IBM PC XT (5160)
 | |
| IBM Personal Computer XT (5160) | |
| Specifications | |
|---|---|
| Developer | IBM Entry Systems Division, Boca Raton |
| Manufacturer | IBM |
| Type | Desktop personal computer |
| Released | March 8, 1983 |
| Discontinued | April 1987 (XT 286 production ended late 1987) |
| CPU | Intel 8088 @ 4.77 MHz Optional Intel 8087 FPU |
| Memory | 128 KB – 640 KB on-board (depends on motherboard revision) |
| Storage | 10 MB or 20 MB MFM hard drive (Seagate ST-412 or ST-225); one or two 360 KB 5.25" floppy drives |
| Display | MDA + IBM 5151 or CGA + IBM 5153 (separate adapter card) |
| Sound | Internal PC speaker, driven by Intel 8253-5 timer channel 2 |
| Dimensions | 19.5" W × 16" D × 5.5" H (50 × 41 × 14 cm) |
| Weight | 32 lb (15 kg) |
| OS / Firmware | IBM PC DOS 2.0 – 3.20; PC/IX; SCO Xenix; IBM Cassette BASIC in ROM |
| Predecessor | IBM PC (5150) |
| Successor | IBM Personal Computer AT (5170); direct PS/2-era replacement was the IBM PS/2 Model 30 |
| Model no. | 5160 |
The IBM Personal Computer XT (model 5160, often shortened to PC/XT) is the second computer in the IBM PC line, released on March 8, 1983 and discontinued in April 1987 (with the related XT 286 5162 continuing into late 1987). The XT shares its Intel 8088 CPU and 8-bit ISA bus with the original 5150 and is fully software-compatible. The major differences from the 5150 are an increase in expansion slots from five to eight, a base RAM of at least 128 KB, a redesigned two-chip BIOS, an included Asynchronous Adapter (serial card), a 130 W power supply, and a built-in 10 MB hard drive (later 20 MB) on most submodels. The 5150's cassette port was removed.
IBM never officially expanded "XT" to a phrase; some press materials of the era expanded it as "eXtended Technology".
Architecture and Processor
The XT uses an Intel 8088 running at 4.77 MHz, the same CPU as the 5150. A second socket on the motherboard accepts an Intel 8087 floating-point coprocessor sold separately.
The support-chip family is the same as the 5150's:
- Intel 8259A — programmable interrupt controller.
- Intel 8237A-5 — DMA controller (also handles DRAM refresh).
- Intel 8253-5 — programmable interval timer (system tick, refresh trigger, speaker).
- Intel 8255A-5 — programmable peripheral interface (keyboard input, DIP-switch readback, speaker enable).
- Motorola MC6845 — CRT controller, on the MDA or CGA display adapter, not on the motherboard.
There is no battery-backed CMOS — hardware configuration is set through DIP switches on the motherboard.
Memory and ROM
The XT has two motherboard revisions, identified by silkscreen marking:
| Silkscreen marking | RAM banks | BIOS shipped | Notes |
|---|---|---|---|
| 64-256KB (early) | 4 × 64 KB | 11/08/82 | Also found in the IBM 5155 Portable PC. Can be modified to support 640 KB on-board (IBM-supported procedure). |
| 256-640KB (later) | 2 × 256 KB + 2 × 64 KB | 01/10/86 or 05/09/86 | Native support for 640 KB on-board. |
The XT motherboard carries the BIOS in two sockets (U18 and U19), unlike the 5150's single BIOS chip in U33. The U19 socket on early-revision boards also contains part of IBM Cassette BASIC; on later 1986-dated BIOSes, U19 is shared between BIOS and Cassette BASIC.
BIOS revisions
| Date | U18 / U19 part numbers | ROM type | Floppy support | Notes |
|---|---|---|---|---|
| 08/16/82 | U18=5000026, U19=5000027 | MK38000 / MK37000 mask ROM | 360 KB | Possibly never publicly released; very rare. |
| 11/08/82 | U18=1501512, U19=5000027 (or 6359116) | Mask ROM, varies | 360 KB, partial 720 KB support | Standard first-production BIOS. |
| 01/10/86 | U18=62X0851, U19=62X0854 (or U18=62X0852, U19=62X0853) | 27256 EPROM | 360 KB and 720 KB | Adds Enhanced Keyboard support and 1.2 MB drive code (HD floppy controller still required). |
| 05/09/86 | U18=62X0890, U19=68X4370 (or 59X7268 / 62X0819) | 27256 EPROM | 360 KB and 720 KB | Final XT BIOS. |
The 1986-dated BIOS revisions have two notable caveats: they may produce a specific symptom documented by minuszerodegrees.net, and they may not support an IBM 5161 expansion chassis.
On the 1982-dated BIOS revisions, chip U19 contains part of Cassette BASIC and is not critical to operation. If the POST detects a failed U19, it displays "F6000 ROM" but continues booting. On the 1986-dated BIOS revisions U19 also contains part of the BIOS, so a failed U19 produces a 'dead' motherboard.
Storage and Expansion
- Eight 8-bit ISA slots (compared to five on the 5150). The slots are at slightly narrower spacing than the 5150's, so some multi-board cards will not physically fit. Two slots (behind the hard drive cage) cannot accept full-length cards. Slot 8 has a special "slot 8 compatible" requirement — non-compatible cards in slot 8 generate an 1801 error at POST.
- Floppy disk drive — one or two 5.25" 360 KB full-height drives (Tandon TM100-2 or equivalent). Later submodels switched to half-height drives.
- Built-in hard drive — a 10 MB Seagate ST-412 with Xebec 1210 MFM controller was the standard configuration. Later submodels shipped with a 20 MB ST-225 half-height drive.
- No cassette port (removed from the 5150 design).
- Included Asynchronous Adapter — serial card with 8250 UART, standard on most submodels.
- Optional IBM 5161 Expansion Unit — adds eight more ISA slots and room for two more full-height drives, connected via an Extender Card in the host and a Receiver Card in the 5161.
Display
The XT has no on-board video; video is provided by an ISA adapter card driving a separate monitor:
- MDA + IBM 5151 for 80×25 monochrome text.
- CGA + IBM 5153 for text and graphics.
- From 1985, the EGA and the PGA became available as options.
Submodel 5160-788 was the only XT sold with CGA as standard equipment.
Keyboard
Most XTs shipped with the same IBM Model F (83-key) keyboard as the 5150, on a DIN-5 connector using the XT keyboard protocol. From 1986, submodels 268, 278, and 089 shipped with a 101-key Enhanced Keyboard variant (a Model M-style keyboard in a modified form that used the XT's keyboard protocol and lacked LEDs).
Power Supply
A 130 W power supply (compared to the 5150's 63.5 W / 130 W Type 1/2). XTs sold in the US were configured for 120 V only; international units shipped with switchable PSUs.
Submodels
The XT was sold in many submodels. The following table is from the IBM Personal Computer Family Service Information Manual (January 1989, SA38-0037-00).
| Submodel | On-board RAM | Floppy | Hard disk | Keyboard / notes |
|---|---|---|---|---|
| 5160-086 | 256 KB | 360 KB | 10 MB | |
| 5160-087 | 128 KB | 360 KB | 10 MB | |
| 5160-068 | 256 KB | 360 KB | none | |
| 5160-078 | 256 KB | 2 × 360 KB | none | |
| 5160-088 | 512 KB | 360 KB | 20 MB | Original Model F keyboard |
| 5160-089 | 512 KB | 360 KB | 20 MB | Enhanced (101-key) keyboard |
| 5160-267 | 256 KB | 360 KB | none | Original Model F keyboard |
| 5160-268 | 256 KB | 360 KB | none | Enhanced keyboard |
| 5160-277 | 256 KB | 2 × 360 KB | none | Original Model F keyboard |
| 5160-278 | 256 KB | 2 × 360 KB | none | Enhanced keyboard |
| 5160-788 | varies | 360 KB | 10 MB | CGA standard |
| 5160-568, -588, -589 | 256 KB | 360 KB | 0 or 10 MB | XT/370 — adds a System/370 co-processor board |
| 3270 PC (5271) | 256-384 KB | 360 KB | 0 or 10 MB | 3270 terminal emulation variant |
| 5162-286 (XT 286) | 640 KB | 1.2 MB HD | 20 MB | 6 MHz Intel 80286, 16-bit ISA, zero wait states |
General Maintenance
Cleaning procedures, PSU voltage checks, and preventive care for the XT are documented in IBM PC XT Maintenance Guide.
Troubleshooting
POST beep codes, parity errors, MFM hard drive faults and the XT-specific known problems (1801 slot-8 error, POST looping when SW1 bit 1 is ON, 1986-BIOS quirks) are documented in IBM PC XT Troubleshooting Guide.
Capacitor Replacement
The 5160 motherboard has 16 tantalum capacitors total: 13 on the +5 V line and 2 on the +12 V line (one of which is C56, a well-known short-circuit failure). The procedure and per-position photos are in IBM PC XT Capacitor Replacement Guide.
Gallery
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IBM 5160 PC XT -
Silkscreen marking for the early 64-256KB motherboard (minuszerodegrees.net) -
Silkscreen marking for the late 256-640KB motherboard (minuszerodegrees.net)
Related Pages
- IBM PC XT Maintenance Guide
- IBM PC XT Troubleshooting Guide
- IBM PC XT Capacitor Replacement Guide
- IBM PC (5150) — predecessor
- IBM 5161 Expansion Unit
- IBM Fixed Disk Adapter
- IBM Model F (83-key)
- IBM Monochrome Display Adapter / IBM Color Graphics Adapter
References
- IBM Personal Computer XT — Wikipedia. Source for the submodel list, dimensions (19.5 × 16 × 5.5 in), weight (32 lb / 15 kg), and the relationship to the 5161 and XT 286.
- IBM 5160 — Motherboard Versions, minuszerodegrees.net. Source for the 64-256KB / 256-640KB revision details.
- IBM 5160 — BIOS Revisions, minuszerodegrees.net. Source for the four BIOS revisions, IBM part numbers, and floppy support details.
- IBM PC-XT (1983) — DOS Days. Reference for original configuration and chronology.
- IBM, Personal Computer Family Service Information Manual (January 1989, document SA38-0037-00). Source for the submodel table.
- IBM, Personal Computer Hardware Reference Library: Guide to Operations, Personal Computer XT (Part number 6936831, 1983).