A brief review on PC/XT/AT/ATX

                                                            A brief review on PC/XT/AT/ATX
                                                              -----------2004-11-2 (C) Gr1x
     This topic may seems boring at first sight, yeah, we've saw PC/XT/AT many times when reading sth about computer architecture. But many books just mension these words without explaining them, so I'm trying to guide u through the early stage of PC development, hoping it'll be useful for u.
    The following information is downed form the Internet, but may not complete and I cann't remember where, please let me know if u get more.
     In the early part of 1980, IBM decided to create a microcomputer (up to this date, IBM produced only mini and mainframes). They didn't really know that they wanted and they didn't think for one second that producing microcomputer was a profitable business (who would have thought!)!
    After hesitation between the Intel 8086 (16 bit) and the Motorola MC68000, they decided to use the Intel 8088 (8 - 16 bit) processor, as the two other ones were considered too powerful! Then they asked to Digital Research (the creators of CP/M) to create an operating system for their new computer, as DR was not very interested, they then asked a small company (famous for its BASIC Programming Language) to write the operating system: Microsoft.
    Microsoft wasn't capable of doing it, Bill Gates bought the rights to a small, hacked OS written by a small company called Seattle Computer Products: QDOS (which reportedly stood for "Quick and Dirty Operating System", which itself bears a striking resemblance to CP/M) which became PC-DOS and then later MS-DOS!
   The original IBM PC wasn't very powerful (and was certainly less powerful than lot of 8 bit computers at the time). The very first PC had only 16 KB RAM and no floppy disk units, they used cassettes to load & store programs (notice that the commands to handle the cassette drives were present in the operating system all the way up to MS-DOS 5!). 
  Then in 1983 the XT stands for EXtended Technology  was introduced. The IBM PC XT is the successor of the IBM PC.
It has enhanced features: CGA graphic card, hard disk, more memory, and no more tape port.In addiditon to the removal of the cassette port, the XT also had eight 8-bit ISA expansion slots VS the PC's five. The XT's slots were also positioned closer together, the same spacing all PCs still use today. This made old PC's totally worthless because you couldn't buy an XT clone board and drop it into a PC case. Eight slots was a huge boon to the "power user" who had previously found himself having to pick and choose what upgrades to install in the paltry five slots of the PC.
    The IBM PC AT is the successor of the PC and the XT. IBM added a lot of new features: they abandoned the old Intel 8086 to the Intel 80286, so the PC AT uses new 16 bit expansion slots. 
    The PC AT has a new version of the OS: MS DOS 3.0 which can use the new floppy disk format (1.2 MB), the new hard disk capacity (20 MB) and allows file sharing. It has a new keyboard too (the same we use now, more or less) with cursor keys and a key that can lock it. 
   ......
   Now,it's ATX, the modern-day shape and layout of PC motherboards. It improves on the previous standard, the Baby AT form factor, by rotating the orientation of the board 90 degrees. This allows for a more efficient design, with disk drive cable connectors nearer to the drive bays and the CPU closer to the power supply and cooling fan.
    So, just try to make a conclusion, we get these: PC--->PC/XT(EXtended Technology)--->PC/AT(Advanced Technology)-->ATX(Advanced Technology Extented). Simple, then why I write so much, just wanna to practice my English :) Sorry for inconvenience!