Memory isaccessible in various physical packaging. Roughly in order of theirappearance, the major types of DRAM packaging include:DIP (Dual Inline Pin Package) This package comprises arectangular chip with a row of pins down each long side, making itresemble a pest. DIP was the a lot of common DRAM package offered in PCsthrough early 386 models. DIP chips were produced in Page Mode andQuick Page Setting, and also are long obsolete. DIP packaging was likewise usedfor L2 cache memory on most 486 and some Pentium-class motherboards.DIP DRAM is useless nowadays.SIPP (Single Inline Pin Package)This package transforms a DIP chip on its side and exhas a tendency all leadsright out one side, parallel to the plane of the chip. SIPPs wereintended to allow memory to be installed even more densely, and were usedin a couple of 386SX units, however they never before caught on. SIPPs were producedin Page Mode and Rapid Page Mode develop, and are long obsolete.SIMM (Single Inline Memory Module)This package mounts multiple individual DRAM DIP chips on a smallcircuit board via a card-edge connector designed to fit a socket onthe motherboard. Mainstream SIMMs have been produced in two formfactors:30-pinThese SIMMs were offered in a couple of 286systems, a lot of 386 systems, and some 486 units, and were created inPage Mode and also Quick Page Mode form. Although they are still available,30-pin SIMMs are obsolete. If you tear dvery own an old system, any 30-pinSIMMs you salvage are also tiny and also also slow-moving to be helpful. However before,some laser printers execute usage them.72-pinThese SIMMs were offered in some 386 units,the majority of 486 systems, and also almost all Pentium-class systems developed beforethe development of DIMMs. 72-pin SIMMs were developed in Rapid Page Mode,EDO develop, and BEDO develop. When tearing dvery own old units, 72-pin SIMMsmay be worth salvaging, as they can be provided to expand the memory on alate-model Pentium or Pentium Pro system or to expand also the memory insome laser printers.Figure 5-1 mirrors a 72-pin SIMM (top) and also a 30-pinSIMM. The 72-pin SIMM is keyed by the notch at the bottom right; the30-pin SIMM by the notch at the bottom left. The holes on either sideimmediately over the bottom row of contacts are offered by the slotretention system to secure the SIMM in the slot. Although it maynot be visible in the reproduction, the peak SIMM provides gold contactsand also the bottom SIMM tin contacts.Figure 5-1. 72-pin SIMM (top) and 30-pin SIMMDIMM (Dual Inline Memory Module)DIMMs are dual-side modules that use connectors on both sides of thecircuit board. SDR-SDRAM DIMMs have 168 pins, yet SDR-SDRAM is alsoaccessible in 100- and 144-pin DIMMs. DDR-SDRAM is packaged in 184-pinDIMMs, which are physically equivalent to typical 168-pin SDR-SDRAMDIMMs, but have actually added pins and various keying notch positionsto proccasion them from being interadjusted. DDR-II DIMMs are similar toDDR DIMMs, yet use a 232-pin connector. Only SDR-SDRAM, DDR-SDRAM,and also EDO are typically packaged as DIMMs.SODIMM (Small Rundown DIMM)A one-of-a-kind package offered in notebook computer systems and also on some videoadapters.RIMMA Rambus RDRAM module.RIMM is a profession name quite than an acronym. RIMMs are physicallycomparable to conventional SDRAM DIMMs, except that the keying notches arein different areas. RDRAM is available in 168-pin and also 184-pinmodules. Early RDRAM motherboards used 168-pin RIMMs. Most currentRDRAM motherboards usage 184-pin RIMMs.Figure 5-2 shows the 2 a lot of prevalent physicalpackages for memory used in recent systems. The height module is a168-pin PC133 SDRAM DIMM. The bottom module is a 184-pin PC2100DDR-SDRAM DIMM (faster DDR-SDRAM modules use the very same package). Thephysical dimensions of both are the same: 5.375 inches (13.6525 cm)wide by 1.375 inches (3.4925 cm) tall. The width is standardized forall memory modules to ensure they fit the typical slot. The heightmight vary slightly, and is a factor just in that tall modules mayinterfere through other components in a tightly packed mechanism. Both ofthese modules use nine chips, which shows that they are ErrorChecking and Correction (ECC) modules. Nonparity modules use onlyeight chips.Figure 5-2. PC133 SDRAM DIMM (top) and PC2100 DDR-SDRAM DIMMThe significant distinction between these DIMMs, various other than the number ofpins, is the location of the keying notches. SDRAM DIMMs use twonotches, one centered and also one counter. DDR-SDRAM DIMMs usage only onecounter keying notch. The number and also place of these keying notchesensure that only the proper memory type deserve to be mounted in a slotand that the module is oriented effectively. Rambus RIMMs use similarphysical packaging, yet through the keying notches in differentplaces. Rambus RIMMs likewise cover the individual chips through a metalshroud designed to dissipate warm.5.4.1 Banks versus RowsMemory rowsand also financial institutions are conveniently confused. Rows are physicalteams and financial institutions are logical groups. A financial institution comprises one or morerows, the number relying on CPU attend to bus width and also the width ofthe memory, which is very closely associated with its create element.DIPThese are 1 little bit wide, and also require eight chips per row (nine, ifparity is used). The number of rows per bank depends on the CPU.XT-class PCs, which use an 8-little memory bus, need one row perfinancial institution. 286s (16-little bit bus) call for two rows per financial institution. 386s and also 486s(32-bit bus) call for 4 rows per bank.30-pin SIMM These are 8 bits wide. 286s require two modules (rows) per bank. 386sand 486s need four modules per bank. Pentiums (64-bit bus) requireeight modules per bank.72-pin SIMMs These are 32 bits wide. 486s call for one module per bank. Pentium andgreater devices require 2 modules per bank.168-pin and also 184-pin DIMMsThese are 64 bits wide. One DIMM always creates one financial institution.168-pin and 184-pin RIMMsOlder motherboards usage 168-pin RIMMs. Many more recent motherboards use184-pin RIMMs. Although most RIMMs technically usage a 16- or 18-bitinteractions channel, a solitary RIMM appears to the chipset as onebank. Some motherboards have a single RDRAM channel, such as thosebased on the Intel 820 chipset, and permit RIMMs to be installedindividually. Other motherboards, such as those based upon the Intel850 chipcollection, have dual RDRAM channels, and call for that RIMMs bemounted in pairs, one per channel. Keep in mind, but, that a 32/36-bitRIMM is physically packaged as one module, yet is logically twoRIMMs. That means you deserve to populate a dual-channel Rambus motherboardthrough simply one 32/36-little RIMM.

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In a RIMM-based device, all memory slots must be occupied, eitherthrough a RIMM module or with a Continuity RIMM(CRIMM), which offers electric continuity.If any type of RIMM slot is empty, the device will not boot. For those whojob-related mostly with DIMMs, as we carry out, it"s straightforward toforacquire this necessity. We spent an hour one day trying to figureout why a mechanism we"d constructed simply sat tright here beepingrather of booting. Turned out that we"d forgottento install the CRIMM, which was buried deep in the motherboardpackaging. All RDRAM motherboards we know of enable RIMMs and also CRIMMsto be installed interchangeably. That is, it doesn"tissue which slots you populate via RIMMs and also which with CRIMMs.
You have to install memory at least one fullbank at a time. If you install even more than one bank, you must installin full-bank increments. One 168-pin or 184-pin DIMM or 16/18-bitRIMM always amounts to one financial institution, regardless of the form of motherboard orprocessor. One 72-pin SIMM amounts to one bank in 386s and 486s. TwoSIMMs equal one financial institution in Pentiums. Older units, specifically 486s,may interleave financial institutions to boost performance, which requiresinstalling 2 banks at a time.
Motherboards through dual-channel DDR-SDRAM memory controllers, such asthe Intel D875PBZ or the ASUS A7N8X Deluxe, call for including DIMMs inpairs to allow dual-channel operation. Most such motherboards canrun via only one DIMM installed, yet that disables dual-channelmemory operation, which may incur a far-ranging performance penalty.When installing DIMMs in pairs, the ideal exercise is to use onlythe same DIMMs, but some motherboards permit making use of DIMMs with mixedspeeds. See the motherboard hand-operated for complete details.
Inenhancement to financial institutions, you may should think about rowsor tools, particularly if you install a largeamount of memory. Each SDRAM chipset supports at many a provided numberof rows of memory, and this limit does not necessarily correspondwith the number of physical memory slots on a motherboard that usesthat chipset. A single-sided SDRAM DIMM haschips physically installed on only one side of the module, andappears to the chipcollection as one row of memory. A double-sidedSDRAM DIMM has chips physically mounted on both sides ofthe module, and appears to the chipset as two rows of memory.So, for instance, if a motherboard has actually 3 physical DIMM slotsand its chipcollection supports just four rows of memory, you are restrictedin terms of which DIMMs you have the right to install. You can install single-sidedDIMMs in all three memory slots bereason those 3 DIMMs complete only3 rows. You can install one double-sided DIMM and also twosingle-sided DIMMs because that totals only four rows. But if youinstall 2 double-sided DIMMs, you have to leave the 3rd slot emptybereason the two double-sided DIMMs complete four rows, which is themaximum the chipcollection supports.Two other factors mayhave a bearing on how many type of SDRAM DIMMs you have the right to install:Memory speedInstalling quicker memory may mitigate the variety of DIMMs you caninstall. For instance, a motherboard might have actually three DIMM slots, all ofwhich have the right to be populated with PC2700 DIMMs. But that motherboard maysupport at a lot of two PC3200 DIMMs, forcing you to leave the 3rd DIMMslot empty if you install PC3200 memory.
Using too much rapid memory have the right to cause subtle memory troubles.Motherboard, device, and also memory manufacturers frequently execute not publicizethis difficulty. As a rule of thumb once installing rapid memory, choosefewer high-capacity modules in preference to more lower-capacitymodules. This trouble is especially likely to aincrease when you"push the envelope"?forexample, by installing PC3200 or PC3500 memory, overclocking yourmechanism, or running dual processors.
Unbuffered versus Registered DIMMsUnbuffered SDRAM DIMMs call for the chipsetmemory controller to regulate each chip on the DIMM individually. Thereis an upper limit on exactly how many kind of memory chips the memory controller cancontrol, which restricts the total number of unbuffered memory chipsthat the motherboard have the right to assistance. Registered SDRAMDIMMs (sometimes dubbed Buffered SDRAMDIMMs) put a second layer of circuitry in between thechipcollection memory controller and the actual memory chips, which ineffect reduces the number of memory chips visible to the chipsetmemory controller to a controlled number. Registered DIMMs areuncommon in desktop units because they cost more and also are slowerthan unbuffered DIMMs. A CL2 registered DIMM has around the samememory performance as a CL3 unbuffered DIMM. Some motherboardsassistance just unbuffered DIMMs, others just registered DIMMs, and also somesupport either type. A motherboard that supports either type mayallow using one or the various other, however not both at when.RDRAM units also limit the variety of memory chips that can beset up at one time. Each RIMM comprises multiple RDRAM memorychips, each of which is referred to as an RDRAM tool.A typical RDRAM chipset might assistance at a lot of 32 RDRAM devices perchannel. If a RIMM supplies 16 RDRAM chips (devices), you can installtwo of those RIMMs on the channel and also still be within the top limiton RDRAM gadgets. Attempting to install a third RIMM on that systemwould cause the mechanism to fail to boot. Conversely, if you wereinstalling RIMMs that use eight gadgets, 3 RIMMs would certainly total only24 devices, and also so would certainly be within the device limitation of thatchannel.5.4.2 Chip DensityMemory modules are created fromindividual memory chips, which differ in their capacity. Chipcapacities are specified in megabits (Mb or Mbit) fairly thanmegabytes (MB). Because there are eight bits per byte, a memorymodule that provides eight chips deserve to keep the variety of megabytesmentioned by the megalittle dimension of the chip. For instance, a memorymodule that supplies eight 128-Mlittle bit chips is a 128 MB memory module.Recent memory modules may use 16-, 64-, 128-, 256-, or 512-Mbitchips. A memory module of a specified capacity might usage fewerhigh-capacity chips or even more low-capacity chips. For instance, a 256 MBDIMM can usage eight 256-Mbit chips or sixteen 128-Mlittle chips.Although both DIMMs have the exact same 256 MB capacity, the eight-chipDIMM is a single-sided DIMM and the 16-chip DIMM is a double-sidedDIMM. For a provided capacity, it"s primarily better toinstall a single-sided DIMM when possible bereason chipsets supportjust so many rows of memory, and a double-sided DIMM"offers up" 2 rows.However before, you need to not install memory that offers higher-capacity chipsthan your chipcollection supports. For example, the Intel 815 chipsetsupports 16-, 64-, 128-, and also 256-Mlittle chips, so an 815-basedmotherboard could usage either the eight-chip or the 16-chip, 256 MBDIMM. The Intel 440BX chipcollection, yet, supports just 16-, 64-, and128-Mbit chips, so a 440BX-based motherboard might use only the16-chip 256 MB DIMM. Attempting to install a DIMM that useshigher-capacity chips than the chipset supports has actually unpredictableresults. Sometimes, the system will certainly sindicate refusage to recognizethe DIMM. Other times, the system will certainly recognize the DIMM, but atsome fractivity (generally one-half or one-quarter) of its actualcapacity.You need to additionally protect against using chips of also low a capacity. For instance,the Intel 875P chipset supports 128-, 256-, and 512-Mlittle bit chips, butnot 64-Mlittle bit chips. Installing an older DIMM that offers 64-Mlittle bit chipsin an Intel 875P-based motherboard results in the DIMM not beingknown.
If you usage Crucial memory, which we recommend, the best method to makecertain that the module you choose is compatible with your device is tousage the Crucial Memory Selector on the Crucial house page (http://www.vital.com/). That tool allowsyou to specify your device or motherboard version, and also display screens onlymemory modules that are compatible through your mechanism.

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5.4.3 Parity and also ECC Memory Two kinds of memory use extra bits tosave checkamount indevelopment that deserve to detect and also periodically correctmemory errors. They are as follows:Parity memoryUses nine bits per byte to administer basic error detection, so simpleregarding be usemuch less on contemporary Computers. Many early on DIP-based PCs requiredparity memory, and also so offered nine chips per row. SIMMs, which are muchmore reputable than DIPs, made parity unimportant. The Intel TritonPentium-class chipcollection and completing chipsets removed support forparity memory. Recent chipsets again assistance parity memory, but thereis no excellent factor to use it.Although parity memory is still sold, buy it just if your computerneeds it. Some computer systems perform not allow mixing parity and also nonparitymodules. Before buying parity memory, verify which kind is alreadyset up and whether your chipset have the right to mix parity via nonparitymemory. Identify parity modules by counting the chips on the module.If that number is evenly divisible by 3, it"s aparity module. If nonparity memory is mounted, or if parity memoryis mounted yet your chipcollection allows mixing kinds, buy nonparitymemory. Buy parity memory only if parity memory is already presentand also your chipset does not allow mixing kinds.ECC memory An magnified develop of error-checking memorythat deserve to detect single- and also multibit errors and also correct all single-and some multibit errors. ECC originated on mainframes, moved tominicomputers, and also is now prevalent on COMPUTER servers.ECC memory calls for 5 extra bits to safeguard an 8-little byte, 6 toprotect a 16-little bit word, seven to protect a 32-bit word, and also eight toprotect a 64-bit word. A 72-bit-wide DIMM supports either parity orECC interchangeably. Chipsets that assistance 168-pin DIMMs might alsoassistance ECC, although ECC is not always applied in BIOS. If yourBIOS supports it, you have the right to use ECC by installing 72-little DIMMs andpermitting ECC in Chipcollection Setup. The downside, yet, is that 72-bitDIMMs expense around 12.5% more than typical 64-little bit DIMMs, and enablingECC reduces memory performance, frequently by about 3%. Use ECC memoryon servers when continuous uptime is critical. Do not use ECC memory intraditional desktop computer PCs except those that have actually a large amount of memoryinstalled.
One common reason of "flipped bit"memory errors is, believe it or not, cosmic rays. The even more memory youhave actually installed, the even more likely it is that a random cosmic ray willinfluence one of the memory cells in a chip on your mechanism, leading to thecontents of that cell to flip from a binary zero to a one or viceversa. We do not pretfinish to understand this problem,yet we"ve been told by memory experts that forsystems via 512 MB of RAM using ECC versus nonparity memory is aboutan even trade-off in regards to added cost and shed performance versusthe likelihood of memory errors. For devices with 768+ MB, we usage ECCmemory exclusively, if the motherboard supports it.
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