IBM PC-AT

The first IBM PC ran on a 4.77 MHz Intel 8088 microprocessor. The PC came equipped with 16 kilobytes of memory, expandable to 256k. The PC came with one or two 160k floppy disk drives and an optional color monitor. The price tag started at $1,565, which would be nearly $4,000 today. What really made the IBM PC different from previous IBM computers was that it was the first one built from off the shelf parts (called open architecture) and marketed by outside distributors (Sears & Roebucks and Computerland). The Intel chip was chosen because IBM had already obtained the rights to manufacture the Intel chips. IBM had used the Intel 8086 for use in its Displaywriter Intelligent Typewriter in exchange for giving Intel the rights to IBM's bubble memory technology.

The IBM PC AT (1984) was 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 used new 16 bit expansion slots.

The PC AT had a new version of the Microsoft OS: MS-DOS 3.0 which could manage the new 5.25" floppy disk format (1.2 MB), the new hard disk capacities (20 MB and more) and allowed file sharing. It had a new keyboard too (the same we use now, more or less) with cursor keys and a key that could lock it.

Two models were launched: the PC-AT model 1 (256 KB RAM, two floppy disk units and a color screen) and the PC-AT Model 2 (512 KB RAM, one floppy disk unit, one hard disk and a color screen).This computer was revolutionary, but it was the last time IBM imposed a standard to the PC clone industry. The next year, the first PC based on a 80386 was made by Compaq and IBM failed to impose the PS/2 standard in 1986

SECOND GENERATION IBM PS/2

The IBM Personal Computer XT, often shortened to the IBM XT or simply XT, was IBM's successor to the original IBM PC. It was released as IBM product number 5160 on March 8, 1983, and came standard with a hard drive. It was based on essentially the same architecture as the original PC, with only incremental improvements; a new 16-bit bus architecture would follow in the AT. The system was largely intended for business users, and a corresponding 3270 PC featuring 3270 terminal emulation was released later in October 1983. XT stands for eXtended Technology.

The standard XT originally came with 128KB of memory, a 360KB double-sided 5 1/4" full-height floppy disk drive, a 10MB Seagate ST-412 hard drive, an Asynchronous Adapter (serial card) and a 130W PSU. The motherboard had eight 8-bit ISA expansion slots, and an Intel 8088 microprocessor running at 4.77 MHz (with a socket for an 8087 math coprocessor); the operating system usually sold with it was PC-DOS 2.0 and above. The eight expansion slots were an increase over the five in the IBM PC, although three were taken up by the floppy drive adapter, the hard drive adapter, and the Async card. The basic specification was soon upgraded to have 256KB of memory as standard. http://en.wikipedia.org/wiki/IBM_5160

IBM Personal System/2
Developer	International Business Machines Corporation (IBM)
Type	Professional Computer
Release date	April, 1987
CPU	8 MHz Intel 8086

The Personal System/2 or PS/2 was IBM's third generation of personal computers. The PS/2 line, released to the public in 1987, was created by IBM in an attempt to recapture control of the PC market by introducing an advanced proprietary architecture. Although IBM's considerable market presence ensured the PS/2 would sell in relatively large numbers, the PS/2 architecture ultimately failed in its bid to return control of the PC market to IBM. Due to the higher costs of the closed architecture, customers preferred competing PCs that extended the existing PC architecture instead of abandoning it for something new. However, many of the PS/2s innovations, such as the 1440 kB 3.5-inch floppy disk format, 72-pin SIMM, the PS/2 keyboard and mouse ports, and the VGA video standard, went on to become standards in the broader PC market.

The AS/400 was introduced in 1988 by IBM as a minicomputer for general business and departmental use. It underwent several rebrandings until its last rebrand in 2006 to the name of IBM System i. It remained in production until April 2008 when it was replaced by the IBM Power Systems line.

The ThinkCentre was released in 2003, replacing the IBM NetVista. In 2005, Lenovo purchased the IBM PC division, and the ThinkCentre along with ThinkPad, are now produced by