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Q. I am researching BABY AT and ATX form factors. I seem to be struggling on several points and wondered whether you could help. A.The problem with describing AT & ATX form factors is that there is quite an amount of overlap between the two as regards what hardware could run. In effect the main determinant of what CPU, Memory, front side bus protocols, expansion bus protocols, hard drive support, etc is actually down to the main core-logic chipset. These to a degree are independent of the form factor, although new chipsets desgined in the past three years are ATX based (they support full ATX, mini-ATX and flex-ATX). When looking at boards (and answering your questions) I will have to mention chipsets and various design trends. In effect AT (or BABY AT) is the old form factor of motherboard design. As far as I know this has been used since the days of 386 processors. All 486 designed systems are AT. The ATX standard appeared around 1996 (don't quote me on the date) with the later generation of Pentium class processors. The transition to ATX really got underway in 1997 as many high-end Socket 7 boards based on the Intel i430TX and older i430VX chipsets appeared. These though were the minority as most TX and VX boards were still made using the AT form factor. ATX only really gained momentum with the arrival of the Intel Pentium II in the summer of 1997 using the Pentium Pro derived i440FX chipset. This quickly moved to the i440LX chipset which saw the introduction features such as AGP onto the board. The Pentium II really helped the move to ATX as it was far larger than the original Pentium and could only really fit onto an ATX board away from the expansion slots. There were though a handful of rather akward looking AT boards for the Pentium II (aimed at the upgrade market) which involved the CPU being mounted above the expansion slots with a down facing heatsink & fan assembly! From Pentium II onwards the Intel processor market quickly moved to only ATX. The complicating factor in this period was the introduction of the Super Socket 7 standard designed for AMD and Cyrix processors. This was an extension of the old Socket 7 format to accomodate faster chips such as the AMD K6-2, K6 III and Cyrix MII after Intel did not grant rights to use the GTL+ bus protocol to AMD in 1997. Although AT died out in early 1998 on the Intel platform when the Celeron was introduced to replace the Pentium MMX at the low end of the Intel range, the AT form factor lived on to support the new hybrid Super Socket 7 format. The Super Socket 7 format used both AT and ATX (most were ATX, but the upgrade market has always been good for AMD so AT was required) and boards were made up until early 2001. Essentially ATX replaced AT and brought with it a number of enhancements. These included far greater power management, including a wide range of suspend functions and power saving features, boards still receiving residual power when off (AT used a hard switch to the PSU, ATX sends a signal via BIOS to the PSU to supply power) and many poor layout issues of AT being addressed. Follow on questions included: 1.What CPUs are actually supported by them? A. Again this is determined by the chipset, but the rule of thumb is: AT - Intel 386, 486, Pentium (P5, P54C), Pentium MMX (P55C), Pentium Pro, Pentium II (very seldom used with AT), AMD 386, 486, K5, K6, K6-2, K6 III, Cyrix 386, 486, 5x86, 6x86, 6x86MX, MII, IDT WinChip, WinChip 2 ATX - Intel Pentium (P54C), Intel Pentium MMX (P55C), Pentium Pro, Pentium II, Celeron, Pentium II Xeon, Pentium III, Pentium III Xeon, Pentium 4, AMD K5, K6, K6-2, K6 III, Athlon (K7, K75, Thunderbird), Duron, Athlon XP, Cyrix 6x86, 6x86MX, MII, VIA Cyrix III (all versions) There are also a large number of chipsets which straddle the cross over between AT & ATX. Some of these are: Intel i430VX, i430TX, i440FX, i440LX (rarely used on AT), VIA VP3, MVP3 (this is a Super Socket 7 chip), etc. Newer chipsets such as the Intel i440BX, i810 series, i815 series, i850, i845 series and all AMD Athlon chipsets have been ATX only. 2.Expansion slots? A. This varies according to chipset and era. I can once again only give a rule of thumb here: AT - Originally this was ISA only as you will find on many older 486 boards (normally 6 slots roughly). Later in 486 production PCI was introduced. A typical layout would be 3 PCI slots and 4 ISA with one bus interrupt shared between an ISA and PCI slot. When Pentium boards became commonplace PCI slots were standard features with a typical breakdown being 4 PCI and 3 ISA (one shared). AGP was only present on the small number of LX based AT boards, or on the more plentiful Super Socket 7 series. ATX - An early ATX board for the Pentium would feature 4 PCI and 4 ISA (circa 1997). Pentium II boards on the LX chipset were usually 1 AGP (1X), 4 PCI and 3/4 ISA (circa 1997). Early BX boards were the same as their LX counterparts but as 1998 progressed the standard gradually moved to 1 AGP (2X), 5 PCI and 2 ISA. By 2000 it was not unusual for boards to have dropped ISA altogether and appear with 1 AGP (4X), 5/6 PCI and maybe 1 AMR or CNR slot. These though are only a rule of thumb as the implementation could vary according to manufacturer. 3. Memory slots? A.Again this varies according to chipset and era. I can once again only give a rule of thumb here: AT - Accepted 30 pin Fast Page Mode RAM on 486 systems and later 72 pin RAM. Also accepted 72 pin RAM of the same variety. 72 pin EDO (Extended Data Out) was popular during the Pentium era. 168 pin SDRAM DIMM modules were introduced with later Pentium board. PC-100 was seen with Super Socket 7 boards. ATX - Accepted 72 pin EDO on Socket 7 and later Super Socket 7 systems. Mostly has been 168 pin DIMM modules of PC-66, PC-100 & PC-133 with newer boards receiving 186 pin PC1600, PC2100 & PC2700 DDR SDRAM. Also Rambus RDRAM has been used. The number of slots has been dependent upon chipset. Typically this could range from 4 to 6 SIMM sockets on AT boards through to 2-4 DIMM sockets on ATX boards. 3. Bus protocol? A.Again this varies according to chipset and era. You are probably best to deduce this from chipset support. Q. I have just upgraded my PC to an AMD Athlon/Duron and my PC keeps freezing. What's going on? A. This is a fairly simple problem to solve as it is fairly well known. The most likely cause stems from the existing PSU (Power Supply Unit) fitted in the existing ATX case which can not give an adequate power supply to the Athlon or Duron processor. This is a particular problem for users with 200 or 230 WATT Power Supply Units. The best way to solve this problem is to replace the PSU with an AMD compatible 250 or 300 WATT Power Supply Unit. This should hopefully solve the problem. If it does not solve the problem, we would recommend investigating a problem with either the CPU, motherboard or memory. Q. Can I upgrade my Super Socket 7 motherboard to an AMD Athlon or Duron? A. No. The Super Socket 7 processor line stopped with the AMD K6-2 and K6 III processor ranges. AMD's replacement in the Athlon and Duron processor ranges use a different bus protocol (Alpha EV6) from the Intel Pentium compatible K6 ranges and thus are electronically incompatible. Athlon & Duron processors also use far more pins in their sockets compared to their K6 derived relatives. Q. Can I upgrade my Socket 7 motherboard to an AMD K6-2 or K6 III? A. Most likely not. Some later Socket 7 motherboards could support K6 chips up to 300 MHz, but could not support the 100 MHz Front Side Bus used by K6-2 chips. Some boards may provide support for low-end 66 MHz K6-2 chips such as the 266 MHz and 300 MHz (66 MHz FSB version). Please refer to our Socket 7 Upgrading Guide. Q. Can I upgrade my LX motherboard to a Pentium III? A. No. The LX chipset only supported a 66 MHz Front Side Bus, wheras the Pentium III operated initially using a 100 MHz FSB and later 133 MHz FSB. The most likely upgrade path would require the use of a Celeron processor which uses a 66 MHz FSB up to 800 MHz. Please do check BIOS support from your motherboard vendor before fitting a Celeron processor as many LX boards will only support earlier PPGA Celeron chips. For more details please check our Slot 1 Upgrading Guide. Q. Whick Sockets/Slots support which processors? A. This is a rough guideline of which Sockets support which processors:
Please note that not all boards featuring the above sockets will support all listed processors. Please check with the board manufacturer for chip support. Q. Why won't my HX or VX chipset board support MMX processor's?
A. The reason why some (Not all) HX & VX chipset boards do not support MMX processors is that they do not support the core
voltages necessary to run MMX processors. The Intel Pentium MMX runs with a core voltage of 2.8v and the AMD K6-MMX runs with a core
voltage of 2.9v. These rates are lower than the 3.5v required by non MMX processors such as the Intel Pentium, Cyrix 6x86 and early AMD K5.
Many of the HX and VX boards produced were manufactured before 1997 and so do not support the split voltage requirements needed by MMX
processors. Only HX and VX chipset boards manufactured from late 1996/early 1997 onwards support the split voltage requirements necessary
for MMX processors. Baznet Solutions would advise checking the motherboard manual as to whether these lower voltages are supported. Q. Can I run an AMD K6-2 in a LX or BX Chipset motherboard?
A. Simply answered, NO! The AMD K6-2 is pin compatible with the Socket 7 connector. LX and BX chipset boards are designed for
the more recent Slot 1 motherboard connector as used with Pentium II/Celeron designs. This is electronically incompatible (as well as
physically) with the older Socket 7 connector as used by AMD and Cyrix processors. These chips run in the new Super Socket 7 motherboards
which have their own Non-Intel chipsets, such as the ALi Alladin 5 and VIA MVP3 chipsets. Q. Can I run an AMD K6-2 in a TX Chipset motherboard?
A. This largely depends upon the board. If the motherboard supports a core CPU voltage of 2.2v and high clock multipliers,
such as 4X or 4.5X then 266 Mhz and 300 MHz examples can be used. Unfortunatly, the TX chipset does not support the 100 MHz bus used by
the K6-2 and so cannot be used for examples with speeds above 300 MHz. Also many TX chipset boards do not support the voltage requirements
necessary for the running of the K6-2. Q. Diagnostic software shows Cyrix 6x86 MX PR200 as only running at 166 MHz, what is going on? A.What is going on here is perfectly normal operation for Cyrix processors, so don't worry. Although Cyrix chips are sold as being a 166, 200, 233, etc, this is not actually the speed they run at. What Cyrix use is a P rating system where they compare the chip's power to an equivalent Intel chip. The chips themselves actually run at a lower clock speed, so a Cyrix 6x86 MX PR200 actually has a clock speed of only 166 MHz and the PR233 only runs at 200 MHz. The Cyrix 6x86 MX (and now MII) are rated against an equvalent Intel Pentium MMX. Make of this system what you may, but it has always been controversial. Current Cyrix chips of PR300 & 333 both run at 250 MHz but with the 300 having a bus speed of 83 MHz and the 333 on 100 MHz. Q. Do you sell motherboards, CPU's or memory?
A.Quite simply we don't sell PC hardware. Processor Emporium (UK) is run as a non-profit making PC hardware review site.
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