Different RAM Types and its uses.doc
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Different RAM Types and its uses Intro The type of RAM doesn't matter nearly as much as how much of it you've got, but using plain old SDRAM memory today will slow you down. There are three main types of RAM SDRAM, DDR and Rambus DRAM. SDRAM (Synchronous DRAM) Almost all systems used to ship with !.! volt, "#$%pin SDRAM D&MMs. SDRAM is not an e'tension of older (D) DRAM but a new type of DRAM altogether. SDRAM started out running at ## M*+, while older fast page mode DRAM and (D) ma' out at ,- M*+. SDRAM is able to scale to "!! M*+ ./0"!!1 officially, and unofficially up to "$-M*+ or higher. As processors get faster, new generations of memory such as DDR and RDRAM are re2uired to get proper performance. DDR (Double Data Rate SDRAM) DDR basically doubles the rate of data transfer of standard SDRAM by transferring data on the up and down tic3 of a cloc3 cycle. DDR memory operating at !!!M*+ actually operates at "##M*+ 4 5 .a3a /0!!! 6 /057--1 or "!!M*+45 ./05## 6 /05"--1. DDR is a 5., volt technology that uses "$8 pins in its D&MMs. &t is incompatible with SDRAM physically, but uses a similar parallel bus, ma3ing it easier to implement than RDRAM, which is a different technology. Rambus DRAM (RDRAM) Despite it's higher price, &ntel has given RDRAM it's blessing for the consumer mar3et, and it will be the sole choice of memory for &ntel's /entium 8. RDRAM is a serial memory technology that arrived in three flavors, /0#--, /07--, and /0$--. /0$-- RDRAM has double the ma'imum throughput of old /0"-- SDRAM, but a higher latency. RDRAM designs with multiple channels, such as those in /entium 8 motherboards, are currently at the top of the heap in memory throughput, especially when paired with /0"-## RDRAM memory. DIMMs vs. RIMMs DRAM comes in two ma9or form factors D&MMs and R&MMS. D&MMs are #8%bit components, but if used in a motherboard with a dual%channel configuration .li3e with an :vidia n;orce chipset1 you must pair them to get ma'imum performance. So far there aren't many DDR chipset that use dual%channels. Typically, if you want to add ,"5 M< of D&MM memory to your machine, you 9ust pop in a ,"5 M< D&MM if you've got an available slot. D&MMs for SDRAM and DDR are different, and not physically compatible. SDRAM D&MMs have "#$%pins and run at !.! volts, while DDR D&MMs have "$8%pins and run at 5., volts. R&MMs use only a "#%bit interface but run at higher speeds than DDR. To get ma'imum performance, &ntel RDRAM chipsets re2uire the use of R&MMs in pairs over a dual%channel !5%bit interface. =ou have to plan more when upgrading and purchasing RDRAM.
From the top SIMM! DIMM and S"DIMM memory modules Memory Speed SDRAM initially shipped at a speed of ##M*+. As memory buses got faster, it was pumped up to "--M*+, and then "!!M*+. The speed grades are referred to as /0## .unofficially1, /0"-- and /0"!! SDRAM respectively. Some manufacturers are shipping a /0",- speed grade. *owever, this is an unofficial speed rating, and of little use unless you plan to overcloc3 your system. DDR comes in /0"#--, /05"--, /057-- and /0!5-- D&MMs. A /0"#-- D&MM is made up of /05-- DDR chips, while a /05"-- D&MM is made up of /05## chips. /057-- uses /0!!! DDR chips and /0!5-- uses /08-- chips that haven't gained widespread support. >o for /057-DDR. &t is about the cost of /05"-- memory and will give you better performance. RDRAM comes in /0#--, /07--, /0$-- and /0"-## speeds. >o for /0"-## RDRAM if you can find it. &f you can't, /0$-- RDRAM is widely available. #AS $atency SDRAM comes with latency ratings or ?0AS .0olumn Address Strobe1 latency? ratings. Standard /0"-- 6 /0"!! SDRAM comes in 0AS 5 or 0AS ! speed ratings. The lower latency of 0AS 5 memory will give you more performance. &t also costs a bit more, but it's worth it. DDR memory comes in 0AS 5 and 0AS 5., ratings, with 0AS 5 costing more and performing better. RDRAM has no 0AS latency ratings, but may eventually come in !5 and 8 ban3 forms with !5% ban3 RDRAM costing more and performing better. ;or now, it's all !5%ban3 RDRAM. %nderstandin& #ache
0ache Memory is fast memory that serves as a buffer between the processor and main memory. The cache holds data that was recently used by the processor and saves a trip all the way bac3 to slower main memory. The memory structure of /0s is often thought of as 9ust main memory, but it's really a five or si' level structure The first two levels of memory are contained in the processor itself, consisting of the processor's small internal memory, or re&isters, and $' cache, which is the first level of cache, usually contained in the processor. The third level of memory is the $( cache, usually contained on the motherboard. *owever, the 0eleron chip from &ntel actually contains "5$@ of A5 cache within the form factor of the chip. More and more chip ma3ers are planning to put this cache on board the processor itself. The benefit is that it will then run at the same speed as the processor, and cost less to put on the chip than to set up a bus and logic e'ternally from the processor. The fourth level, is being referred to as $) cache. This cache used to be the A5 cache on the motherboard, but now that some processors include A" and A5 cache on the chip, it becomes A! cache. Bsually, it runs slower than the processor, but faster than main memory. The fifth level .or fourth if you have no ?A! cache?1 of memory is the main memory itself. The si'th level is a piece of the hard dis3 used by the )perating System, usually called virtual memory. Most operating systems use this when they run out of main memory, but some use it in other ways as well. This si'%tiered structure is designed to efficiently speed data to the processor when it needs it, and also to allow the operating system to function when levels of main memory are low. =ou might as3, ?Chy is all this necessaryD? The answer is cost. &f there were one type of super%fast, super%cheap memory, it could theoretically satisfy the needs of this entire memory architecture. This will probably never happen since you don't need very much cache memory to drastically improve performance, and there will always be a faster, more e'pensive alternative to the current form of main memory. Memory Redundancy )ne important aspect to consider in memory is what level of redundancy you want. There are a few different levels of redundancy available in memory. Depending on your motherboard, it may support all or some of these types of memory The cheapest and most prevalent level of redundancy is non*parity memory. Chen you have non%parity memory in your machine and it encounters a memory error, the operating system will have no way of 3nowing and will most li3ely crash, but could corrupt data as well with no way of telling the )S. This is the most common type of memory, and unless specified, that's what you're getting. &t wor3s fine for most applications, but & wouldn't run life support systems on it. The second level of redundancy is parity memory .also called true parity1. /arity memory has e'tra chips that act as parity chips. Thus, the chip will be able to detect when a memory error has occurred and signal the operating system. =ou'll probably still crash, but at least you'll 3now why. The third level of redundancy is +## .(rror 0hec3ing and 0orrecting1. This re2uires even more logic and is usually more e'pensive. :ot only does it detect memory errors, but it also corrects "% bit (00 errors. &f you have a 5%bit error, you will still have some problems. Some motherboards enable you to have (00 memory.
"lder memory types
Fast Page Mode DRAM ;ast /age Mode DRAM is plain old DRAM as we once 3new it. The problem with standard DRAM was that it ma'es out at about ,- M*+. EDO DRAM (D) DRAM gave people up to ,E system performance increase over DRAM. (D) DRAM is li3e ;/M DRAM with some cache built into the chip. Ai3e ;/M DRAM, (D) DRAM ma'es out at about ,- M*+. (arly on, some system ma3ers claimed that if you used (D) DRAM you didn't need A5 cache in your computer to get decent performance. They were wrong. &t turns out that (D) DRAM wor3s along with A5 cache to ma3e things even faster, but if you lose the A5 cache, you lose a lot of speed.
RAM Memory Technolo&y
Memory Types
&n order to enable computers to wor3 faster, there are several types of memory available today. Cithin a single computer there is no longer 9ust one type of memory. <ecause the types of memory relate to speed, it is important to understand the differences when comparing the components of a computer.
S&MM .Single &n%line Memory Modules1 S&MMs are used to store a single row of DRAM, (D) or <(D) chips where the module is soldered onto a /0<. )ne S&MM can contain several chips. Chen you add more memory to a computer, most li3ely you are adding a S&MM.
The first S&MMs transferred $ bits of data at a time and contained !- pins. Chen 0/B's began to read !5%bit chun3s, a wider S&MM was developed and contained 75 pins.
75 pin S&MMS are !68? longer than !- pin S&MMs and have a notch in the lower middle of the /0<. 75 pin S&MMs install at a slight angle.
D&MM .Dual &n%line Memory Modules1 D&MMs allow the ability to have two rows of DRAM, (D) or <(D) chips. They are able to contain twice as much memory on the same si+e circuit board. D&MMs contain "#$ pins and transfer data in #8 bit chun3s. D&MMs install straight up and down and have two notches on the bottom of the /0<.
S)D&MM .Small )utline D&MM1 S) D&MMs are commonly used in noteboo3s and are smaller than normal D&MMs. There are two types of S) D&MMs. (ither 75 pins and a transfer rate of !5 bits or "88 pins with a transfer rate of #8 bits.
RDRAM % R&MM Rambus, &nc, in con9unction with &ntel has created new technology, Direct RDRAM, to increase the access speed for memory. R&MMs appeared on motherboards sometime during "FFF. The in% line memory modules are called R&MMs. They have "$8 pins and provide ".# >< per second of pea3 bandwidth in "# bit chun3s. As chip speed gets faster, so does the access to memory and the amount of heat produced. An aluminum sheath, called a heat spreader, covers the module to protect the chips from overheating. S) R&MM Similar in appearance to a technology. Technology DRAM .Dynamic Random )ne of the most common &t can only hold data for a refreshed periodically. capability and access time. Storage is rated in Access Memory1 types of computer memory .RAM1. short period of time and must be DRAMs are measured by storage megabytes .$ M<, "# M<, etc1. nanoseconds .#-ns, 7-ns, $-ns, amount of time to save or return DRAM, it would re2uire #save or return information. The faster the memory operates. two a 0/B read wait or states write for operation each at e'ecution. one time. S)D&MM and uses Rambus
Access time is rated in etc1 and represents the information. Cith a #-ns billionths of a second to lower the nanospeed, the DRAM 0an chips only re2uire
e'ecute
either
;/M .;ast /age Mode1 At one time, this was the most common and was often 9ust referred to as DRAM. &t offered faster access to data located within the same row. (D) .('tended Data )ut1 :ewer than DRAM ."FF,1 and re2uires only one 0/B wait state. =ou can gain a "- to ",E improvement in performance with (D) memory. <(D) .<urst ('tended Data )ut1 A step up from the (D) chips. &t re2uires +ero wait states and provides at least another "! percent increase in performance. SDRAM .Static RAM1 &ntroduced in late "FF#, retains memory and does not re2uire refreshing. &t synchroni+es itself
with the timing of the 0/B. &t also ta3es advantage of interleaving and burst mode functions. SDRAM is faster and more e'pensive than DRAM. &t comes in speeds of ##, "--, "!!, 5--, and 5##M*+. DDR SDRAM .Double Data Rate Synchronous DRAM1 Allows transactions on both the rising and falling edges of the cloc3 cycle. &t has a bus cloc3 speed of "--M*+ and will yield an effective data transfer rate of 5--M*+. Direct Rambus ('traordinarily fast. <y using doubled cloc3ed provides a transfer rate up to ".#><s yielding a $--M*+ speed over a narrow "# bit bus. 0ache RAM This is where SRAM is used for storing information re2uired by the 0/B. &t is in 3ilobyte si+es of "5$@<, 5,#@<, etc. )ther Memory Types GRAM .Gideo RAM1 GRAM is a video version of ;/M and is most often used in video accelerator cards. <ecause it has two ports, &t provides the e'tra benefit over DRAM of being able to e'ecute simultaneous read6write operations at the same time. )ne channel is used to refresh the screen and the other manages image changes. GRAM tends to be more e'pensive. ;lash Memory This is a solid%state, nonvolatile, rewritable memory that functions li3e RAM and a hard dis3 combined. &f power is lost, all data remains in memory. <ecause of its high speed, durability, and low voltage re2uirements, it is ideal for digital cameras, cell phones, printers, handheld computers, pagers and audio recorders. Shadow RAM Chen your computer starts up .boots1, minimal instructions for performing the startup procedures and video controls are stored in R)M .Read )nly Memory1 in what is commonly called <&)S. R)M e'ecutes slowly. Shadow RAM allows for the capability of moving selected parts of the <&)S code from R)M to the faster RAM memory. Determinin& your #omputer RAM Type 0urrently the cost for adding additional memory is very low. &nstallation of memory is also fairly simple. &t does not re2uire any reconfiguration. The difficult part is determinin& ,hat type of memory you need. Type • • F-M H ;ast /age % &f you have a 8$#, you probably have ;/M +D" H ('tended Data )ut % &f you have an early /entium system, you probably have (D) SDRAM % &f you have a /entium or 0eleron system purchased in "FFF, you probably have SDRAM
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Soc.ets Memory modules plug into a soc3et on the motherboard. There are three soc3et types.
• • •
SIMM H )/ pin H ! inches in length SIMM 0 1( pin H 8 inches in length DIMM H '23 pin H , inches in length
Most older 8$# machines will use !- pin modules. Aater model 8$# and /entium machines will probably use 75 pin modules. More recent /entium machines may have "#$ pin.
Amount Memory si+es increase by the power of 5. This results in si+es of ", 5, 8, $, "#, !5, #8, "5$, 5,# M<s. • • • • )n some older 8$# machines, one memory module can be added at a time. )n most /entium machines, modules must be added in pairs. (ach pair must be of the same si+e. SDRAM modules can be added one at a time.
;or e'ample, if you have $ M<s of memory on a /entium, you have two 8 M< modules. To increase to "# M<s, you need to add two more 8 M< modules. To increase to 58 M<s, you need to add two $ M< modules. $oo.in& Inside :ow that you 3now the parameters, how do you determine which type you needD Aoo3ing inside the computer will not provide all of the information. &t will confirm how many modules you currently have. =ou can also confirm the type and 2uantity of open soc3ets. &f you only have four soc3ets and each soc3et contains a module, you will have to replace some of the e'isting memory modules. #hec. the Manual The other place to find the correct information is your ownerIs manual. The manufacturer should have listed the type of memory re2uired. =ou will need to determine the parity and speed. Identification :ow that you have the necessary information, you find an ad for memory and still you may not be able to determine which modules you need. ChyD <ecause the computer industry thrives on confusion and abbreviations. *ereIs how to interpret the coding scheme. 30 pin modules For 30 pin modules you will see something like
• • •
" ' F%#8 ' F%78 ' $%7-
The first number is the si+e in M<Is. &n our e'ample this would be "M< or 8M<. The second number represents parity. The value F represents parity and $ represents non% parity. .)f course that ma3es a lot of senseJ1 The F or $ also identifies that it is a !- pin module. The third value represents the speed. 72 pin modules For 72 pin modules you will see something like • • • • " ' !5%#5 ' !5%78 ' !#%#$ ' !#%7-
Kust li3e the !- pin modules, the first value represents the si+e, (L0(/T it only represents M of the total memory si+e. DonIt as3 why, 9ust accept it. So the value of 8 represents a "# M< .8 ' 81 module. A value of $ represents a !5 M< .8 ' $1 module. The second value, again 9ust li3e the !- pin, represents parity and the number of pins. !# is used for parity and !5 for non%parity. =ou arenIt as3ing why again, are youD The third value represents the speed, the same as the !- pin. memory re4uirement for "peratin& system 5indo,s 67 % Seems to be happy with #8 M<. Anything over doesn't get you much performance increase, but if you have anything less, &'d seriously consider getting more memory. The benefit can be 2uite substantial. 5indo,s 638Me % Seems to be happy with "5$ M<. Cor3s o3 with #8 M<, but you will probably see a significant performance increase by going to "5$. Anything over "5$ generally doesn't get you much. 5indo,s 9T (5or.station) % Seems to be happy with "5$ M< for most things. 5indo,s 9T (Server) % 0an run with "5$ M<, but more is better. Definitely consider getting 5,# M< or more if this server is going to have a heavy demand on it. 5indo,s (/// % At least "5$ M<, and basically as much as you can throw at it. Seriously consider 5,# M< or more if it's got a heavy demand on it.
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5indo,s :- % *ard to say, but 5,# M< minimum, and almost certainly would wor3 better with more.
5hat are the benefits of up&radin& your computers memory; Bpgrading your memory is typically the easiest and least e'pensive way to upgrade your computer for a significant boost in performance. The computer's RAM memory is its wor3space, or where all of the instructions it needs to act on are stored temporarily. Thin3 of the RAM as the des3 you use to sort through your wor3. &f the si+e of that des3 is small, your efficiency is limited in comparison to a larger des3 that allows you to wor3 more effectively and efficiently. Similarly, a computer with more RAM can wor3 more efficiently because it does not need to retrieve information from the hard dis3 drive as often. A memory upgrade is particularly helpful for users who wor3 with large files, have more than one program open at one time, or use memory% intensive applications such as games or graphics and video editing software. <o, do you .no, it=s time for a memory up&rade; There are several signs indicating it may be time to upgrade your memory. &f you see your mouse pointer turn into an hourglass for significant periods of time, if you hear your hard drive wor3ing, or if your computer seems to wor3 more slowly than you e'pect, the reason is probably insufficient memory. Chen physical memory is insufficient, the system uses *ard Dis3 Space as memory. This is called ?Girtual Memory?. Since access time of /hysical memory is in tens of :anoSeconds and Access time of *ard Dis3 is in MilliSeconds, the system slows down considerably. 5hat=s the difference bet,een buffered and unbuffered DIMMs; *igh density D&MMs have lots of chips on them and therefore possess a higher capacitive load on the address and control signals in comparison to lower density D&MMs. Some designers use redrive buffers on the D&MM to boost the signals to reduce system loading when compared to the same high density module without buffers. <ut the buffers introduce a small delay into the electrical signal, so adding buffers to a standard density module would have the effect of slowing down the signal, compared to the same low density module without buffers. 5hat is >irtual Memory; This is a method of e'tending the available physical memory on a computer. &n a virtual memory system, the operating system creates a pagefile, or swapfile, and divides memory into units called pages. Recently referenced pages are located in physical memory, or RAM. &f a page of memory is not referenced for a while, it is written to the pagefile. This is called ?swapping? or ?paging out? memory. &f that piece of memory is then later referenced by a program, the operating system reads the memory page bac3 from the pagefile into physical memory, also called ?swapping? or ?paging in? memory. The total amount of memory that is available to programs is the amount of physical memory in the computer in addition to the si+e of the pagefile. 5ill addin& more RAM ma.e my Internet bro,sin& faster; Maybe. &nternet browsing speed depends on a huge number of factors, including your connection speed, traffic on the site you're visiting, and the other components in your system. =ou will probably notice the biggest improvement from additional RAM if are viewing or wor3ing with large files .such as photos and digital audio and video1 or if you switch between your browser and other applications often. 5hat=s the difference bet,een RDRAM and SDRAM;
RDRAM stands for Rambus Dynamic Random Access Memory. SDRAM stands for Synchronous Dynamic Random Access Memory. The two memories are completely different memory technologies and are not compatible with each other. RDRAM is a uni2ue design developed by a company called Rambus, &nc. RDRAM is e'tremely fast and uses a narrow, high%bandwidth ?channel? to transmit data at speeds much faster than SDRAM. 5hat is the difference bet,een 1( bit and 2? bit memory; 75 bit memory is commonly 3nown as (00 memory. &t has an additional $ bits for (rror 0orrection 0hec3 #8 bit memory is non%(00. 75 bit or #8 bit configuration are typically found in "#$ pin D&MMs. Memory RAM Speed * Access Time! Me&ahert@ (M<@)! Aytes -er Second /rior to SDRAM, speed was e'pressed in terms of nanoseconds .ns1. This measured the amount of time it ta3es the module to deliver a data re2uest. Therefore, the lower the nanosecond speed, the faster. Typical speeds were F-, $-, 7- and #-ns. )lder 8$# machines may have $- or F-. More recent /entiums will have #- or 7-.
M<@ Speed ## "-"!!
Total #loc. Second ##,---,--"--,---,--"!!,---,---
#ycles
perDivide by ' billions to &et nanoseconds per cloc. speed. ", "$
)ften, the last digit of a memory part number will represents the speed such as %# N #-ns. SDRAM speed is measured in me&ahert@ (M<@). Speed mar3ings on the memory chips may still specific nanoseconds, but in this case in represents the number of nanoseconds between cloc3 cycles. To add to the confusion the mar3ings on the chips don't match the Mh+ value. *ere is a conversion chart. To calculate bytes per second you need to 3now the Aus 5idth and Aus Speed of your /0. The first thing to remember is $%bits N " byte. &f you have a #8%bit bus, than $ bytes of information can be transferred at one time. .#8 6 $ bits N $ bytes1 &f your bus speed is "--Mh+ ."-- million cloc3 cycles per second1 and the bus width is " byte wide, the speed is "-- M<'s per second. Cith a #8%bit width, the speed is $-- M<s per second .#8 6 $ 4 "--,---,---1 Rambus modules are measured in megabytes per second. Rambus modules are either 8-- or !--Mh+. <ecause they send two pieces of information every cloc3 cycle, you get $-- or #--Mh+. They have a "#%bit bus width or 5 bytes ."#6$1. The 8--Mh+ module speed is "#--M< a second or
".#>< a second. .8--,---,--- 4 51 4 5. The !--Mh+ module provides ".5><s a second.
From the top SIMM! DIMM and S"DIMM memory modules Memory Speed SDRAM initially shipped at a speed of ##M*+. As memory buses got faster, it was pumped up to "--M*+, and then "!!M*+. The speed grades are referred to as /0## .unofficially1, /0"-- and /0"!! SDRAM respectively. Some manufacturers are shipping a /0",- speed grade. *owever, this is an unofficial speed rating, and of little use unless you plan to overcloc3 your system. DDR comes in /0"#--, /05"--, /057-- and /0!5-- D&MMs. A /0"#-- D&MM is made up of /05-- DDR chips, while a /05"-- D&MM is made up of /05## chips. /057-- uses /0!!! DDR chips and /0!5-- uses /08-- chips that haven't gained widespread support. >o for /057-DDR. &t is about the cost of /05"-- memory and will give you better performance. RDRAM comes in /0#--, /07--, /0$-- and /0"-## speeds. >o for /0"-## RDRAM if you can find it. &f you can't, /0$-- RDRAM is widely available. #AS $atency SDRAM comes with latency ratings or ?0AS .0olumn Address Strobe1 latency? ratings. Standard /0"-- 6 /0"!! SDRAM comes in 0AS 5 or 0AS ! speed ratings. The lower latency of 0AS 5 memory will give you more performance. &t also costs a bit more, but it's worth it. DDR memory comes in 0AS 5 and 0AS 5., ratings, with 0AS 5 costing more and performing better. RDRAM has no 0AS latency ratings, but may eventually come in !5 and 8 ban3 forms with !5% ban3 RDRAM costing more and performing better. ;or now, it's all !5%ban3 RDRAM. %nderstandin& #ache
0ache Memory is fast memory that serves as a buffer between the processor and main memory. The cache holds data that was recently used by the processor and saves a trip all the way bac3 to slower main memory. The memory structure of /0s is often thought of as 9ust main memory, but it's really a five or si' level structure The first two levels of memory are contained in the processor itself, consisting of the processor's small internal memory, or re&isters, and $' cache, which is the first level of cache, usually contained in the processor. The third level of memory is the $( cache, usually contained on the motherboard. *owever, the 0eleron chip from &ntel actually contains "5$@ of A5 cache within the form factor of the chip. More and more chip ma3ers are planning to put this cache on board the processor itself. The benefit is that it will then run at the same speed as the processor, and cost less to put on the chip than to set up a bus and logic e'ternally from the processor. The fourth level, is being referred to as $) cache. This cache used to be the A5 cache on the motherboard, but now that some processors include A" and A5 cache on the chip, it becomes A! cache. Bsually, it runs slower than the processor, but faster than main memory. The fifth level .or fourth if you have no ?A! cache?1 of memory is the main memory itself. The si'th level is a piece of the hard dis3 used by the )perating System, usually called virtual memory. Most operating systems use this when they run out of main memory, but some use it in other ways as well. This si'%tiered structure is designed to efficiently speed data to the processor when it needs it, and also to allow the operating system to function when levels of main memory are low. =ou might as3, ?Chy is all this necessaryD? The answer is cost. &f there were one type of super%fast, super%cheap memory, it could theoretically satisfy the needs of this entire memory architecture. This will probably never happen since you don't need very much cache memory to drastically improve performance, and there will always be a faster, more e'pensive alternative to the current form of main memory. Memory Redundancy )ne important aspect to consider in memory is what level of redundancy you want. There are a few different levels of redundancy available in memory. Depending on your motherboard, it may support all or some of these types of memory The cheapest and most prevalent level of redundancy is non*parity memory. Chen you have non%parity memory in your machine and it encounters a memory error, the operating system will have no way of 3nowing and will most li3ely crash, but could corrupt data as well with no way of telling the )S. This is the most common type of memory, and unless specified, that's what you're getting. &t wor3s fine for most applications, but & wouldn't run life support systems on it. The second level of redundancy is parity memory .also called true parity1. /arity memory has e'tra chips that act as parity chips. Thus, the chip will be able to detect when a memory error has occurred and signal the operating system. =ou'll probably still crash, but at least you'll 3now why. The third level of redundancy is +## .(rror 0hec3ing and 0orrecting1. This re2uires even more logic and is usually more e'pensive. :ot only does it detect memory errors, but it also corrects "% bit (00 errors. &f you have a 5%bit error, you will still have some problems. Some motherboards enable you to have (00 memory.
"lder memory types
Fast Page Mode DRAM ;ast /age Mode DRAM is plain old DRAM as we once 3new it. The problem with standard DRAM was that it ma'es out at about ,- M*+. EDO DRAM (D) DRAM gave people up to ,E system performance increase over DRAM. (D) DRAM is li3e ;/M DRAM with some cache built into the chip. Ai3e ;/M DRAM, (D) DRAM ma'es out at about ,- M*+. (arly on, some system ma3ers claimed that if you used (D) DRAM you didn't need A5 cache in your computer to get decent performance. They were wrong. &t turns out that (D) DRAM wor3s along with A5 cache to ma3e things even faster, but if you lose the A5 cache, you lose a lot of speed.
RAM Memory Technolo&y
Memory Types
&n order to enable computers to wor3 faster, there are several types of memory available today. Cithin a single computer there is no longer 9ust one type of memory. <ecause the types of memory relate to speed, it is important to understand the differences when comparing the components of a computer.
S&MM .Single &n%line Memory Modules1 S&MMs are used to store a single row of DRAM, (D) or <(D) chips where the module is soldered onto a /0<. )ne S&MM can contain several chips. Chen you add more memory to a computer, most li3ely you are adding a S&MM.
The first S&MMs transferred $ bits of data at a time and contained !- pins. Chen 0/B's began to read !5%bit chun3s, a wider S&MM was developed and contained 75 pins.
75 pin S&MMS are !68? longer than !- pin S&MMs and have a notch in the lower middle of the /0<. 75 pin S&MMs install at a slight angle.
D&MM .Dual &n%line Memory Modules1 D&MMs allow the ability to have two rows of DRAM, (D) or <(D) chips. They are able to contain twice as much memory on the same si+e circuit board. D&MMs contain "#$ pins and transfer data in #8 bit chun3s. D&MMs install straight up and down and have two notches on the bottom of the /0<.
S)D&MM .Small )utline D&MM1 S) D&MMs are commonly used in noteboo3s and are smaller than normal D&MMs. There are two types of S) D&MMs. (ither 75 pins and a transfer rate of !5 bits or "88 pins with a transfer rate of #8 bits.
RDRAM % R&MM Rambus, &nc, in con9unction with &ntel has created new technology, Direct RDRAM, to increase the access speed for memory. R&MMs appeared on motherboards sometime during "FFF. The in% line memory modules are called R&MMs. They have "$8 pins and provide ".# >< per second of pea3 bandwidth in "# bit chun3s. As chip speed gets faster, so does the access to memory and the amount of heat produced. An aluminum sheath, called a heat spreader, covers the module to protect the chips from overheating. S) R&MM Similar in appearance to a technology. Technology DRAM .Dynamic Random )ne of the most common &t can only hold data for a refreshed periodically. capability and access time. Storage is rated in Access Memory1 types of computer memory .RAM1. short period of time and must be DRAMs are measured by storage megabytes .$ M<, "# M<, etc1. nanoseconds .#-ns, 7-ns, $-ns, amount of time to save or return DRAM, it would re2uire #save or return information. The faster the memory operates. two a 0/B read wait or states write for operation each at e'ecution. one time. S)D&MM and uses Rambus
Access time is rated in etc1 and represents the information. Cith a #-ns billionths of a second to lower the nanospeed, the DRAM 0an chips only re2uire
e'ecute
either
;/M .;ast /age Mode1 At one time, this was the most common and was often 9ust referred to as DRAM. &t offered faster access to data located within the same row. (D) .('tended Data )ut1 :ewer than DRAM ."FF,1 and re2uires only one 0/B wait state. =ou can gain a "- to ",E improvement in performance with (D) memory. <(D) .<urst ('tended Data )ut1 A step up from the (D) chips. &t re2uires +ero wait states and provides at least another "! percent increase in performance. SDRAM .Static RAM1 &ntroduced in late "FF#, retains memory and does not re2uire refreshing. &t synchroni+es itself
with the timing of the 0/B. &t also ta3es advantage of interleaving and burst mode functions. SDRAM is faster and more e'pensive than DRAM. &t comes in speeds of ##, "--, "!!, 5--, and 5##M*+. DDR SDRAM .Double Data Rate Synchronous DRAM1 Allows transactions on both the rising and falling edges of the cloc3 cycle. &t has a bus cloc3 speed of "--M*+ and will yield an effective data transfer rate of 5--M*+. Direct Rambus ('traordinarily fast. <y using doubled cloc3ed provides a transfer rate up to ".#><s yielding a $--M*+ speed over a narrow "# bit bus. 0ache RAM This is where SRAM is used for storing information re2uired by the 0/B. &t is in 3ilobyte si+es of "5$@<, 5,#@<, etc. )ther Memory Types GRAM .Gideo RAM1 GRAM is a video version of ;/M and is most often used in video accelerator cards. <ecause it has two ports, &t provides the e'tra benefit over DRAM of being able to e'ecute simultaneous read6write operations at the same time. )ne channel is used to refresh the screen and the other manages image changes. GRAM tends to be more e'pensive. ;lash Memory This is a solid%state, nonvolatile, rewritable memory that functions li3e RAM and a hard dis3 combined. &f power is lost, all data remains in memory. <ecause of its high speed, durability, and low voltage re2uirements, it is ideal for digital cameras, cell phones, printers, handheld computers, pagers and audio recorders. Shadow RAM Chen your computer starts up .boots1, minimal instructions for performing the startup procedures and video controls are stored in R)M .Read )nly Memory1 in what is commonly called <&)S. R)M e'ecutes slowly. Shadow RAM allows for the capability of moving selected parts of the <&)S code from R)M to the faster RAM memory. Determinin& your #omputer RAM Type 0urrently the cost for adding additional memory is very low. &nstallation of memory is also fairly simple. &t does not re2uire any reconfiguration. The difficult part is determinin& ,hat type of memory you need. Type • • F-M H ;ast /age % &f you have a 8$#, you probably have ;/M +D" H ('tended Data )ut % &f you have an early /entium system, you probably have (D) SDRAM % &f you have a /entium or 0eleron system purchased in "FFF, you probably have SDRAM
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Soc.ets Memory modules plug into a soc3et on the motherboard. There are three soc3et types.
• • •
SIMM H )/ pin H ! inches in length SIMM 0 1( pin H 8 inches in length DIMM H '23 pin H , inches in length
Most older 8$# machines will use !- pin modules. Aater model 8$# and /entium machines will probably use 75 pin modules. More recent /entium machines may have "#$ pin.
Amount Memory si+es increase by the power of 5. This results in si+es of ", 5, 8, $, "#, !5, #8, "5$, 5,# M<s. • • • • )n some older 8$# machines, one memory module can be added at a time. )n most /entium machines, modules must be added in pairs. (ach pair must be of the same si+e. SDRAM modules can be added one at a time.
;or e'ample, if you have $ M<s of memory on a /entium, you have two 8 M< modules. To increase to "# M<s, you need to add two more 8 M< modules. To increase to 58 M<s, you need to add two $ M< modules. $oo.in& Inside :ow that you 3now the parameters, how do you determine which type you needD Aoo3ing inside the computer will not provide all of the information. &t will confirm how many modules you currently have. =ou can also confirm the type and 2uantity of open soc3ets. &f you only have four soc3ets and each soc3et contains a module, you will have to replace some of the e'isting memory modules. #hec. the Manual The other place to find the correct information is your ownerIs manual. The manufacturer should have listed the type of memory re2uired. =ou will need to determine the parity and speed. Identification :ow that you have the necessary information, you find an ad for memory and still you may not be able to determine which modules you need. ChyD <ecause the computer industry thrives on confusion and abbreviations. *ereIs how to interpret the coding scheme. 30 pin modules For 30 pin modules you will see something like
• • •
" ' F%#8 ' F%78 ' $%7-
The first number is the si+e in M<Is. &n our e'ample this would be "M< or 8M<. The second number represents parity. The value F represents parity and $ represents non% parity. .)f course that ma3es a lot of senseJ1 The F or $ also identifies that it is a !- pin module. The third value represents the speed. 72 pin modules For 72 pin modules you will see something like • • • • " ' !5%#5 ' !5%78 ' !#%#$ ' !#%7-
Kust li3e the !- pin modules, the first value represents the si+e, (L0(/T it only represents M of the total memory si+e. DonIt as3 why, 9ust accept it. So the value of 8 represents a "# M< .8 ' 81 module. A value of $ represents a !5 M< .8 ' $1 module. The second value, again 9ust li3e the !- pin, represents parity and the number of pins. !# is used for parity and !5 for non%parity. =ou arenIt as3ing why again, are youD The third value represents the speed, the same as the !- pin. memory re4uirement for "peratin& system 5indo,s 67 % Seems to be happy with #8 M<. Anything over doesn't get you much performance increase, but if you have anything less, &'d seriously consider getting more memory. The benefit can be 2uite substantial. 5indo,s 638Me % Seems to be happy with "5$ M<. Cor3s o3 with #8 M<, but you will probably see a significant performance increase by going to "5$. Anything over "5$ generally doesn't get you much. 5indo,s 9T (5or.station) % Seems to be happy with "5$ M< for most things. 5indo,s 9T (Server) % 0an run with "5$ M<, but more is better. Definitely consider getting 5,# M< or more if this server is going to have a heavy demand on it. 5indo,s (/// % At least "5$ M<, and basically as much as you can throw at it. Seriously consider 5,# M< or more if it's got a heavy demand on it.
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5indo,s :- % *ard to say, but 5,# M< minimum, and almost certainly would wor3 better with more.
5hat are the benefits of up&radin& your computers memory; Bpgrading your memory is typically the easiest and least e'pensive way to upgrade your computer for a significant boost in performance. The computer's RAM memory is its wor3space, or where all of the instructions it needs to act on are stored temporarily. Thin3 of the RAM as the des3 you use to sort through your wor3. &f the si+e of that des3 is small, your efficiency is limited in comparison to a larger des3 that allows you to wor3 more effectively and efficiently. Similarly, a computer with more RAM can wor3 more efficiently because it does not need to retrieve information from the hard dis3 drive as often. A memory upgrade is particularly helpful for users who wor3 with large files, have more than one program open at one time, or use memory% intensive applications such as games or graphics and video editing software. <o, do you .no, it=s time for a memory up&rade; There are several signs indicating it may be time to upgrade your memory. &f you see your mouse pointer turn into an hourglass for significant periods of time, if you hear your hard drive wor3ing, or if your computer seems to wor3 more slowly than you e'pect, the reason is probably insufficient memory. Chen physical memory is insufficient, the system uses *ard Dis3 Space as memory. This is called ?Girtual Memory?. Since access time of /hysical memory is in tens of :anoSeconds and Access time of *ard Dis3 is in MilliSeconds, the system slows down considerably. 5hat=s the difference bet,een buffered and unbuffered DIMMs; *igh density D&MMs have lots of chips on them and therefore possess a higher capacitive load on the address and control signals in comparison to lower density D&MMs. Some designers use redrive buffers on the D&MM to boost the signals to reduce system loading when compared to the same high density module without buffers. <ut the buffers introduce a small delay into the electrical signal, so adding buffers to a standard density module would have the effect of slowing down the signal, compared to the same low density module without buffers. 5hat is >irtual Memory; This is a method of e'tending the available physical memory on a computer. &n a virtual memory system, the operating system creates a pagefile, or swapfile, and divides memory into units called pages. Recently referenced pages are located in physical memory, or RAM. &f a page of memory is not referenced for a while, it is written to the pagefile. This is called ?swapping? or ?paging out? memory. &f that piece of memory is then later referenced by a program, the operating system reads the memory page bac3 from the pagefile into physical memory, also called ?swapping? or ?paging in? memory. The total amount of memory that is available to programs is the amount of physical memory in the computer in addition to the si+e of the pagefile. 5ill addin& more RAM ma.e my Internet bro,sin& faster; Maybe. &nternet browsing speed depends on a huge number of factors, including your connection speed, traffic on the site you're visiting, and the other components in your system. =ou will probably notice the biggest improvement from additional RAM if are viewing or wor3ing with large files .such as photos and digital audio and video1 or if you switch between your browser and other applications often. 5hat=s the difference bet,een RDRAM and SDRAM;
RDRAM stands for Rambus Dynamic Random Access Memory. SDRAM stands for Synchronous Dynamic Random Access Memory. The two memories are completely different memory technologies and are not compatible with each other. RDRAM is a uni2ue design developed by a company called Rambus, &nc. RDRAM is e'tremely fast and uses a narrow, high%bandwidth ?channel? to transmit data at speeds much faster than SDRAM. 5hat is the difference bet,een 1( bit and 2? bit memory; 75 bit memory is commonly 3nown as (00 memory. &t has an additional $ bits for (rror 0orrection 0hec3 #8 bit memory is non%(00. 75 bit or #8 bit configuration are typically found in "#$ pin D&MMs. Memory RAM Speed * Access Time! Me&ahert@ (M<@)! Aytes -er Second /rior to SDRAM, speed was e'pressed in terms of nanoseconds .ns1. This measured the amount of time it ta3es the module to deliver a data re2uest. Therefore, the lower the nanosecond speed, the faster. Typical speeds were F-, $-, 7- and #-ns. )lder 8$# machines may have $- or F-. More recent /entiums will have #- or 7-.
M<@ Speed ## "-"!!
Total #loc. Second ##,---,--"--,---,--"!!,---,---
#ycles
perDivide by ' billions to &et nanoseconds per cloc. speed. ", "$
)ften, the last digit of a memory part number will represents the speed such as %# N #-ns. SDRAM speed is measured in me&ahert@ (M<@). Speed mar3ings on the memory chips may still specific nanoseconds, but in this case in represents the number of nanoseconds between cloc3 cycles. To add to the confusion the mar3ings on the chips don't match the Mh+ value. *ere is a conversion chart. To calculate bytes per second you need to 3now the Aus 5idth and Aus Speed of your /0. The first thing to remember is $%bits N " byte. &f you have a #8%bit bus, than $ bytes of information can be transferred at one time. .#8 6 $ bits N $ bytes1 &f your bus speed is "--Mh+ ."-- million cloc3 cycles per second1 and the bus width is " byte wide, the speed is "-- M<'s per second. Cith a #8%bit width, the speed is $-- M<s per second .#8 6 $ 4 "--,---,---1 Rambus modules are measured in megabytes per second. Rambus modules are either 8-- or !--Mh+. <ecause they send two pieces of information every cloc3 cycle, you get $-- or #--Mh+. They have a "#%bit bus width or 5 bytes ."#6$1. The 8--Mh+ module speed is "#--M< a second or
".#>< a second. .8--,---,--- 4 51 4 5. The !--Mh+ module provides ".5><s a second.
