Memory Speak
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Memory Explained
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<a href="#top"><img src="hhmemory_files/uparrow.gif" alt="top" border="0" height="16" width="17"></a> <a name="how">How Memory Works</a><a name="how"></a>In order to enable computers to work faster, there are several types of memory available today. Within a single computer there is no longer just one type of memory. Because the types of memory relate to speed, it is important to understand the differences when comparing the components of a computer. So get your memory ready as the following will explain what all those crazy abbreviations mean. But first, here is a brief description of how memory works.
<a href="#top"><img src="hhmemory_files/uparrow.gif" alt="top" border="0" height="16" width="17"></a> <a name="components"></a>Module Components<a name="pcb"></a>PCB (Printed Circuit Board)The green board that holds the memory chips is made up of several layers. Each layer contains <a href="#traces">traces</a> and circuitry to control the movement of data. Usually, higher quality memory modules use more layers. The more layers, the more space there is between traces. With more space between traces, the module has less chance of noise interference and is more reliable. <a name="traces"></a>Traces (Internal Trace Layer)Think of traces as roads that data travels on. The width and curvature as well as the distance between affect both the speed and reliability. Contact FingersThe contact fingers (connections or leads) are used to plug the memory chips into the module. Contacts can either be tin or gold. Gold is a better conductor than tin, but more expensive. To help avoid corrosion, It's always best to match the metal of the module to the metal of the socket. Chip PackagingThis is the material coating around the actual silicon. Today's most common packaging are. . .
Chip StackingFor higher capacity modules, it is necessary to stack chips on top of one another. Stacking can be internally (not visible) or externally (visible). <a href="#top"><img src="hhmemory_files/uparrow.gif" alt="top" border="0" height="16" width="17"></a> <a name="type"></a>Memory Types<a name="simm"></a>SIMM (Single In-line Memory Modules)SIMMs are used to store a single row of <a href="#dram">DRAM</a>, <a href="#edo">EDO</a> or <a href="#bedo">BEDO</a> chips where the module is soldered onto a <a href="#pcb">PCB</a>. One SIMM can contain several chips. When you add more memory to a computer, most likely you are adding a SIMM. The first SIMMs transferred 8 bits of data at a time and contained 30 pins. When CPU's began to read 32-bit chunks, a wider SIMM was developed and contained 72 pins. 72 pin SIMMS are 3/4" longer than 30 pin SIMMs and have a notch in the lower middle of the PCB. 72 pin SIMMs install at a slight angle. <a name="dimm"></a>DIMM (Dual In-line Memory Modules)DIMMs allow the ability to have two rows of <a href="#dram">DRAM</a>, <a href="#edo">EDO</a> or <a href="#bedo">BEDO</a> chips. They are able to contain twice as much memory on the same size circuit board. DIMMs contain 168 pins and transfer data in 64 bit chunks. DIMMs install straight up and down and have two notches on the bottom of the <a href="#pcb">PCB</a>. <a name="sodimm"></a>SO DIMM (Small Outline DIMM)SO DIMMs are commonly used in notebooks and are smaller than normal <a href="#dimm">DIMMs</a>. There are two types of SO DIMMs. Either 72 pins and a transfer rate of 32 bits or 144 pins with a transfer rate of 64 bits. <a name="rimm"></a>RDRAM - RIMMRambus, Inc, in conjunction with Intel has created new technology, Direct RDRAM, to increase the access speed for memory. RIMMs appeared on motherboards sometime during 1999. The in-line memory modules are called RIMMs. They have 184 pins and provide 1.6 GB per second of peak bandwidth in 16 bit chunks. As chip speed gets faster, so does the access to memory and the amount of heat produced. An aluminum sheath, called a heat spreader, covers the module to protect the chips from overheating. <a name="sorimm"></a>SO RIMMSimilar in appearance to a <a href="#sodimm">SO DIMM</a> and uses Rambus technology. <a href="#top"><img src="hhmemory_files/uparrow.gif" alt="top" border="0" height="16" width="17"></a> <a name="technology"></a>Technology<a name="dram"></a>DRAM (Dynamic Random Access Memory)One of the most common types of computer memory (RAM). It can only hold data for a short period of time and must be refreshed periodically. DRAMs are measured by storage capability and access time.
<a name="fpm"></a>FPM (Fast Page Mode)At one time, this was the most common and was often just referred to as <a href="#dram">DRAM</a>. It offered faster access to data located within the same row. <a name="edo"></a>EDO (Extended Data Out)Newer than <a href="#dram">DRAM</a> (1995) and requires only one CPU wait state. You can gain a 10 to 15% improvement in performance with EDO memory. <a name="bedo"></a>BEDO (Burst Extended Data Out)A step up from the EDO chips. It requires zero wait states and provides at least another 13 percent increase in performance. <a name="sdram"></a>SDRAM (Static RAM)Introduced in late 1996, retains memory and does not require refreshing. It synchronizes itself with the timing of the CPU. It also takes advantage of <a href="#interleave">interleaving</a> and burst mode functions. SDRAM is faster and more expensive than <a href="#dram">DRAM</a>. It comes in speeds of 66, 100, 133, 200, and 266MHz. <a name="ddrsdram"></a>DDR SDRAM (Double Data Rate Synchronous DRAM)Allows transactions on both the rising and falling edges of the <a href="#clock">clock cycle</a>. It has a <a href="#bus">bus</a> clock speed of 100MHz and will yield an effective data transfer rate of 200MHz. Direct RambusExtraordinarily fast. By using <a href="#clock">doubled clocked</a> provides a transfer rate up to 1.6GBs yielding a 800MHz speed over a narrow 16 bit bus. <a href="#cache">Cache</a> RAMThis is where <a href="#sram">SRAM</a> is used for storing information required by the CPU. It is in kilobyte sizes of 128KB, 256KB, etc. Other Memory Types
<a href="#top"><img src="hhmemory_files/uparrow.gif" alt="top" border="0" height="16" width="17"></a> <a name="evolution"></a>Evolution of Memory<tbody> </tbody>
<a href="#top"><img src="hhmemory_files/uparrow.gif" alt="top" border="0" height="16" width="17"></a> <a name="error"></a>Error CheckingIn order to ensure that memory is working correctly, data integrity, there are two primary means - parity and error correction code (ECC) or no checking at all - non-parity. ParityThis is the most common used method. It can detect errors, but not correct them. ECC (Error Correction Code)ECC can detect and correct single-bit errors. It is used in high-end PC's and servers. Non-ParityBecause there has been an increased quality of memory components and an infrequency of errors, more and more manufacturers do no include error checking capabilities. This also lowers the cost of the PC. <a href="#top"><img src="hhmemory_files/uparrow.gif" alt="top" border="0" height="16" width="17"></a> <a name="speed"></a>Speed - Access Time, Megahertz (MHz), Bytes Per SecondPrior to <a href="#sdram">SDRAM</a>, speed was expressed in terms of nanoseconds (ns). This measured the amount of time it takes the module to deliver a data request. Therefore, the lower the nanosecond speed, the faster. Typical speeds were 90, 80, 70 and 60ns. Older 486 machines may have 80 or 90. More recent Pentiums will have 60 or 70. Often, the last digit of a memory part number will represents the speed such as -6 = 60ns. <a href="#sdram">SDRAM</a> speed is measured in megahertz (MHz). Speed markings on the memory chips may still specific nanoseconds, but in this case in represents the number of nanoseconds between clock cycles. To add to the confusion the markings on t he chips don't match the Mhz value. Here is a conversion chart. <tbody> </tbody>
To calculate bytes per second you need to know the Bus Width and Bus Speed of your PC. The first thing to remember is 8-bits = 1 byte. If you have a 64-bit bus, than 8 bytes of information can be transferred at one time. (64 / 8 bits = 8 bytes) If your bus speed is 100Mhz (100 million clock cycles per second) and the bus width is 1 byte wide, the speed is 100 MB's per second. With a 64-bit width, the speed is 800 MBs per second (64 / 8 * 100,000,000) Rambus modules are measured in megabytes per second. Rambus modules are either 400 or 300Mhz. Because they send two pieces of information every clock cycle, you get 800 or 600Mhz. They have a 16-bit bus width or 2 bytes (16/8). The 400Mhz module speed is 1600MB a second or 1.6GB a second. (400,000,000 * 2) * 2. The 300Mhz module provides 1.2GBs a second. <a href="#top"><img src="hhmemory_files/uparrow.gif" alt="top" border="0" height="16" width="17"></a> <a name="adding">Adding Memory</a>If you are running
Windows 95 or 98, a minimum of 16 MBs of memory is necessary. If
you have several applications open at once, you will find by increasing
your memory, everything will run faster. Currently the cost for adding
additional memory is very low. Installation of memory is also fairly
simple. It does not require any reconfiguration.The difficult
part is determining what type of memory you need. <a href="#Type">Type</a> | <a href="#Sockets">Socket</a> | <a href="#Amount">Amount</a> More information on memory
determination...
<a href="#top"><img src="hhmemory_files/uparrow.gif" alt="top" border="0" height="16" width="17"></a> <a name="recommended">Recommended Memory</a>To help you determine the amount of minimum recommended memory for different versions of Windows, we have prepared this handy chart. Bottom Line - The more memory the better
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