Contents1. Executive Summary......................................................................................................72. ATX Form-factor Overview...........................................................................................83. Layout .....................................ATX SpVersion 2.1Revision HistoryChanges from Version 2.03 to Version 2.1Global change-Removed references to mini-ATXSection 2--Replace existing text with new text that adds requirement for atX12V connector; substituterevised FigureSection 3.3- Add atX12v power connector information to table 3Section 3.3.2-Replace existing text with new text that includes the 12v requirement for processor voltageregulatorsSection 3.4-Moved text in Section 3. 4 under a new subheading, 3.4.1. Added subheading, 3.4.2,tospecify secondary side height constraints. Revised Figure 7 to reflect an increase in the maximumcomponent height restriction. Zones C, D, and e formerly specified three different height restrictionsThis revision replaces those three zones(C, D, and e) with one maximum component height restrictionzone( c) for the entire region. Added two sentences at the end of the note that follows Figure 7Section 4-Replace existing text with new text that adds the 12v connector and a reference to theATX/ATX12V Power Supply Design GuideSection 4.2 Add references to the aTX12V connector; substitute revised Figure 10Section 4. 4-Add new Table 10 that lists wire color code for atX12V power suppliesSection 6-Update Web site URL for ATX information and document downloadinChanges fromⅤ ersion202toⅤ ersion2.03Replaced seven occurrences of the erroneous name"microatX with the correct name"Mini-AtX. Theerror was introduced accidentally in Version 2.02. The Mini-ATX form factor is 11.2 X8.2"(284mm x208mm; the Mini-ATX form factor referred to in this ATX Specification is Not the same as the microATXform factor, which is described in a separate specificationChanges from Version 2.01 to Version 2.02Section 3. 3. 5--Replaced figures 4 and 5Section 4.2.1--Added new section to define Aux Power Connector; renumbered the subsequent sectionsfigures and tables accordinglySection 4.2.2.3--Replaced Figure 1 1 to better explain the power supply timingSection 4.2.3--Corrected two values in Table 7, Voltage Tolerances:-5VDC and-12VDC should complyto+ 10%0, not +5%. This change was made to match the newly released Intel atX Power Supply designGuide, Version 0.9Section 4.4-Corrected Table 9: the 1394R signal is carried on Pin 4 and Pin 6 is reserved. This matchesthe information shown in Figure 12Section 6--Added section to provide the Internet location of the atX home page, for access to documentswith information beyond the requirements of this atX specificationChanges from Version 2.0 to Version 2.01Section 2Updated Figure I to reflect recommendations implemented with Version 2.0Section 3.2-Modified Figure 2 to clarify motherboard mount requirementsSection 3.3-Updated table of requirements to reflect changes in the section outlined belowSection 3.3.5--Rewrote text to clarify requirementsContinuedPage 3ATX Specification - Version 2.1Section 3.3.5-Reduced keepout zone requirement to 0. 1"(2.5 mm). This change was based on feedbackfrom chassis manufacturers and is the most significant requirement change with respect to the chassisSection 3. 3.5--Added recommendation to avoid paint within the keepout zoneSection 3.3.5--Replaced Figure 4 to clarify chassis 1/O aperture requirements. Tolerances were added todimensionsSection 3. 3.5--Changed Figure 5 to define connector placement limitations on the motherboard. This is anew recommendation for motherboard designers to ensure clearance between the chassis andmotherboard connectors for the lo shieldSection 3. 3. 5--Modified Figure 6 to remove redundant dimensions, and removed Figure 7 completelySection 4.3.2--Completely redefined FanC signal description, and removed Figure 15 completelyMinor edits were made throughout the document to improve readability and to correct minor typographicalor grammatical errorsChanges from Version 1. 1 to Version 2.0Section 3. 2--Changed the optional mounting hole to a required hole in chassis implementations. Changeda previously required mounting hole to"not neededSection 3.3.5--Added information and drawing to clarify 1O aperture requirements. Added corner radiusinformation to the specification for claritySection 3. 4--Changed height restrictions to facilitate future processor and onboard technologiesSection 4-Added an explanation of the intent regarding the direction of air travel for cooling. Removedthe external fan shown on the drawing of a suggested aTX power supply. Added a caution aboutexternal power supply fans. Added comments and drawings for duct mountingSection 4.2--Added explanations for PS_ON#, PWR_OK, 5VSB power supply lines. The 3.3VDC powerrail and soft-power control signals are being changed to requiredSection 4.3--Added optional power connector for fan control, fan monitor, IEEE-1394 voltages, andremote 3. 3 volt sensingSection 4.4--Added a section to give a suggested color coding for power supply wiringSection 4.5-Added a section suggesting a venting solution for power suppliesSection 5--Added chassis considerationsAdded tables throughout the specification for clarification and easy reference of recommended andrequired featuresgeATX SpVersion 2.1Contents1. Executive Summary…■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■a■■D■■72 AtX Form-factor Overview■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■重■■3. Layout…93.1 Board Size93.2 Mounting Hole Placement……3.3 Connector Placement33.1 Expansion slots…3.32 Power Input..…133.3.3 Disk 1/O3.34 Front pane|M/O..…………133.3.5 Back Panel 1/o3.3.6 Memory Sockets163.3.7 Processor163.4 Height Constraint163.4.1 Primary(Component) Side Height Constraints163.4.2 Secondary(Bottom/Solder) Side Height Constraints184, Power Delivery……94.1 Power Supply Connectors4.1.1 Aux Power Connector for 250 W and 300 W Configurations204.1.2 2x2 Connector204.1.3 Power Signal control Definitions量1画204.1.4 Voltage Tolerances214.2 Optional power Connector214.2.1 FanM Signal224.2.2 FanC Signal224.2.3 3.3V Sense Line.234.2.41394∨Pin234.2.51394RPin235,0 ther atx chassis considerations……………245.1 Venting245.2 Power Supply Mounting246. Additional Information■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■a■a24Page 5ATX Specification -Version 2.1FiguresFigure 1. Summary of ATX Chassis FeaturesFigure 2. ATX and microATX Form Factor Mounting Holes10Figure3. Sample atX layout diagram……Figure 4. Chassis Back Panel IO Aperture Requirements14Figure 5. Motherboard l/o Connector Zone RecommendationFigure6. EXample Multimedia l/ O Back Panel……………Figure 7. ATX Motherboard Maximum Component Height Restrictions17Figure 10. ATX Power Supply Connector ConfigurationFigure 9: 2X2 Connector Configuration20Figure 12. Optional Power Supply Connector Configuration22Figure 13. Simple Implementation of a Fan Monitor Circuit22TablesTable 1. ATX Feature SummaryTable 2. Motherboard Mounting Hole Locations9Table 3. Connector LocationsTable4. Height Constraints.………………………………………16Table 5. Aux Power Connector for High 3. 3V or 5v current Configurations20Table 6. Voltage tolerances21Page 6ATX Specification - Version 2.11. Executive SummaryATX was developed as an evolution of the Baby-at form factor and was defined to address four majorareas of improvement: enhanced ease-of-use, better support for current and future 1/O, better support forcurrent and future processor technology, and reduced total system costATX combines the best functionality from the form factors that dominated the computer industry in theearly 1990s: the high integration of LPX and the expandability of Baby-AT. The aTX form factor isessentially a Baby AT motherboard rotated 90 degrees within the chassis enclosure and providing a newmounting configuration for the power supply. The processor is relocated away from the expansion slots,llowing them all to hold full length add-in cards. The longer side of the board is used to host more onboard io. table i summarizes the atx featuresA change to the system form factor is ultimately of little benefit if it does not reduce overall system costATX has achieved cost reduction in a number of waysMaterial cost of cables and add-in cards is reduced because more io can be integrated down onto theboard and because the hard drive and floppy connectors can be better positioned, allowing the use ofshorter cablesAnother benefit of integrated 1O down is the potential for lower EMI emissions with the removal ofserial and parallel cables that can act like antennasManufacturing time and inventory holding costs are reduced bccause the number of cables in thesystem is reducedVideo-playback enhanced graphics and audio, the main hardware building blocks to supportmultimedia, are becoming a standard on many PCs; at the entry level, these features are quicklybecoming a commodity. To reduce cost in a highly dollar-sensitive market segment, it makes sense tomigrate these features down to the motherboard itselfThe ATX specification is written as an open specification for the industry, designed to add value to PCarchitectureTable 1. ATX Feature SummaryFeatureBenefitDouble height flexible l/o Lower system costpanel allows higherFewer cablesintegrationImproved reliabilityShorter assembly timeSupport for connectivity and l/o standards like USB, TV in/out, ISDN, etcIntegrated graphics allows use of unified frame buffer architectureRelocated drive I/O means Reduced costshorter cablesSupport for faster drives such as Plo Mode 4/5 IdE drivesRelocated processor and All full-length expansion slotsmemoryEase of use, upgrading the processorEase of use, upgradingEase of use, adding cardsRelocated processor allows easier use of bulk capacitance and voltage regulation circuitrygeATX Specification - Version 2.12 ATX Form-factor OverviewThe ATX form factor allows for processor relocation away from the expansion slots, allowing the longerside of the board to be used to host more on-board lo. For processor voltage regulators that have beendesigned for 12V input, an additional 12v power connector must be added atX power supplies with therequired 12V current and associated connector are designated ATXI2V. The atX12v mating connectoris shown in Figure 10. Details on the power supply can be found in the ATX/ATX12V Power SupplyDesign Guide(see Section 6 for URL from which the document can be downloaded)Double HighExpandableSystem faCPUPSUCPU located nearpower supplyFull LengthCard Slots12 V Connector next.一Easy to accessto Voltage Regulatormemory modules5.253.5Single powerFloppy/DEBayBconnectorconnectors closeto peripheral baysFigure 1. Summary of AtX chassis Featuresge 8ATX Specification - Version 2.13. LayoutThe following sections describe the mechanical specification of the ATX form factor motherboardincluding physical size, mounting hole placement, connector placement, and component height constraints3.1 Board sizeA full size atX board is 12 wide by 9.6"deep(305mm x 244mm). This allows many ATX form factorchassis to accept microatX boards as well3.2 Mounting Hole PlacementTable 2. Motherboard Mounting hole locationsFeatureStatus CommentMotherboard mounting holeRequired See Figure 2 for an overview and Figure 3 for exact locations. AlllocationsATX board mounting locations shown should be implemented for fullATX 2. 1 complianceWhere possible, the ATX mounting holes line up with mounting holes used for microATX boards. Threholes have been defined to provide mechanical support along the front edge of the full size atx boardFigure 2 shows the relative outlines of the atX and microaTX boards. This figure uses letter calloutsto show the general location of the mounting holes for the ATX and microATX form factors. Theaccompanying table indicates which holes are required for cach form factorFigure 3 shows the exact location(dimensions)of the mounting holes for ATX boardsMust be usedAll atX board mounting locations listed in the table in Figure 2 should be implemented for chassisassemblies to achieve full ATX 2. I compliance and to provide proper support for the board in these areasThe hole at F in Figure 2(upper right corner of the AtX board) must be implemented in all ATX 2compliant chassis assemblies to accommodate boards requiring this mounting hole. This hole was labeledoptional in the atX 1.I specification. Note that changing this mounting location from optional to requiredmay not accommodate all aTX 1.0-and l I-compliant motherboards. To accommodate thesemotherboards, a removable standoff may be used. All ATX 2. 1-compliant motherboards should implementthis mounting location or allow for a standoff in this area by implementing a component and trace keepoutNo longer usedThe hole at b in Figure 2 was previously required along the rear edge of the board. This location is notrequired for ATX designs. If it is desired to implement a board mount in this area, a removable standoffshould be used to avoid problems with boards that do not use this mounting locationPage 9ATX Specification - Version 2.1NOT TO SCALEREAR of board2”(305mm)6.25 wide rearI/O shield9.6”(244mm)○ACPCIISA/AGPlocations (4 max)9.6”(244mmn)○G●R○sH○KKey, mounting holesNcw for microatXFRONT of boardmicroAtXATXForm factor Mounting holeNoteslocationsATXA,C,F,G,H,J,K,L,M Hole F must be implemented in all ATX 2.1-compliantchassis assemblies; it was optional in the aTX 1.1speciticationmicroATXB.C.FHLMRSHoles r and s are added for microatX form factorHole b was defined in full at formatFigure 2. ATX and micro ATX Form Factor Mounting Holesge 10