Selecting Memory
It's pretty well accepted now that, in addition to defragmenting yoursystem, adding more memory (RAM) is one of the best ways to boost the performance of your computer. Having runWindows NT on systems with 16, 32, 64, 96 and 128 megabytes of RAM, we can assure you that you cannot have toomuch memory; the system just gets faster and faster. We consider 64 megabytes to be the minimum amount to use forWindows NT. However, there appears to be a fair amount of confusion about what kind of RAM to get.
RAM Types
First, RAM comes on a small card, or "stick"; the 72-pinSIMM (Single In-Line Memory Module) and the longer 168-pin DIMM (Double In-Line Memory Module). So far, SIMMs arecheaper per megabyte than DIMMs. While some older motherboards only have slots for the shorter SIMMs and some boardsonly accept DIMMs, most boards will accept both. The usual arrangement is to have two, four or eight "banks",with two SIMM slots and one DIMM slot for each bank. You cannot use both SIMMs and DIMMs in a given bank, but youcan use, say, the SIMMs in Bank 0 and the DIMMs in Bank 1. Most, or perhaps all, Pentium motherboards require thatSIMM sticks be installed in pairs.
The next thing to check is the access time. Most RAM has a 60-nanosecond(ns) access time, but 70 ns is still common. A motherboard that supports 70 ns RAM will also work with 60 ns RAM,but if your motherboard manual specifies 60 ns or faster, it will burn out a 70 ns stick.
Does Parity Matter?
Parity is short for "parity checking". This is a data checkingprocedure in which a ninth bit is used for each byte of RAM, which is set to 0 or 1 depending on the sum of theeight bits in the byte. That is, you count the number of ones in the byte and (when using "even" parity)if the result is even, the parity bit is 0, while if the sum is odd, the parity bit is 1. The parity bit valueis saved when data is stored in the memory, and checked when the data is read, to ensure that the data read isnot corrupt.
RAM chips have become much more reliable, so parity checking is nowgenerally unnecessary, but if memory errors can be expensive for you, consider RAM with parity. We have never seena DIMM stick with paritywe don't think they are available. That's a pretty good indicator that parity checkingis no longer needed.
The sticks have an identifying description such as "8x36-60ns"or "4x32-60ns". If the number after the "x" is divisible by 9, the RAM uses parity; ifit's divisible by 8, it does not use parity.
Check the Pins!
The type of metal used in the pins and the slot is often ignored.Some use gold, others use tin. Do not mix the two. When you put two dissimilar metals in contact and apply heat,they can generate small amounts of electricity. This can be enough to interfere with the signals between the RAMand the CPU, changing a bit in the data being transmitted.
The dissimilar metals can also corrode each other, eventually insulatingthe pin from the slot, and stopping all signals. Even a little corrosion can interfere with data transfer. Beforeinstalling RAM (or any card, for that matter), it's a good idea to clean the contacts. A pencil eraser does anexcellent job on the pins, but is too big to fit in the slot. You can insert and remove a card four or five timesto polish corrosion out of the slot, then clean out the slot with a stiff brush and a blower. Then polish the pins,brush them off and install the card. If you are getting strange intermittent problems with a card or with RAM,cleaning the contacts may solve them. Remember to ground your body before touching any card.
Warranty
RAM sticks come with warranties from 30 days to lifetime. In general,the longer the warranty, the higher the price. If a memory failure would be expensive, you should get RAM witha lifetime warranty, but for most systems, it's probably not worth the extra cost. For our home systems, we havenever bought RAM with more than a 90-day warranty and in about 20 sticks we have never had a RAM failure.
Before Buying
First, Read the Manual! Check your motherboard manual before buyingRAM. Find out what access time is needed, and what sizes of RAM can be used. Most motherboards have very specificrequirements for what combinations of memory sticks may be used, and where to install them. For example, it mayrequire that the largest sticks be in the first banks (starting with Bank 0) and the smaller sticks in the lastbanks. Make sure you buy a configuration that is compatible. The manual will also give you the minimum access speed;never buy slower RAM.
If you are not completely sure about the details, take the motherboardmanual to the store with you. You can also bring one of your existing sticks for comparison, but at least checkthe slot to see if it is gold or tin. Carry the stick in an anti-static bag and treat it gently. Also letthe folks at the store know you have it when you come in!
Many sales clerks are not very knowledgeable about technical detailsand some will fake it. If you have the manual and a sample stick, you can check details on the spot. Of course,you can always take the whole computer to a dealer and have them install the memory for you. They may charge you$30 or more, but if that's what you need, it's worth it.
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Executive Software Europe
