Memory isavailable in assorted physical packaging. Around in bespeak of theirappearance, the major types of dram packaging include:DIP (Dual Inline pin Package) This package comprises arectangular chip v a row of pins under each long side, make itresemble an insect. DIP was the most typical DRAM package used in PCsthrough early 386 models. Dive chips were produced in Page mode andFast page Mode, and are long obsolete. Dip packaging was likewise usedfor L2 cache memory on most 486 and also some Pentium-class motherboards.DIP dram is useless nowadays.SIPP (Single Inline pin Package)This package turns a dive chip ~ above its side and also extends all leadsstraight out one side, parallel to the airplane of the chip. SIPPs wereintended to permit memory to be installed an ext densely, and also were usedin a couple of 386SX systems, yet they never captured on. SIPPs were producedin web page Mode and also Fast Page mode form, and also are long obsolete.SIMM (Single Inline memory Module)This package mounts multiple individual DRAM dive chips ~ above a smallcircuit board with a card-edge connector designed come fit a socket onthe motherboard. Mainstream SIMMs have been manufactured in 2 formfactors:30-pinThese SIMMs were offered in a few 286systems, many 386 systems, and some 486 systems, and also were developed inPage Mode and also Fast Page setting form. Return they are still available,30-pin SIMMs room obsolete. If girlfriend tear down an old system, any kind of 30-pinSIMMs friend salvage are too small and too slow to it is in useful. However,some laser printers do use them.72-pinThese SIMMs were used in part 386 systems,most 486 systems, and virtually all Pentium-class systems built beforethe arrival of DIMMs. 72-pin SIMMs were created in rapid Page Mode,EDO form, and BEDO form. When tearing down old systems, 72-pin SIMMsmay be precious salvaging, together they have the right to be supplied to increase the storage on alate-model Pentium or Pentium Pro mechanism or to expand the storage insome laser printers.Figure 5-1 mirrors a 72-pin SIMM (top) and a 30-pinSIMM. The 72-pin SIMM is keyed through the notch at the bottom right; the30-pin SIMM through the notch in ~ the bottom left. The holes on one of two people sideimmediately over the bottom heat of contact are used by the slotretention device to secure the SIMM in the slot. Although it maynot be visible in the reproduction, the height SIMM provides gold contactsand the bottom SIMM believe contacts.Figure 5-1. 72-pin SIMM (top) and also 30-pin SIMMDIMM (Dual Inline memory Module)DIMMs room dual-side modules that use connectors on both sides of thecircuit board. SDR-SDRAM DIMMs have actually 168 pins, yet SDR-SDRAM is alsoavailable in 100- and 144-pin DIMMs. DDR-SDRAM is packaged in 184-pinDIMMs, which room physically comparable to typical 168-pin SDR-SDRAMDIMMs, but have extr pins and different keying notch positionsto avoid them from gift interchanged. DDR-II DIMMs are similar toDDR DIMMs, yet use a 232-pin connector. Just SDR-SDRAM, DDR-SDRAM,and EDO are frequently packaged together DIMMs.SODIMM (Small overview DIMM)A unique package used in notebook computers and also on some videoadapters.RIMMA Rambus RDRAM module.RIMM is a profession name quite than an acronym. RIMMs are physicallysimilar to conventional SDRAM DIMMs, other than that the keying notches arein different locations. RDRAM is accessible in 168-pin and also 184-pinmodules. Early on RDRAM motherboards used 168-pin RIMMs. Many currentRDRAM motherboards usage 184-pin RIMMs.Figure 5-2 shows the two most typical physicalpackages because that memory offered in recent systems. The top module is a168-pin PC133 SDRAM DIMM. The bottom module is a 184-pin PC2100DDR-SDRAM DIMM (faster DDR-SDRAM modules usage the same package). Thephysical dimensions of both space the same: 5.375 inches (13.6525 cm)wide by 1.375 customs (3.4925 cm) tall. The broad is standardization forall storage modules come ensure lock fit the conventional slot. The heightmay differ slightly, and also is a element only in that tall modules mayinterfere through other components in a tightly packed system. Both ofthese modules usage nine chips, which suggests that they room ErrorChecking and Correction (ECC) modules. Nonparity modules usage onlyeight chips.Figure 5-2. PC133 SDRAM DIMM (top) and PC2100 DDR-SDRAM DIMMThe significant difference in between these DIMMs, various other than the number ofpins, is the location of the keying notches. SDRAM DIMMs usage twonotches, one centered and one offset. DDR-SDRAM DIMMs use only oneoffset keying notch. The number and also position of this keying notchesensure that only the proper memory type can be mounted in a slotand that the module is oriented correctly. Rambus RIMMs usage similarphysical packaging, however with the keying notches in differentlocations. Rambus RIMMs likewise cover the separation, personal, instance chips through a metalshroud designed to dissipate heat.5.4.1 financial institutions versus RowsMemory rowsand financial institutions are quickly confused. Rows are physicalgroups and banks space logical groups. A financial institution comprises one or morerows, the number depending upon CPU address bus width and the broad ofthe memory, which is closely associated with its kind factor.DIPThese space 1 little bit wide, and require eight chips per heat (nine, ifparity is used). The number of rows per financial institution depends on the CPU.XT-class PCs, which usage an 8-bit storage bus, need one heat perbank. 286s (16-bit bus) need two rows every bank. 386s and also 486s(32-bit bus) require four rows every bank.30-pin SIMM These are 8 bits wide. 286s need two modules (rows) every bank. 386sand 486s require four modules every bank. Pentiums (64-bit bus) requireeight modules per bank.72-pin SIMMs These room 32 bits wide. 486s call for one module every bank. Pentium andhigher systems need two modules per bank.168-pin and also 184-pin DIMMsThese space 64 bits wide. One DIMM constantly forms one bank.168-pin and 184-pin RIMMsOlder motherboards usage 168-pin RIMMs. Most newer motherboards use184-pin RIMMs. Although most RIMMs technically usage a 16- or 18-bitcommunications channel, a solitary RIMM shows up to the chipset together onebank. Some motherboards have actually a solitary RDRAM channel, such together thosebased on the Intel 820 chipset, and enable RIMMs to it is in installedindividually. Various other motherboards, such as those based on the Intel850 chipset, have dual RDRAM channels, and also require the RIMMs beinstalled in pairs, one every channel. Note, however, the a 32/36-bitRIMM is physical packaged as one module, but is logically twoRIMMs. That way you deserve to populate a dual-channel Rambus motherboardwith just one 32/36-bit RIMM.

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In a RIMM-based system, all storage slots need to be populated, eitherwith a RIMM module or through a continuous RIMM(CRIMM), i m sorry provides electric continuity.If any type of RIMM slot is empty, the mechanism will not boot. For those whowork primarily with DIMMs, as we do, it"s easy toforget this requirement. We spent an hour someday trying to figureout why a system we"d developed just sat there beepinginstead the booting. Turned the end that we"d forgottento download the CRIMM, i m sorry was buried deep in the motherboardpackaging. All RDRAM motherboards we know of allow RIMMs and also CRIMMsto be set up interchangeably. The is, that doesn"tmatter which slots you populate through RIMMs and which through CRIMMs.
You should install memory at the very least one fullbank at a time. If friend install more than one bank, you must installin full-bank increments. One 168-pin or 184-pin DIMM or 16/18-bitRIMM always equals one bank, nevertheless of the type of motherboard orprocessor. One 72-pin SIMM equals one financial institution in 386s and also 486s. TwoSIMMs same one financial institution in Pentiums. Older systems, an especially 486s,may interleave financial institutions to enhance performance, i beg your pardon requiresinstalling two banks at a time.
Motherboards with dual-channel DDR-SDRAM memory controllers, together asthe Intel D875PBZ or the ASUS A7N8X Deluxe, require including DIMMs inpairs to allow dual-channel operation. Many such motherboards canoperate with only one DIMM installed, yet that disables dual-channelmemory operation, which might incur a far-ranging performance penalty.When installing DIMMs in pairs, the finest practice is to use onlyidentical DIMMs, however some motherboards allow using DIMMs with mixedspeeds. Check out the motherboard hand-operated for complete details.
Inaddition come banks, you may need to take into consideration rowsor devices, an especially if you install a largeamount of memory. Every SDRAM chipset support at most a offered numberof rows the memory, and this limit does not necessarily correspondwith the variety of physical memory slot on a motherboard the usesthat chipset. A single-sided SDRAM DIMM haschips physically mounted on just one side of the module, andappears come the chipset as one heat of memory. A double-sidedSDRAM DIMM has actually chips physically set up on both political parties ofthe module, and also appears come the chipset as two rows the memory.So, because that example, if a motherboard has actually three physical DIMM slotsand that chipset supports only 4 rows of memory, you space restrictedin terms of which DIMMs you can install. You have the right to install single-sidedDIMMs in all three memory slots due to the fact that those three DIMMs complete onlythree rows. You deserve to install one double-sided DIMM and twosingle-sided DIMMs due to the fact that that totals only four rows. However if youinstall two double-sided DIMMs, you need to leave the 3rd slot emptybecause the 2 double-sided DIMMs total four rows, i m sorry is themaximum the chipset supports.Two other determinants mayhave a bearing on how many SDRAM DIMMs you have the right to install:Memory speedInstalling faster memory may reduce the variety of DIMMs girlfriend caninstall. Because that example, a motherboard may have three DIMM slots, all ofwhich have the right to be lived in with PC2700 DIMMs. However that motherboard maysupport at most two PC3200 DIMMs, forcing girlfriend to leaving the third DIMMslot empty if you download PC3200 memory.
Using also much rapid memory can cause subtle storage problems.Motherboard, system, and also memory manufacturers regularly do not publicizethis problem. Together a ascendancy of thumb when installing quick memory, choosefewer high-capacity modules in choice to an ext lower-capacitymodules. This trouble is an especially likely to arise as soon as you"push the envelope"?forexample, by installation PC3200 or PC3500 memory, overclocking yoursystem, or running dual processors.
Unbuffered matches Registered DIMMsUnbuffered SDRAM DIMMs need the chipsetmemory controller to manage each chip top top the DIMM individually. Thereis an upper limit top top how countless memory chips the storage controller canmanage, i m sorry restricts the total number of unbuffered storage chipsthat the motherboard can support. Registered SDRAMDIMMs (sometimes called Buffered SDRAMDIMMs) put an additional layer the circuitry in between thechipset memory controller and also the actual storage chips, i m sorry ineffect reduce the variety of memory chips clearly shows to the chipsetmemory controller come a controlled number. Registered DIMMs areuncommon in desktop computer systems because they cost an ext and are slowerthan unbuffered DIMMs. A CL2 registered DIMM has about the samememory performance as a CL3 unbuffered DIMM. Some motherboardssupport just unbuffered DIMMs, others just registered DIMMs, and also somesupport either sort. A motherboard that supports either type mayallow using one or the other, however not both at once.RDRAM systems also limit the number of memory chips that have the right to beinstalled in ~ one time. Every RIMM comprises lot of RDRAM memorychips, every of i beg your pardon is called an RDRAM device.A typical RDRAM chipset might support at many 32 RDRAM tools perchannel. If a RIMM provides 16 RDRAM chips (devices), you could installtwo of those RIMMs on the channel and also still be within the top limiton RDRAM devices. Attempting to download a third RIMM on the systemwould cause the system to fail to boot. Vice versa, if friend wereinstalling RIMMs that use eight devices, 3 RIMMs would complete only24 devices, and so would certainly be within the maker limitation that thatchannel.5.4.2 Chip DensityMemory modules are created fromindividual storage chips, which vary in their capacity. Chipcapacities room specified in megabits (Mb or Mbit) quite thanmegabytes (MB). Due to the fact that there are eight bits per byte, a memorymodule that supplies eight chips have the right to store the variety of megabytesspecified by the megabit dimension of the chip. Because that example, a memorymodule that provides eight 128-Mbit chips is a 128 MB memory module.Recent storage modules might use 16-, 64-, 128-, 256-, or 512-Mbitchips. A memory module of a specified capacity might use fewerhigh-capacity chips or more low-capacity chips. For example, a 256 MBDIMM can use eight 256-Mbit chips or sixteen 128-Mbit chips.Although both DIMMs have actually the exact same 256 MB capacity, the eight-chipDIMM is a single-sided DIMM and also the 16-chip DIMM is a double-sidedDIMM. For a provided capacity, it"s generally much better toinstall a single-sided DIMM when feasible because chipsets supportonly so plenty of rows of memory, and also a double-sided DIMM"uses up" two rows.However, you must not install storage that offers higher-capacity chipsthan your chipset supports. For example, the Intel 815 chipsetsupports 16-, 64-, 128-, and 256-Mbit chips, therefore an 815-basedmotherboard might use either the eight-chip or the 16-chip, 256 MBDIMM. The Intel 440BX chipset, however, supports only 16-, 64-, and128-Mbit chips, for this reason a 440BX-based motherboard can use just the16-chip 256 MB DIMM. Attempting to download a DIMM the useshigher-capacity chips 보다 the chipset supports has unpredictableconsequences. Sometimes, the system will simply refuse to recognizethe DIMM. Other times, the system will identify the DIMM, however atsome portion (typically one-half or one-quarter) of its actualcapacity.You must additionally avoid utilizing chips of also low a capacity. Because that example,the Intel 875P chipset support 128-, 256-, and also 512-Mbit chips, butnot 64-Mbit chips. Installation an larger DIMM that supplies 64-Mbit chipsin an Intel 875P-based motherboard outcomes in the DIMM no beingrecognized.
If you use vital memory, which us recommend, the best way to makesure the the module you select is compatible with your mechanism is touse the an essential Memory Selector ~ above the critical home page ( That device allowsyou come specify your system or motherboard model, and also displays onlymemory modules that room compatible v your system.

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5.4.3 Parity and ECC storage Two types of memory usage extra bits tostore checksum info that can detect and also sometimes correctmemory errors. They space as follows:Parity memoryUses ripe bits every byte come provide straightforward error detection, so simpleas to be useless on modern PCs. Most early on DIP-based computers requiredparity memory, and so provided nine chips every row. SIMMs, which are muchmore reputable than DIPs, made parity unnecessary. The Intel TritonPentium-class chipset and also competing chipsets eliminated support forparity memory. Recent chipsets again assistance parity memory, but thereis no good reason to use it.Although parity storage is tho sold, purchase it only if her computerrequires it. Some computers do not enable mixing parity and also nonparitymodules. Before buying parity memory, verify which type is alreadyinstalled and also whether her chipset can mix parity with nonparitymemory. Determine parity modules by count the chips on the module.If that number is evenly divisible by three, it"s aparity module. If nonparity memory is installed, or if same memoryis installed however your chipset allows mixing types, purchase nonparitymemory. Buy parity memory just if parity memory is already presentand her chipset go not enable mixing types.ECC memory one enhanced form of error-checking memorythat can detect single- and multibit errors and also correct every single-and part multibit errors. ECC originated on mainframes, moved tominicomputers, and also is now common on pc servers.ECC storage requires 5 extra bits to protect an 8-bit byte, 6 toprotect a 16-bit word, seven to defend a 32-bit word, and eight toprotect a 64-bit word. A 72-bit-wide DIMM supports one of two people parity orECC interchangeably. Chipsets that support 168-pin DIMMs may alsosupport ECC, although ECC is not constantly implemented in BIOS. If yourBIOS supports it, you deserve to use ECC by installation 72-bit DIMMs andenabling ECC in Chipset Setup. The downside, however, is that 72-bitDIMMs cost around 12.5% an ext than traditional 64-bit DIMMs, and also enablingECC reduces storage performance, typically by around 3%. Usage ECC memoryon servers when continuous uptime is critical. Execute not use ECC memory instandard desktop PCs other than those that have actually a huge amount the memoryinstalled.
One common reason of "flipped bit"memory errors is, think it or not, cosmic rays. The an ext memory youhave installed, the an ext likely that is the a arbitrarily cosmic beam willimpact among the memory cells in a chip on your system, resulting in thecontents of that cell to upper and lower reversal from a binary zero to a one or viceversa. Us don"t ~ do so to know this issue,but we"ve to be told by memory specialists that forsystems with 512 MB the RAM using ECC matches nonparity storage is aboutan also trade-off in terms of extra cost and also lost power versusthe likelihood of memory errors. For solution with 768+ MB, we usage ECCmemory exclusively, if the motherboard support it.