Adding Random Access Memory (RAM) to your IBM Aptiva |
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Random Access Memory (RAM) is memory
where data is entered and retrieved. RAM is dynamic and volatile memory
that is emptied when the power is turned OFF. This is the memory that
holds programs and data while they are in use. This, in return,
increases overall system performance. Memory modules are available in
either SIMMs (Single Inline Memory Module) or DIMMs (Dual Inline Memory
Module). Before purchasing RAM modules to install in your computer, check your Aptiva Hardware Handbook to verify the correct type of RAM you need. Use the following outline as a guide:
How much RAM do you need? Highlights - The amount of RAM is critical to overall system performance. - There are several types of RAM, each providing different capabilities. - L2 cache is an important element in memory performance. - Parity and ECC memory, which can detect errors, are essential for high-end computing and servers. - IBM uses several different types of RAM depending on how the system is to be used. Overview Computer system performance is determined by a combination of factors working in tandem to achieve the efficient results people have come to expect from even basic computer systems. In the early stages of the buying cycle, processor speeds typically get the most attention, but they are actually only one consideration in overall system performance. In addition to determining processor speed and hard drive size requirements, understanding the complexities of RAM (random access memory) is critical. RAM is the component that handles the executable tasks of any application. When an application is recalled from the hard drive, the program is put into the RAM and is ready to be used. The amount of RAM in a system has a large effect on the speed in which it will run an application. The more RAM available, the less the processor has to access the hard drive, because more instructions can be carried out by the main memory instead of temporarily holding them in the hard drive. Thus, system performance is increased. In fact, in some configurations, a system with more RAM will run faster than the same system with a faster processor, but with less RAM. There is a 53% increase in system performance in the 75MHz system and a 74% increase in the 100MHz system. Interestingly, increasing memory from 16MB to 32MB will only realize a gain of approximately 1% to 2% . Therefore, doubling memory does not automatically double performance. In every system, there is a saturation point in which the cost of adding more RAM outweighs the performance gains realized. For many people, especially someone running complex applications such as CAD/CAE, large amounts of RAM above 16MB are needed, but there is still a saturation point. It should be remembered, however, that there are many different types of memory available for use in computer systems. Therefore, the focus of this brief will be to explain the important differences between memory types. IBM, in fact, uses several different types, offering different performance characteristics and error-checking capabilities. Types of Memory Computer memory falls within two broad groups: SRAM and DRAM. SRAM, or Static Random Access Memory, is faster but more expensive and is mainly used in L2 cache. (L2 cache will be discussed later in this brief.) DRAM, or Dynamic Random Access Memory, is slightly slower but less expensive and is used as the main memory for all systems today. Video Memory is used in graphics subsystems and will not be discussed in this brief. There are two main types of DRAM technology: Fast-page and EDO (Extended Data Out). The RAM can be fixed as parity, nonparity, ECC (Error Checking and Correcting), or EOS (ECC on SIMM) RAM. DRAM DRAM must be refreshed constantly so the charges that hold the bits of information can build up and stabilize. This "refreshing" causes delays between access of information, but has little effect on total system throughput because 486 and Pentium processors run at much faster speeds. Fast-page memory is a type of DRAM that allows for repeated memory accesses with minimum waiting for the next instruction. EDO is one of the newest memory technologies and can provide approximately a 5-30% boost in the memory subsystem speed. Also known as hyper-page mode memory, EDO provides increased performance by loading data at the same time it is searching for new information. Fast-page memory has to wait between this operation, thus causing delays. EDO is important because the new, high-speed processors need to get data quickly. Fast-page memory generally cannot deliver the data quickly enough; hence, more systems are incorporating EDO memory. However, a high-performance computer system must be designed to take advantage of EDO memory to realize the benefits. Parity and Non-Parity The benefit of incorporating parity memory in a system is the ability to detect single-bit errors and halt the system. With many business users dependent upon the accuracy of the data being processed, incorporating parity memory is a very important consideration. Most IBM PC 700 models use parity memory because of the extra protection that parity memory provides. Parity memory does not significantly add much to the total cost of memory modules, so the extra protection is worth the minimal cost. For mobile and desktop computing, however, the trend is for non-parity. Non-parity memory provides no error detection or correction. Parity memory chips can be added to systems that have a parity-supporting memory controller if error detection capabilities are needed. Error Checking and Correcting ECC memory takes parity memory capabilities one step further by automatically correcting single-bit errors, which account for 98% of all errors, without halting the system. In addition, the system will halt when 2-, 3-, or 4-bit errors are detected. ECC memory requires more overhead than parity memory for storing data and causes approximately a 3% performance degradation in the memory subsystem, but the resulting error detection and correction can make the tradeoff well worth it. Because of the extra protection ECC provides, it is utilized on the IBM PC Servers 500, 520 and 720, as well as on some PC Server 320 models. © IBM Corp |
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