Question:
What is the difference between a modern motherboard to an old one??
superboy22_h
19 years ago
will you ellaborate the difference between PC/TX, and an AT and an ATX motherboards???
Four answers:
WILLIAM P
19 years ago
The main differences between the xt and at were that the xt used an 8bit 8088 processor and bus. The AT used a 16bit isa bus and the 80286 processor,



It also had 15 IRQs and 7 DMA channels, expanded from 8 IRQs and 4 DMA channels for the PC. (IRQ 8–15 are cascaded through IRQ 2, which leaves 15 active instead of 16)

* 16 MiB maximum memory supported by the 24-bit address bus, compared to the PC's 640 kiB

* battery backed Real-time clock on motherboard with 50 bytes CMOS memory available for power-off storage of BIOS parameters. (the basic PC had required either manual setting of its software clock using Time and Date commands, or the addition of an accessory expansion card with real-time clock, to avoid the default 01-01-80 file date)

* 84-key AT keyboard layout – the "84th key" being i.e. System Request; numerical keypad now clearly separated from main key group; also added indicator LEDs for Caps lock/Scroll lock/Num lock. The AT keyboard uses the same 5-pin DIN connector as the PC keyboard, and is electrically compatible with it, but it generates different keyboard scan codes.

* 1.2 MiB 5 1/4 inch floppy disk drive (15 sectors of 512 bytes, 80 tracks, 2 sides) stored over three times as much data as the 360 kiB PC floppy disk (9 sectors of 512 bytes, 40 tracks, 2 sides)

* 20 MB hard disk drive was twice as fast (about 40 msec) as the PC XT's 10 MB drive, although the early drives manufactured by Computer Memories (CMI) had a 25–30% failure rate after one year. This was attributed partly due to failure to automatically retract the read/write heads when the computer was powered off, and partly due to a bug in DOS 3.0 FAT algorithm.

* optional Enhanced Graphics Adapter with 16 display colors from a 64 color palette on a 640 x 350 pixel resolution screen

* optional Professional Graphics Controller with 256 colors from a 4096 color palette and 640 x 480 resolution and accelerated 2D and 3D display functions for Computer Aided Design (CAD) applications

* PC-DOS 3.0 was released to support the new AT features



An ATX power supply does not directly connect to the system power button, allowing the computer to be powered off via software. However, many ATX power supplies have a switch on the back to ensure no power is flowing to the motherboard (a trickle of energy is normally sent to an ATX-style motherboard even if the computer appears to be "off"). Because the ATX PSU uses the motherboard's power switch, turning on the power in situations that do not utilize an ATX motherboard is possible by shorting the green wire from the ATX connector to any black wire on the connector (or ground).



The power supply's connection to the motherboard was changed. Older AT power supplies had two similar-looking connectors that could sometimes inadvertently be plugged in incorrectly, generally causing short-circuits in the motherboard and causing it to fail. ATX used one large keyed connector instead, which made installation much easier and safer. The new connector also provided a 3.3 volt connection removing the need for motherboards to derive this voltage from one of the other power rails. Some motherboards, particularly late model AT form factor ones, supported both AT and ATX PSUs. With the introduction of the Pentium 4 this connector was deemed inadequate and an extra 4-pin 12 volt connector was added and this was also later adopted by later Athlon XP and Athlon 64 systems. Some high end systems have also used other connectors to bring in more power. Some high power graphics cards also needed extra power but this was generally delivered through a 4-pin molex connector as used for hard drives and CD-ROM drives.



On the back of the system, some major changes were made. The AT standard only had a keyboard connector and the slots where the backplates of plug in cards went. Any other onboard interfaces (such as serial and parallel ports) had to be connected via flying leads to connectors which were mounted either on spaces provided by the case or brackets placed in unused expansion slot positions. ATX allowed each motherboard manufacturer to put these ports in a rectangular area on the back of the system, with an arrangement they could define themselves (though a number of general patterns depending on what ports the motherboard offers have been followed by most manufacturers). Generally the case comes with a snap out panel, also known as a I/O plate, reflecting one of the common arrangements. If necessary I/O plates can be replaced, to suit the arrangement on the motherboard that is being fitted, and are usualy included when purchasing a motherboard. Panels were also made that allowed fitting an AT motherboard in an ATX case.



ATX also made the PS/2 keyboard and mouse connectors ubiquitous. AT systems often used a 5 pin DIN connector for the keyboard, and were generally used with serial port mice (although a PS/2 mouse port was not unheard of).



The official specifications were released by Intel in 1995, and have been revised numerous times since, the most recent being version 2.2[1], released in 2004.



The ATX form factor has had five main power supply designs throughout its lifetime:



* ATX - 20 pin connector (Used through Pentium III and early Athlon XP)

* WTX - 24 pin connector (Pentium II and III, Xeon and Athlon MP)

* AMD GES - 24 pin main connector, 8 pin secondary connector (some dual-processor Athlon)

* ATX12V - 20 pin main connector, 4 pin secondary connector, 8 pin tertiary connector (Pentium 4 and mid/late Athlon XP & Athlon 64)

* EPS12V - 24 pin main connector, 8 pin secondary connector, 8 pin tertiary connector (Xeon and Opteron) defined in SSI specification

* ATX12V 2.0 - 24 pin main connector, 4 pin secondary connector (Pentium 4 and Athlon 64 with PCI Express)



A full size ATX board is 12" wide by 9.6" deep (305 mm x 244 mm). This allows many ATX form factor chassis to accept microATX boards as well.
b_jay82
19 years ago
The main difference would be the power. AT motherboards had these 2 connectors that plugged in to the Motherboard, you had to press the power button in order to turn off the computer. The ATX motherboards have 1 connector, and once you click on shut down, you can set the power to go off automatically instead of pressing the power button. It gave you more power options.
shell4678
19 years ago
i couldnt tell ya dont no nothing about it
CrazyFingers
19 years ago
what he said


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