MODELS

PC

IBM PC 5150.

The CGA video card, with a suitable modulator, could use an NTSC television set or an RGBi monitor for display; IBM's RGBi monitor was their display model 5153. The other option that was offered by IBM was an MDA and their monochrome display model 5151. It was possible to install both an MDA and a CGA card and use both monitors concurrently if supported by the application program. For example, AutoCAD, Lotus 1-2-3 and others allowed use of a CGA Monitor for graphics and a separate monochrome monitor for text menus. Some model 5150 PCs with CGA monitors and a printer port also included the MDA adapter by default, because IBM provided the MDA port and printer port on the same adapter card; it was in fact an MDA/printer port combo card.

Although cassette tape was originally envisioned by IBM as a low-budget storage alternative, the most commonly used medium was the floppy disk. The 5150 was available with one or two 5-1/4" floppy drives - with two drives the program disc(s) would be in drive A, while drive B would hold the disc(s) for working files; with one drive the user had to swap program and file discs into the single drive. For models without any drives or storage medium, IBM intended users to connect their own cassette recorder via the 5150's cassette socket. The cassette tape socket was physically the same DIN plug as the keyboard socket and next to it, but electrically completely different.

A hard disk could not be installed into the 5150's system unit without changing to a higher-rated power supply. The "IBM 5161 Expansion Chassis" came with its own power supply and one 10 MB hard disk and allowed the installation of a second hard disk. The system unit had five expansion slots, and the expansion unit had eight; however, one of the system unit's slots and one of the expansion unit's slots had to be occupied by the Extender Card and Receiver Card, respectively, which were needed to connect the expansion unit to the system unit and make the expansion unit's other slots available, for a total of 11 slots. A working configuration required that some of the slots be occupied by display, disk, and I/O adapters, as none of these were built into the 5150's motherboard; the only motherboard external connectors were the keyboard and cassette ports.

The simple PC speaker sound hardware was also on board.

The original PC's maximum memory using IBM parts was 256 kB, achievable through the installation of 64 kB on the motherboard and three 64 kB expansion cards. The processor was an Intel 8088 running at 4.77 MHz, 4/3 the standard NTSC color burst frequency of 315/88 = 3.57954[a] MHz. (In early units, the Intel 8088 used was a 1978 version, later were 1978/81/2 versions of the Intel chip; second-sourced AMDs were used after 1983). Some owners replaced the 8088 with an NEC V20 for a slight increase in processing speed and support for real mode 80186 instructions. The V20 gained its speed increase through the use of a hardware multiplier which the 8088 lacked. An Intel 8087 co-processor could also be added for hardware floating-point arithmetic.

IBM sold the first IBM PCs in configurations with 16 or 64 kB of RAM preinstalled using either nine or thirty-six 16-kilobit DRAM chips. (The ninth bit was used for parity checking of memory.) After the IBM XT shipped, the IBM PC motherboard was configured more like the XTs motherboard with 8 narrower slots[dubious – discuss], as well as the same RAM configuration as the IBM XT. (64 kB in one bank, expandable to 256kB by populating the other 3 banks.)

Although the TV-compatible video board, cassette port and Federal Communications Commission Class B certification were all aimed at making it a home computer, the original PC proved too expensive for the home market. At introduction, a PC with 64 kB of RAM and a single 5.25-inch floppy drive and monitor sold for US $3,005 (equivalent to $7,822 in 2016), while the cheapest configuration (US $1,565) that had no floppy drives, only 16 kB RAM, and no monitor (again, under the expectation that users would connect their existing TV sets and cassette recorders) proved too unattractive and low-spec, even for its time (cf. footnotes to the above IBM PC range table). While the 5150 did not become a top selling home computer, its floppy-based configuration became an unexpectedly large success with businesses.

XT

The "IBM Personal Computer XT", IBM model 5160, was introduced two years after the PC and featured a 10 megabyte hard drive. It had eight expansion slots but the same processor and clock speed as the PC. The XT had no cassette jack, but still had the Cassette Basic interpreter in ROMs.

The XT could take 256 kB of memory on the main board (using 64 kbit DRAM); later models were expandable to 640 kB. The remaining 384 kilobytes of the 8088 address space were used for the BIOS ROM, adapter ROM and RAM space, including video RAM space. It was usually sold with a Monochrome Display Adapter (MDA) video card or a CGA video card.

The eight expansion slots were the same as the model 5150 but were spaced closer together. Although rare, a card designed for the 5150 would be wide enough to obstruct the adjacent slot in an XT.Because of the spacing, an XT motherboard would not fit into a case designed for the PC motherboard, but the slots and peripheral cards were compatible. The XT expansion bus (later called "8 bit Industry Standard Architecture" (ISA) by competitors) was retained in the IBM AT, which added connectors for some slots to allow 16-bit transfers; 8 bit cards could be used in an AT.

XT/370

The "IBM Personal Computer XT/370" was an XT with three custom 8-bit cards: the processor card (370PC-P) contained a modified Motorola 68000 chip, microcoded to execute System/370 instructions, a second 68000 to handle bus arbitration and memory transfers, and a modified 8087 to emulate the S/370 floating point instructions. The second card (370PC-M) connected to the first and contained 512 kB of memory. The third card (PC3277-EM), was a 3270 terminal emulator necessary to install the system software for the VM/PC software to run the processors.

The computer booted into DOS, then ran the VM/PC Control Program.

PCjr

The "IBM PCjr" was IBM's first attempt to enter the market for relatively inexpensive educational and home-use personal computers. The PCjr, IBM model number 4860, retained the IBM PC's 8088 CPU and BIOS interface for compatibility, but its cost and differences in the PCjr's architecture, as well as other design and implementation decisions, eventually led to the PCjr, and the related IBM JX, being commercial failures.

Portable

The "IBM Portable Personal Computer" 5155 model 68 was an early portable computer developed by IBM after the success of Compaq's suitcase-size portable machine (the Compaq Portable). It was released in February, 1984, and was eventually replaced by the IBM Convertible.

The Portable was an XT motherboard, transplanted into a Compaq-style luggable case. The system featured 256 kilobytes of memory (expandable to 512 kB), an added CGA card connected to an internal monochrome (amber) composite monitor, and one or two half-height 5.25" 360K floppy disk drives. Unlike the Compaq Portable, which used a dual-mode monitor and special display card, IBM used a stock CGA board and a composite monitor, which had lower resolution. It could however, display color if connected to an external monitor or television.

AT

The "IBM Personal Computer/AT" (model 5170), announced August 15, 1984, used an Intel 80286 processor, originally running at 6 MHz. It had a 16-bit ISA bus and 20 MB hard drive. A faster model, running at 8 MHz and sporting a 30-megabyte hard disk was introduced in 1986.

The AT was designed to support multitasking; the new SysRq (System request key), little noted and often overlooked, is part of this design, as is the 80286 itself, the first Intel 16-bit processor with multitasking features (i.e. the 80286 protected mode). IBM made some attempt at marketing the AT as a multi-user machine, but it sold mainly as a faster PC for power users. For the most part, IBM PC/ATs were used as more powerful DOS (single-tasking) personal computers, in the literal sense of the PC name.

Early PC/ATs were plagued with reliability problems, in part because of some software and hardware incompatibilities, but mostly related to the internal 20 MB hard disk, and High Density Floppy Disk Drive.

While some people blamed IBM's hard disk controller card and others blamed the hard disk manufacturer Computer Memories Inc. (CMI), the IBM controller card worked fine with other drives, including CMI's 33-MB model. The problems introduced doubt about the computer and, for a while, even about the 286 architecture in general, but after IBM replaced the 20 MB CMI drives, the PC/AT proved reliable and became a lasting industry standard.

IBM AT's Drive parameter table listed the CMI-33 as having 615 cylinders instead of the 640 the drive was designed with, as to make the size an even 30 MB. Those who re-used the drives mostly found that the 616th cylinder was bad due to it being used as a landing area.

AT/370

The "IBM Personal Computer AT/370" was an AT with two custom 16-bit cards, running almost exactly the same setup as the XT/370.

Convertible

The IBM PC Convertible, released April 3, 1986, was IBM's first laptop computer and was also the first IBM computer to utilize the 3.5" floppy disk which went on to become the standard. Like modern laptops, it featured power management and the ability to run from batteries. It was the follow-up to the IBM Portable and was model number 5140. The concept and the design of the body was made by the German industrial designer Richard Sapper.

It utilized an Intel 80c88 CPU (a CMOS version of the Intel 8088) running at 4.77 MHz, 256 kB of RAM (expandable to 640 kB), dual 720 kB 3.5" floppy drives, and a monochrome CGA-compatible LCD screen at a price of $2,000. It weighed 13 pounds (5.8 kg) and featured a built-in carrying handle.

The PC Convertible had expansion capabilities through a proprietary ISA bus-based port on the rear of the machine. Extension modules, including a small printer and a video output module, could be snapped into place. The machine could also take an internal modem, but there was no room for an internal hard disk.

Next-generation IBM PS/2

The IBM PS/2 line was introduced in 1987. The Model 30 at the bottom end of the lineup was very similar to earlier models; it used an 8086 processor and an ISA bus. The Model 30 was not "IBM compatible" in that it did not have standard 5.25-inch drive bays; it came with a 3.5-inch floppy drive and optionally a 3.5-inch-sized hard disk. Most models in the PS/2 line further departed from "IBM compatible" by replacing the ISA bus completely with Micro Channel Architecture.