory Module. Although it has only 84 leads, it reads both sides of the leads and technically is a 168-pin module. The DIMM is different from the SIMM physically in that there are two notches on the contact edge, and the module is slightly longer (5-1/4 inches instead of 4-1/4 inches). The DIMM module inserts into its socket straight down, without the need for tilting. DIMM sockets have release tabs at each end which act as levers to push the module up out of the socket during removal.
DIMMs have become more specialized in recent months. The first type of DIMM was a page-mode design, typically used in the PowerMac. The second generation is the synchronous DRAM (SDRAM), which is measured in clock speeds (8, 10 or 12), and not in nanoseconds (ns). The third type is the EDO DIMM. The EDO DIMM can be buffered or non-buffered, 3.3-volt or 5-volt, and may also be ECC (Error Code Correcting). As per your user manual, "x72" DIMMs are ECC, and "x64" are plain EDO. It is imperative to select the correct type of DIMM module when upgrading. In order for us to send you the proper type of DIMM, we need to know the make and model of your computer. This will insure accuracy in your order.
Specification: Common 30 pin simms are 1MB-1x8, 4MB-4x8 (nonparity) and 1MB-1x3, 1MB-1x9, 4MB-4x9 (parity); common types of 72-pin simms are 4MB-1x32, 8MB-2x32, 16MB-4x32 (nonparity) and 4MB-1x36, 8MB-2x36, 16MB-4x36 (parity). The "1x32", part is the simm specification, also referred to as 'architecture', because it indicates the simm design in terms of number of chips on the simm, and density of those chips. If you multiply the 2 numbers out, you get the total number of megabits and then divide by 8 (for nonparity simms) or 9 (for parity simms) to get the size in megabytes. They will also differ visually in having a notch in the middle of the connector edge.
Speed: Most SIMMs are 70ns, which is standard; 'ns' is nanoseconds, i.e. a 10^-9 second interval of time (one billionth of a second), and refers to how fast the memory operates. Faster memory costs a bit more, usually a $5 or $10 price difference between 60ns & 70ns, and 70ns & 80ns, but some older computers require slower memory, such as 100ns or 120ns.
Parity vs. Non-parity: Most Macintoshes use nonparity simms (x8, x32), and most PCs use parity simms (x9, x36). However, the recent trend is toward using non-parity simms on many Pentium boards (such as the Intel) because the chances of a memory error are so small, it might be years before the first error occurs. If there is an error with a non-parity simm, you won't know about it unless you spot it in your computer files, or output data, etc. When an error is detected in a parity simm, the computer grinds to a halt, losing whatever you are working on. Another type is ECC (error checking and correcting) used on high-end servers, and these will self-check and fix any errors.
How do I know whether or not my SIMMs are parity?
If the simms in your computer have chips in multiples of 3 (or 9), then those are parity simms, and you need parity simms. If the simms have chips in powers of 2 (2, 4, 8, ...) then it's non-parity.
What is a 'logic parity' or 'logic generator' SIMM?
Important: There is another type of simm known as 'logic parity', and these are often advertised and sold as 'parity', but they are not 'true parity'; they trick the system board into thinking they are parity simms, without doing any error checking. They're inferior and incompatible with many system boards (especially name-brand units), and are sold as cheaper parity simms. Other inexpensive simms (off-brand makes) are turning up on the market, and many of these are not up to spec. They may work okay on many common boards, but fail to work on the higher-quality, higher-performance boards, such as AST, HP, IBM, Digital, etc. To be safe, always request "Major Manufacturer" simms. We do not sell logic generators, nor certain other types of less reliable memory, and we do not deal in off-brand memory nor "remakes."
How do I know what type of memory module my computer takes?
1. You can find out specifics on your computer's current and possible memory configuration by referring to the documentation that came with it.
2. You may also email the make & model to Applied Computer Technologies, and we may be able to look up the details in a reference database, and determine the upgrade path options for your specific computer. We will also need to know the CPU type of the computer (e.g. '386, '486, etc.)
3. Or take off the cover and check the simm sockets visually.
What you need to buy will also depend first on whether you have any unoccupied simm sockets or if they are all filled, and second on whether your system board can take mixed simm sizes. If all simm sockets are occupied you may need to remove and replace at least some of the simms with higher density units.
For example, a Quadra 650 with 16MB system memory has 8 MB non-removable, and an 8 MB simm in one of the four simm sockets. To add memory, you can put in any combination of 4, 8, 16, or 32 MB simms in the three open sockets.
Other computers are less flexible, for example, the Performa 575 has 4MB nonremovable on the system board, and one simm socket which can take a 4, 8, 16, or 32 MB simm. If the simm socket is occupied, upgrading this machine requires the removal of the simm, and replacement with a higher density one.
To upgrade the typical PC 386 or 486 system board having two full banks of four 30-pin simms each: you remove one bank of simms and insert four higher-density simms. We don't sell the 2 MB 30-pin, so you would get four (4) of the 4MB-30pin. You are advised to get four (4) of the 4MB-30 pin, and avoid the discontinued 2 MB simms.
The amount of memory required is determined by the requirements of the application programs. The Windows '95 operating system needs a bare minimum of 8 MB RAM, and is noticeably better with 16 or 32 MB. Upgrading from 16 MB to 32MB on a Pentium will result in a very noticeable improvement in performance with any operating system.
Can I get trade-in credit for the smaller simms that need replacing?
We will buy consignment memory with a minimum of (2) 4 MB simms and will sell this memory as "used." Due to our generous warranties, the bulk of our sales is of new memory of only the highest quality available and the maximum compatibility. Our return rate for defective product is 1/4 of 1 percent (or 1 unit in 400), far lower than our industry average return rate of 1 in 50.
Why purchase memory from Applied Computer Technologies?
We have many types of memory expansion products, including proprietary upgrades for over 1300 types of motherboards, as well as SIMMs, SIPPs, DIMMs, DIPs, VRAM, cache and printer memory. We have been in the computer products business for 7 years and have extensive product knowledge, a large inventory, competitive prices, and efficient, friendly, reliable service.
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Changes last made on: April 1st, 1997