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Memory Size and System Performance
The amount of memory in a PC has a significant impact on its overall performance. Using too little RAM can be the biggest anchor dragging down overall system speed. This is something that many PC users fail to realize; I will often see someone posting to USEnet saying that their PC is "too slow" and so they want to upgrade to a faster processor. Then I will find out they are trying to run multiple applications or high-end games under Windows 95 but have only 8 MB of RAM. In a situation like this, upgrading the processor is a waste of money until the system memory is brought up to a more reasonable level.
Strictly speaking, the amount of memory in the computer has no impact on the speed that the memory runs, nor on the speed that the processor, chipset, motherboard and other major system components run. However, this is only if all of the programs running on the PC fit into the system RAM! All multitasking operating systems use virtual memory, which lets the PC think it has more memory than the actual physical RAM; the extra virtual memory is stored in a swap file on the hard disk. When more programs and data are in use than physically fit in memory, the virtual memory manager swaps parts of memory to disk. This is described in detail in the section discussing virtual memory.
When the amount of virtual memory in use greatly exceeds the amount of real memory, the operating system spends a lot of time swapping pages of memory around, which greatly hampers performance. The reason is simple: the hard disk is thousands of times slower than the system memory, if not more. Remember that hard disk access time is measured in thousandths of a second; memory access time is measured in billionths of a second. This doesn't tell the whole story but it gives you a general idea of the difference.
Let's suppose you are running a word processor, spreadsheet and a calendar program on Windows 95 on a system with 8 MB of real system memory. The total amount of virtual memory required by the applications you are using combine to most likely about 24 MB, depending on what versions of the software you are using. Windows 95 itself needs about 8 MB for system tasks. Since you only have 8 MB of memory, this means basically every time you do anything, the PC will have to pause and swap information to disk before proceeding. If you were to increase your system RAM to 32 MB, you could hold most (if not all) of the data in memory and the hard disk would be quiet. The improvement in performance is dramatic.
The best way to understand the importance of having enough memory is to compare PCs with more memory and with less when running similar tasks. I have seen 80486DX2-66s that feel faster than Pentium 133s, when the 486 has 32 MB of memory and the Pentium has only 8 MB. (I'm not exaggerating.) Even though the Pentium has probably three times the raw power, it is wasted because the system is spending so much time thrashing to the hard disk (while the CPU figuratively twiddles its thumbs).
So how much memory do you need? This is not an easy question to answer. It depends entirely on what you are using the system for. If you are running a single DOS application on a slower PC, 4 MB can be sufficient as long as the application doesn't need more than that. Many high-end CAD or graphics workstations use 256 MB of RAM or more. The amount of memory needed by PCs continues to increase as programs and data get larger and larger. A few years ago, 8 MB was considered a configuration for a high-end system; last year this would have been considered "entry level"; today, it is considered totally unacceptable. The trend towards much larger quantities of RAM will continue in the future, since the price of RAM continues to drop dramatically, and is now in the environs of $1/MB.
Tip: Watch your hard disk LED.
If you see it come on and flicker rapidly when switching between tasks for example, this
probably means that your operating system is being forced to use virtual memory. If this
happens often, it is a clue that you may need more memory. (Note that when loading
programs or doing other obviously disk-intensive work, having the disk light come on does
not necessarily imply anything about virtual memory, of course.)
In general, more memory is better, however you have to watch out for the cacheability issue, since some PCs will not cache memory above a certain value. In addition, the law of diminishing returns definitely applies to memory size: each time you increase your system's memory, you get less improvement than you did the previous time you increased it. Going from 8 MB to 16 MB results in a huge performance increase for most Windows 95 users. Going from 16 to 24 MB results in some improvement but much less than that resulting from going from 8 to 16, and so on.
For most systems, there is a point beyond which adding more memory does not add appreciably to system performance. Where this point lies depends a great deal on what you use your system for--if you are using huge multimedia files for example your PC can probably make use of as much memory as you can throw at it. For most users the point of serious diminishing returns lies between 24 and 48 MB. Above about 48 MB, you will not see much noticeable improvement unless you are doing high-end graphics work, manipulating large files, or multitasking like crazy.
The table below shows some sample operating systems and application types, along with general ranges for recommended memory. This is a guideline only and should not be taken as definitive law; if you are using Windows NT and several applications, I can guarantee that 32 MB is going to be too little, pretty quickly. Only you can assess how you use your PC and therefore what makes the most sense. (That said, I will also say that very few people will want to be below the numbers in the "minimum" column below):
There is one other way that memory size impacts on overall system performance. Having more memory allows you to dedicate some of it for use as a disk cache. A disk cache lets you store recently-used information from the disk in a special area of memory, to save time reading to the disk when it is needed again. This improves system performance by avoiding unnecessary reads and writes to the slow hard disk.
Next: Memory Packaging