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COMPUTER BITS BY GREG SWAIN Adding RAM to your computer Do you run graphics-intensive CAD or Windowsbased software on your computer? If the hard disc indicator LED flick­ers constantly, give your system a shot in the arm by adding more RAM. Here’s how to do the job yourself. Although you can run Windows with 2Mb (two megabytes) of RAM (barely), 4Mb is better and 8Mb is a lot better. But even 8Mb of memory is insufficient with some applications. Photoshop, a popular picture editing program, requires a minimum of 10Mb to run properly, for example. Graphics, spreadsheets and drawing programs are particular­ly memory intensive, although they will generally keep working even when system RAM becomes low. This can happen if you are running several applications at once (multi-tasking) or if you are manipulating large spread­sheets or colour images. In this situation, the system frees up RAM by swapping its contents to a specially reserved area called the “swapfile” on your hard disc. In other words, the system treats an area of the hard disc as RAM so that, theoretically, you should have all the RAM you need for the job. There is a drawback to this scheme, however – hard disc access times are many orders of magnitude slower than RAM access times. A fast hard disc will have an average access time of about 10ms, whereas RAM is about 140,000 times faster with access times of 70ns or better. As a result, your system can slow to a snail’s pace when running some memory intensive applications. That’s because you have to wait as the system constantly shuffles data from RAM RAM modules (also known as SIMMs) come in various capacities. Shown here is a 30-pin 1Mb SIMM that carries nine individual memory chips (one for parity checking), although it’s also possible to buy 3-chip types of the same capacity. to the hard disc and back again as required. A sure sign that this is happening is almost continuous hard disc activity, as evidenced by a constantly flickering hard disc LED. Alternatively, you can get “out of memory” error messages when running some applications that require lots of RAM (although this can also occur for other reasons). If this is happening to your system, then it’s time to speed things up by adding more RAM. If you already have 4Mb, then you might like to consider going to 8Mb. If you already have 8Mb, then consider going to 12Mb or even 16Mb. Of course, if your pockets are deep enough, you can go much higher than this – up to the maximum allowable by your motherboard. On older 386 and 486 motherboards, this will generally either be 32Mb or 64Mb, while more recent machines can go as high as 128Mb. Doing it yourself At this stage, you are faced with a choice – you can either take the machine to a dealer and pay to have the memory upgraded or you can save money by doing the job yourself. It’s quite straightforward provided that you have basic mechanical skills and have retained all the documentation for your computer. The first thing to do is to refer to the manual for your system’s mother­ board. Inside, you will find a section on memory installation and there will be a table showing the possible memory configurations. Table 1 is a typical example for a 486 motherboard that supports up to 64Mb but note that your mother­board may differ markedly from this, so check the manual carefully. July 1995  63 TABLE : MEMORY INSTALLATION Bank 0 Bank 1 Bank 2 Bank 3 4 x 256KB Total 1MB 4 x 256KB 4 x 256KB 2MB 4 x 256KB 4 x 256KB 4 x 256KB 4 x 256KB 4 x 256KB 4 x 256KB 4 x 256KB 4 x 1MB 4 x 256KB 4 x 256KB 4 x 1MB 6MB 4 x 256KB 4 x 1MB 4 x 1MB 9MB 4 x 256KB 4 x 256KB 4 x 1MB 3MB 4 x 256KB 4MB 5MB 4 x 1MB 4 x 1MB 10MB 4MB 4 x 1MB 4 x 1MB 8MB 4 x 1MB 4 x 1MB 4 x 1MB 4 x 1MB 4 x 1MB 4 x 1MB 4 x 1MB 4 x 4MB 4 x 1MB 4 x 1MB 4 x 4MB 24MB 4 x 1MB 4 x 4MB 4 x 4MB 36MB 4 x 1MB 4 x 1MB 4 x 4MB 12MB 4 x 1MB 16MB 20MB 4 x 4MB 4 x 1MB 40MB 16MB 4 x 1MB 4 x 4MB 32MB 4 x 1MB 4 x 4MB 4 x 4MB 4 x 1MB 4 x 4MB 4 x 4MB 48MB 4 x 4MB 64MB Adding the extra memory involves pushing the module into its socket at an angle, then pressing it down so that it is held by the spring loaded clips at either end. A notch in one end of the module stops you from plugging them in the wrong way around. In this case, the mother­board has four banks of memory – banks 0, 1, 2 and 3 – and supports three different types of RAM modules or SIMMs (single in-line memory modules): 256Kb, 1Mb and 4Mb. In addition, each bank holds four SIMMs and you must fill each new bank completely with the same type of SIMM. Fig.1 shows the locations of these 64  Silicon Chip memory banks on this particular mother­board. An example will illustrate how this works. Let’s say that this particular motherboard has 4Mb of memory and that this memory consists of 4 x 1Mb SIMMs occupying bank 0. If we want to upgrade the memory to 8Mb, then it’s simply a matter of adding another 4 x 1Mb SIMMs to bank 1. From there, we can go to 12Mb by adding 4 x 1Mb SIMMs to bank 2 and finally to 16Mb by adding 4 x 1Mb SIMMs to bank 3. Note that to get the maximum 64Mb capacity, you would have to install 4 x 4Mb SIMMs in each bank. Another thing that’s obvious from Table 1 is that the SIMMs used in later banks cannot have a lower capacity than those used in earlier banks. This means that if 4Mb SIMMs are used in bank 1, for example, they must also be used in the re­maining two banks. It also means that existing SIMMs will have to be replaced with higher-capacity SIMMs in some cases, in order to achieve the desired total. Note also that some older 386 and 286 motherboards accept only DIL (dual-in-line) memory chips and do not support SIMMs. Once again, check the manual for your motherboard carefully. 72-pin RAM Generally speaking, most 486 (and earlier) machines accept 30-pin SIMMs. However, just to complicate matters, 72-pin SIMMs are also available. These range in size from 2Mb up to 64Mb and are used mainly in later 486 machines and in Pentium machines. As before, consult the manual to find out which type suits your particular motherboard. If this information isn’t listed, then you can easily discover which type your computer uses by removing its cover and inspecting the RAM sockets. If you have a motherboard with 32bit memory access, then it’s possible to expand the memory by plugging in one or more 72-pin SIMMs. The most commonly available sizes are 2Mb, 4Mb, 8Mb, 16Mb and 32Mb, although 64Mb SIMMs are also now becoming avail­able. On the other hand, motherboards with 64-bit memory access will require at least two extra SIMMs for memory expansion. Again, it’s simply a matter of checking the manual for the allow­ able memory configurations. Parity vs. non-parity Unless you know exactly what you are doing, you should always use RAM that includes parity (ie, 9-bit wide RAM). That’s because the original PC specification calls for parity checking and some motherboards can only work with this type of RAM. BANK 0 BANK 2 BANK 1 BANK 3 banks will be designated in screened printing, while for others you will have to check the location of each bank by refer­ring to the manual. The main thing to watch out for is that you plug the extra SIMMs into the next bank in the sequence. For example, if banks 0 and 1 are already occupied, the new SIMMs must be plugged into bank 2. As mentioned previously, a bank cannot be partially filled – it must either be empty or fully occupied. For 30-pin SIMMs, this means adding four extra modules (all the same type) to each new memory bank. To install each SIMM, you simply slide it into its socket at an angle as shown in one of the photos. The module is then pivoted in the socket so that it sits under the spring-loaded retaining clips at either end. Note that there is a polarising notch in one end of the SIMM, to prevent you from plugging it in the wrong way around. CMOS setup Fig.1: the memory bank locations on a typical motherboard. In this case, there are four memory banks & each bank carries four 30-pin SIMMs. Note that each new bank must be completely filled with the same type of memory. On the other hand, many mother­ boards have a facility for disabling parity checking, usually via the BIOS. In these cases, it’s often OK to use non-parity RAM and save a few dollars into the bargain. The proviso here, of course, is that you have to sacrifice the automatic error-checking that parity provides. Our advice is that you stick with the parity RAM when up­grading the memory on a PC, unless money is important to you and you know how to get into the CMOS setup and disable the parity checking (assuming that this can be done). That way, you will be on safe ground. RAM installation This is the easy part – all you have to do is remove the cover of the machine and plug the extra SIMMs into the next available memory bank(s). Before removing the cover screws, be sure to remove the mains plug from the wall to avoid any nasty shocks. Once the cover has been removed, a visual inspection will quickly reveal the location of the existing memory. On some motherboards, the memory When you switch your machine back on again, it will run through its RAM detection procedure and, depending on the BIOS, may come up with a CMOS error message. This particularly applies to AMI BIOS and occurs because the detected memory no longer matches the value stored in the CMOS setup program. Conversely, on some types of BIOS (eg, Award), the extra memory is accommodated automatically and the machine will boot normally. If you do get a CMOS error message, enter the CMOS setup program (just follow the screen prompt to do this), select “Standard CMOS Setup” from the resulting menu, and hit <ENTER>. Your new extended memory value should now be displayed, along with various other settings that are stored here. Assuming all is correct, hit <ESC>, then use the down arrow key to select “Write To CMOS And Exit”, and press <ENTER>. Final­ly, press <Y> to answer “yes” to the question “Save CMOS Settings & Exit?”. The new extended memory value is now stored in the CMOS setup and the computer should now complete its boot-up procedure. The only difference now should be the extra memory and that, in turn, should mean slicker performance on those memory-hogSC ging applications. July 1995  65