IBM Personal Computer XT
| Company type | Product line |
|---|---|
| Industry | Computer hardware |
| Predecessor | IBM Personal Computer 5150 |
| Founded | March 8, 1983 |
| Successor | IBM Personal System/2 Model 30 |
| Products | Personal computer |
The IBM Personal Computer XT (model 5160, commonly referred to as the PC/XT) represents the second iteration in the IBM Personal Computer lineup, introduced on March 8, 1983. While bearing a strong resemblance to the initial IBM PC 5150 (released in 1981), it distinguished itself by incorporating an internal hard drive and offering additional expansion slots.
Name
IBM never formally clarified the meaning of "XT" in its official materials or advertising. However, some interpretations suggest it stands for "eXtended Technology" or simply "eXTended."
Features
Rather than a revolutionary redesign, the XT was regarded as a modest enhancement over its predecessor. Notable upgrades compared to the original IBM PC include:
- Increase of expansion slots from five to eight
- Minimum base RAM expanded to 128 KB
- ROM configuration changed from five 8KB chips to two 32KB integrated circuits
- Inclusion of a 10 MB hard drive on most versions, utilizing a disk controller with Xebec integrated circuits
- Pre-installed with PC DOS version 2.0
- Removal of the cassette interface's 5-pin DIN connector
Other technical aspects largely remained consistent with the original IBM PC.
Expansion slots
The original IBM PC featured five expansion slots, which were quickly occupied by essential cards such as video adapters, disk controllers, and printer interfaces. This limited further expandability and often forced users to interchange cards depending on their needs. Some clone manufacturers addressed this limitation by integrating multiple components directly onto the motherboard, thereby freeing up expansion slots, or by designing multifunction cards that combined several capabilities into one slot.
The XT addressed expandability by adding three extra slots, bringing the total to eight. Although these slots retained compatibility with the original PC design, two of the newly added slots located behind the hard drive bay could not accommodate full-length cards due to physical space restrictions within the chassis. Additionally, a narrower spacing between slots prevented certain multi-board cards from fitting properly.
Expansion unit
The 5161 Expansion Unit shares the XT’s enclosure and power supply but replaces its system board with a backplane that offers eight card slots. It connects to the main computer through an Extender Card and a Receiver Card linked via a proprietary cable. The unit comes equipped with a 10 MB hard drive and has room for an additional drive, allowing for expanded storage options.
Although it supports memory installation, RAM placed in the Expansion Unit experiences increased wait states because of the Extender Card interface; therefore, adding memory directly to the main system board is generally preferred. The 5161 is compatible with both the XT and the original IBM PC (model 5150).
Other features
PC DOS version 2.0 introduced support for a 9-sector floppy disk format, which raised single-sided disk capacity to 180K and double-sided capacity to 360K, compared to earlier disks formatted with 8 sectors per track.
During its initial two years on the market, the XT was not available in a floppy-only configuration despite including a ribbon cable designed for two floppy drives; users had to rely on the 5161 expansion chassis to add a second floppy drive.
Similar to its predecessor, the XT featured IBM BASIC stored in ROM and BIOS firmware that displayed memory size during POST (Power-On Self-Test). The desktop-style case weighed approximately 32 pounds and measured about 19.5 inches wide by 16 inches deep by 5.5 inches tall.
The motherboard provided an optional socket for an Intel 8087 floating-point coprocessor, which enhanced performance for computation-intensive tasks like computer-aided design when paired with compatible software.
The power supply was upgraded from that of the original PC to deliver 130 watts. U.S. versions operated exclusively on 120 V AC power, while subsequent international models supported 240 V input without altering wattage specifications.
Revisions and Variants
IBM introduced multiple submodels of the XT series.
The 3270 PC, a variation of the XT featuring 3270 terminal emulation capabilities, was launched in October 1983.
In 1985, the 068 and 078 submodels were released, featuring dual-floppy drives without hard disk options, and incorporating new video adapters such as the Enhanced Graphics Adapter and Professional Graphics Adapter.
By 1986, IBM rolled out models equipped with motherboards supporting between 256 KB and 640 KB of RAM, transitioning to half-height disk drives.
The 268, 278, and 089 submodels came with 101-key keyboards, which were modified versions of the IBM Model M using the XT communication protocol but omitted LED indicators.
Meanwhile, submodels 267, 277, and 088 preserved the original keyboard design but upgraded to include 3.5" floppy drives and swapped the full-height 10 MB hard drives for half-height Seagate ST-225 drives with a capacity of 20 MB.
Among these, submodel 788 stood out as the sole XT variant equipped with a standard Color Graphics Adapter.
The XT/370 series was based on submodels 568, 588, and 589; these featured an additional co-processor card capable of executing System/370 instructions. Additionally, there was an XT version fitted with a Series/1 co-processor; however, it was assigned a distinct System Unit number (IBM 4950).
XT 286
Unveiled in 1986, the XT 286 (model number 5162) incorporated a 6 MHz Intel 80286 CPU. Although it was marketed as a lower-tier alternative to the IBM AT, its performance often surpassed many contemporaneous AT systems utilizing the same processor speed due to its zero-wait state memory configuration.
The standard setup included 640 KB of RAM, a high-density AT-style floppy drive with a capacity of 1.2 MB, and a hard disk sized at 20 MB. Despite these specifications, it faced criticism regarding its cost-effectiveness in the marketplace.
Powering the XT 286 was a 157-watt power supply unit capable of internally switching between 115 V and 230 V AC inputs.
Both the original XT and the XT/286 lines were phased out by late 1987 following the introduction of the IBM Personal System/2 series. The XT was directly succeeded by the 8086-based IBM PS/2 Model 30. Notably, while higher-tier PS/2 models adopted the Micro Channel bus technology, the Model 30 retained compatibility with the XT’s original 8-bit ISA bus slots.
Comparison Table
| Template:Verth | Template:Verth | Date Announced | Date Discontinued | Bus Architecture | Template:Verth | Template:Verth | Processor | Template:Verth | Template:Verth | Template:Verth | FDD | HDD | Notes | Ref(s). |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Template:Verth | Template:Verth | March 8, 1983 | June 19, 1984 | ISA, 8-bit |
8 | 2 | Intel 8088 | 4.77 | 128 KB | 640 KB | Single-sided, single-density (360 KB) | 10 MB | ||
| Template:Verth | Template:Verth | June 19, 1984 | June 30, 1987 | ISA, 8-bit |
8 | 2 | Intel 8088 | 4.77 | 256 KB | 640 KB | Single-sided, double-density (360 KB) | 10 MB |
(Note: For brevity and relevance to business contexts, only key entries highlighting significant product distinctions are included here. Complete details can be found in comprehensive IBM Personal Computer model listings.)
Reception
The XT garnered positive feedback, with the enhancements in PC DOS 2.0 regarded as a more impactful improvement than the modifications to the hardware itself. By the end of 1983, IBM had successfully sold every unit manufactured. Nevertheless, by 1985, the introduction of the IBM PC AT led to the XT becoming largely outdated for the majority of users.
See also
References
- Notes
- IBM (1983). Personal Computer Hardware Reference Library: Guide to Operations, Personal Computer XT. IBM Part Number 6936831.
External links
Photo collections: