Memory isavailable in various physical packaging. Around in order of theirappearance, the major types of dram packaging include:DIP (Dual Inline pen Package) This package comprises arectangular chip with a row of pins under each lengthy side, making itresemble one insect. DIP was the most typical DRAM package provided in PCsthrough early on 386 models. Dive chips were created in Page mode andFast web page Mode, and also are lengthy obsolete. Dive packaging was likewise usedfor L2 cache storage on many 486 and also some Pentium-class motherboards.DIP theatre is useless nowadays.SIPP (Single Inline pen Package)This package transforms a emboldened chip on its side and extends every leadsstraight the end one side, parallel to the plane of the chip. SIPPs wereintended to allow memory to be installed more densely, and were usedin a few 386SX systems, however they never captured on. SIPPs were producedin page Mode and Fast Page mode form, and also are long obsolete.SIMM (Single Inline storage Module)This parcel mounts multiple separation, personal, instance DRAM emboldened chips top top a smallcircuit board through a card-edge connector designed come fit a socket onthe motherboard. Tendency SIMMs have actually been manufactured in two formfactors:30-pinThese SIMMs were supplied in a few 286systems, many 386 systems, and also some 486 systems, and were created inPage Mode and also Fast Page setting form. Although they space still available,30-pin SIMMs are obsolete. If friend tear under an old system, any kind of 30-pinSIMMs you salvage room too tiny and too sluggish to it is in useful. However,some laser printers perform use them.72-pinThese SIMMs were used in some 386 systems,most 486 systems, and virtually all Pentium-class systems built beforethe introduction of DIMMs. 72-pin SIMMs were developed in rapid Page Mode,EDO form, and also BEDO form. As soon as tearing down old systems, 72-pin SIMMsmay be precious salvaging, as they deserve to be used to increase the memory on alate-model Pentium or Pentium Pro system or to increase the storage insome laser printers.Figure 5-1 mirrors a 72-pin SIMM (top) and a 30-pinSIMM. The 72-pin SIMM is keyed by the notch in ~ the bottom right; the30-pin SIMM by the notch at the bottom left. The holes on one of two people sideimmediately above the bottom row of contacts are provided by the slotretention device to for sure the SIMM in the slot. Although the maynot be clearly shows in the reproduction, the optimal 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 top top both sides of thecircuit board. SDR-SDRAM DIMMs have actually 168 pins, but SDR-SDRAM is alsoavailable in 100- and also 144-pin DIMMs. DDR-SDRAM is packaged in 184-pinDIMMs, which space physically comparable to typical 168-pin SDR-SDRAMDIMMs, but have additional pins and also different keying notch positionsto protect against them from being interchanged. DDR-II DIMMs are comparable toDDR DIMMs, yet use a 232-pin connector. Just SDR-SDRAM, DDR-SDRAM,and EDO are typically packaged together DIMMs.SODIMM (Small summary DIMM)A special package provided in notebook computers and on part videoadapters.RIMMA Rambus RDRAM module.RIMM is a trade name fairly than an acronym. RIMMs room physicallysimilar to typical SDRAM DIMMs, other than that the keying notches arein different locations. RDRAM is available in 168-pin and 184-pinmodules. Early RDRAM motherboards supplied 168-pin RIMMs. Many currentRDRAM motherboards use 184-pin RIMMs.Figure 5-2 mirrors the two most common physicalpackages for memory provided 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 very same package). Thephysical dimensions of both are the same: 5.375 inches (13.6525 cm)wide by 1.375 customs (3.4925 cm) tall. The width is standardized forall memory modules come ensure they fit the traditional slot. The heightmay vary slightly, and also is a factor only in that tall modules mayinterfere with other contents in a tightly pack system. Both ofthese modules usage nine chips, which suggests that they room ErrorChecking and also Correction (ECC) modules. Nonparity modules usage onlyeight chips.Figure 5-2. PC133 SDRAM DIMM (top) and also PC2100 DDR-SDRAM DIMMThe major difference in between these DIMMs, various other than the number ofpins, is the ar of the keying notches. SDRAM DIMMs usage twonotches, one centered and one offset. DDR-SDRAM DIMMs use only oneoffset keying notch. The number and position of this keying notchesensure that only the appropriate memory kind can be mounted in a slotand the the module is oriented correctly. Rambus RIMMs use similarphysical packaging, but with the keying notches in differentlocations. Rambus RIMMs additionally cover the separation, personal, instance chips through a metalshroud designed to dissipate heat.5.4.1 banks versus RowsMemory rowsand financial institutions are conveniently confused. Rows are physicalgroups and banks are logical groups. A financial institution comprises one or morerows, the number depending upon CPU address bus width and also the width ofthe memory, which is closely linked with its kind factor.DIPThese room 1 little wide, and require eight chips per row (nine, ifparity is used). The number of rows per financial institution depends on the CPU.XT-class PCs, which use an 8-bit memory bus, require one row perbank. 286s (16-bit bus) need two rows per bank. 386s and 486s(32-bit bus) require four rows per bank.30-pin SIMM These room 8 bits wide. 286s call for two modules (rows) per bank. 386sand 486s require 4 modules every bank. Pentiums (64-bit bus) requireeight modules per bank.72-pin SIMMs These room 32 bits wide. 486s need one module per bank. Pentium andhigher systems call for two modules per bank.168-pin and also 184-pin DIMMsThese room 64 bits wide. One DIMM always forms one bank.168-pin and also 184-pin RIMMsOlder motherboards usage 168-pin RIMMs. Many newer motherboards use184-pin RIMMs. Although most RIMMs technically usage a 16- or 18-bitcommunications channel, a single RIMM shows up to the chipset together onebank. Part motherboards have actually a solitary RDRAM channel, such as thosebased ~ above the Intel 820 chipset, and allow RIMMs to be installedindividually. Other motherboards, such as those based on the Intel850 chipset, have twin RDRAM channels, and require the RIMMs beinstalled in pairs, one every channel. Note, however, the a 32/36-bitRIMM is physically packaged as one module, but is logically twoRIMMs. That means you have the right to populate a dual-channel Rambus motherboardwith simply one 32/36-bit RIMM.

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In a RIMM-based system, all memory slots should be populated, eitherwith a RIMM module or with a continuous RIMM(CRIMM), i beg your pardon provides electrical continuity.If any RIMM slot is empty, the system will no boot. For those whowork mainly with DIMMs, together we do, it"s basic toforget this requirement. We invested an hour someday trying to figureout why a mechanism we"d built just satellite there beepinginstead of booting. Turned out that we"d forgottento install the CRIMM, i beg your pardon was buried deep in the motherboardpackaging. All RDRAM motherboards we know of enable RIMMs and also CRIMMsto be mounted interchangeably. The is, the doesn"tmatter which slot you populate v RIMMs and also which through CRIMMs.
You need to 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, regardless of the type of motherboard orprocessor. One 72-pin SIMM equals one bank in 386s and 486s. TwoSIMMs same one financial institution in Pentiums. Older systems, specifically 486s,may interleave financial institutions to improve performance, i m sorry requiresinstalling two banks at a time.
Motherboards v dual-channel DDR-SDRAM memory controllers, such asthe Intel D875PBZ or the ASUS A7N8X Deluxe, require including DIMMs inpairs to allow dual-channel operation. Many such motherboards canoperate with just one DIMM installed, but that disables dual-channelmemory operation, which may incur a far-ranging performance penalty.When installation DIMMs in pairs, the best practice is to use onlyidentical DIMMs, however some motherboards enable using DIMMs through mixedspeeds. Watch the motherboard hands-on for finish details.
Inaddition to banks, you may need to take into consideration rowsor devices, an especially if you install a largeamount the memory. Every SDRAM chipset supports at most a provided numberof rows of memory, and this limit does not necessarily correspondwith the variety of physical memory slots on a motherboard that usesthat chipset. A single-sided SDRAM DIMM haschips physically mounted on just one next of the module, andappears to the chipset as one row of memory. A double-sidedSDRAM DIMM has actually chips physically set up on both political parties ofthe module, and also appears to the chipset as two rows of memory.So, for example, if a motherboard has actually three physical DIMM slotsand that is chipset supports only 4 rows of memory, you are restrictedin regards to which DIMMs you can install. You have the right to install single-sidedDIMMs in all 3 memory slots due to the fact that those 3 DIMMs full onlythree rows. You deserve to install one double-sided DIMM and also twosingle-sided DIMMs since that totals only four rows. However if youinstall 2 double-sided DIMMs, you should leave the 3rd slot emptybecause the 2 double-sided DIMMs complete four rows, i beg your pardon is themaximum the chipset supports.Two other components mayhave a bearing top top how plenty of SDRAM DIMMs you have the right to install:Memory speedInstalling quicker memory may reduce the number of DIMMs friend caninstall. Because that example, a motherboard may have actually three DIMM slots, all ofwhich have the right to be occupied with PC2700 DIMMs. Yet that motherboard maysupport at many two PC3200 DIMMs, forcing friend to leaving the third DIMMslot empty if you download PC3200 memory.
Using too much fast memory can cause subtle memory problems.Motherboard, system, and also memory manufacturers often do no publicizethis problem. As a ascendancy of thumb once installing rapid memory, choosefewer high-capacity modules in choice to much more lower-capacitymodules. This difficulty is specifically likely come arise once you"push the envelope"?forexample, by installation PC3200 or PC3500 memory, overclocking yoursystem, or running twin processors.
Unbuffered matches Registered DIMMsUnbuffered SDRAM DIMMs call for the chipsetmemory controller to manage each chip on the DIMM individually. Thereis an top limit ~ above how countless memory chips the storage controller canmanage, which restricts the total variety of unbuffered memory chipsthat the motherboard can support. Registered SDRAMDIMMs (sometimes referred to as Buffered SDRAMDIMMs) put second layer of circuitry in between thechipset storage controller and also the actual memory chips, which ineffect reduces the variety of memory chips visible to the chipsetmemory controller to a controllable number. Registered DIMMs areuncommon in desktop systems since they cost an ext and space slowerthan unbuffered DIMMs. A CL2 registered DIMM has around the samememory performance together a CL3 unbuffered DIMM. Part motherboardssupport only unbuffered DIMMs, others just registered DIMMs, and also somesupport one of two people sort. A motherboard the supports either kind mayallow utilizing one or the other, but not both at once.RDRAM systems additionally limit the variety of memory chips that have the right to beinstalled at one time. Each RIMM comprises many RDRAM memorychips, every of which is dubbed an RDRAM device.A common RDRAM chipset can support at many 32 RDRAM gadgets perchannel. If a RIMM offers 16 RDRAM chips (devices), you could installtwo the those RIMMs ~ above the channel and also still be within the upper limiton RDRAM devices. Attempting to download a third RIMM on that systemwould cause the mechanism to fail come boot. Vice versa, if girlfriend wereinstalling RIMMs that usage eight devices, three RIMMs would complete only24 devices, and also so would be in ~ the maker limitation the thatchannel.5.4.2 Chip DensityMemory modules are built fromindividual storage chips, which differ in your capacity. Chipcapacities space specified in megabits (Mb or Mbit) rather thanmegabytes (MB). Due to the fact that there room eight bits every byte, a memorymodule that uses eight chips deserve to store the variety of megabytesspecified by the megabit dimension of the chip. For example, a memorymodule that provides eight 128-Mbit chips is a 128 MB memory module.Recent storage modules may use 16-, 64-, 128-, 256-, or 512-Mbitchips. A storage module of a mentioned capacity may use fewerhigh-capacity chips or an ext low-capacity chips. For example, a 256 MBDIMM can use eight 256-Mbit chips or 16 128-Mbit chips.Although both DIMMs have 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 given capacity, it"s generally much better toinstall a single-sided DIMM when feasible because chipsets supportonly so many rows the memory, and a double-sided DIMM"uses up" two rows.However, you should not install memory that provides higher-capacity chipsthan your chipset supports. For example, the Intel 815 chipsetsupports 16-, 64-, 128-, and also 256-Mbit chips, therefore an 815-basedmotherboard can use one of two people the eight-chip or the 16-chip, 256 MBDIMM. The Intel 440BX chipset, however, supports just 16-, 64-, and128-Mbit chips, for this reason a 440BX-based motherboard might use just the16-chip 256 MB DIMM. Attempting to download a DIMM the useshigher-capacity chips than the chipset supports has actually unpredictableconsequences. Sometimes, the mechanism will simply refuse to recognizethe DIMM. Various other times, the system will recognize the DIMM, but 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. Installing an enlarge DIMM that offers 64-Mbit chipsin one Intel 875P-based motherboard results in the DIMM no beingrecognized.
If you use critical memory, which we recommend, the best means to makesure the the module you pick is compatible with your system is touse the an important Memory Selector top top the an essential home web page (http://www.crucial.com/). That tool allowsyou come specify your system or motherboard model, and also displays onlymemory modules that room compatible with your system.

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5.4.3 Parity and also ECC memory Two species of memory use extra bits tostore checksum details that deserve to detect and sometimes correctmemory errors. They are as follows:Parity memoryUses ripe bits every byte to provide an easy error detection, so simpleas to it is in useless on modern-day PCs. Most early on DIP-based pcs requiredparity memory, and also so provided nine chips every row. SIMMs, which room muchmore dependable than DIPs, made parity unnecessary. The Intel TritonPentium-class chipset and also competing chipsets eliminated support forparity memory. Current chipsets again assistance parity memory, however thereis no good reason to usage it.Although parity memory is tho sold, purchase it just if your computerrequires it. Some computer systems do not permit mixing parity and nonparitymodules. Prior to buying same memory, verify which kind is alreadyinstalled and whether your chipset deserve to mix parity with nonparitymemory. Recognize parity modules by counting the chips ~ above the module.If the number is same divisible by three, it"s aparity module. If nonparity storage is installed, or if parity memoryis installed however your chipset enables mixing types, purchase nonparitymemory. Buy parity memory only if parity storage is currently presentand her chipset go not permit mixing types.ECC memory an enhanced kind of error-checking memorythat have the right to detect single- and also multibit errors and correct every single-and part multibit errors. ECC source on mainframes, migrated tominicomputers, and also is now common on pc servers.ECC memory requires 5 extra bits to protect an 8-bit byte, six toprotect a 16-bit word, 7 to safeguard 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 assistance 168-pin DIMMs might alsosupport ECC, back ECC is not always implemented in BIOS. If yourBIOS support it, you can use ECC by installation 72-bit DIMMs andenabling ECC in Chipset Setup. The downside, however, is that 72-bitDIMMs cost about 12.5% much more than standard 64-bit DIMMs, and also enablingECC reduces storage performance, typically by about 3%. Use ECC memoryon servers when continuous uptime is critical. Perform not use ECC storage instandard desktop PCs other than those that have a large amount that memoryinstalled.
One common reason of "flipped bit"memory errors is, think it or not, cosmic rays. The much more memory youhave installed, the much more likely it is the a arbitrarily cosmic ray willimpact among the memory cells in a chip on her system, leading to thecontents of the cell to flip from a binary zero to a one or viceversa. Us don"t ~ do so to know this issue,but we"ve been told by memory specialists that forsystems v 512 MB that RAM making use of ECC versus nonparity storage is aboutan even trade-off in terms of extra cost and also lost power versusthe likelihood of memory errors. For equipment with 768+ MB, we usage ECCmemory exclusively, if the motherboard support it.
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