The IBM PC/XT (Model 5160) was IBM's second computer in the PC series, following the success of the [wiki="IBM 5150"]IBM PC[/wiki] (Model 5150).
The XT in IBM PC/XT stands for eXtended Technology and was introduced on March 8th, 1983.
The XT contained a few improvements over the 5150, including more expansion slots and native HDD support.
In 1984, the XT was overcut by the [wiki="IBM_5170"]IBM AT[/wiki] (Model 5170), and in 1987 it was replaced by the 8086-based PS/2 models.
[wiki="Image:5160.JPG"]thumb|right|The IBM 5160[/wiki]
BIOS and Motherboard Revisions

[wiki="File:PCXT PCBInfo early.JPG"]200px|thumb|rigth|The first revision[/wiki]
There were two versions of the XT. The first version ("early model") supported 256kB of memory on the motherboard itself and was expandable up to 640kb of RAM with the addition of an 8-bit ISA expansion card. Introduced in 1986, the second version ("late model") included the full 640KB of RAM on the motherboard itself and a revised BIOS that cut the boot time in half while adding support for enhanced keyboards.
There is however no significant difference in the layout of the actual system board. The difference is how it was configured. Even the first XTs could easily be made into 256-640KB systems just by adding a jumper, a multiplexer at U84, and replacing the BIOS (for full support with all the features of the "later model" XTs). However, there were actually two or three revisions of the PCB layout. The first revision (Raw-PCB number 1501490) has U90 left empty labeled as "SPARE", it has TD2 installed, and it also has two smaller components (a resistor and a capacitor) located above the speaker connector. The second revision has some re-arrangements of lines around U90, has TD2 replaced with a resistor in most of the cases, and has the two components moved to around E4. This change was introduced when submodel 086 replaced the submodel 087 in the spring of 1984. A third revision may also have been made, but the only difference to the second revision seems to be in one of the address lines going to the ROM BIOS, allowing only 32KB chips (instead of both 8KB and 32KB chips) to be used. This revision may have taken place with the introduction of the "late model" XTs in 1986.
Like the [wiki="IBM 5150"]IBM PC[/wiki] (Model 5150) the XT came with a [wiki]BASIC[/wiki] interpreter in ROM. The only ways to access this were:
  • Disconnecting the hard drive and leaving the floppy drive empty
  • Using the [wiki]BASICA[/wiki] program from a floppy (which included the extensions for using the disk drives)
  • Using a debugger to manually invoke a BIOS call.

Specifications and Upgrades

The standard 1983 XT included:
  • An Intel 8088 running at 4.77MHz (with a socket for an 8087 math coprocessor). AMD 8088 CPU's were also used in some models.
  • 128K of RAM, expandable to 640KB
  • Full height 5 1/4" double sided floppy drive capable of holding 360KB of data
  • 10MB Seagate ST-412 hard drive
  • an Asynchronous Adapter (serial card)
  • 130W Power Supply
  • Eight 8-bit expansion slots
  • PC-DOS Operating System 2.0
  • Monochrome [wiki]MDA[/wiki] video adapter options

The later models had 256KB RAM, half height floppy drives, an option for a 20Mb hard drive and an 'enhanced' keyboard (similar to a Model M). In 1985 IBM introduced a lower cost unit that was fitted with two full height floppy drives and had no hard drive.
Some after market upgrades included:
  • [wiki]CGA[/wiki] graphics card and monitor
  • [wiki]EGA[/wiki] graphics card and monitor
  • 256KB ISA ram expansion card

The 5160 today

In more recent years some enthusiasts have been able to add:
  • IDE hard drives and controllers (see [wiki]XTIDE project[/wiki])
  • ISA [wiki]VGA[/wiki] adapters (see [wiki]8bit Friendly ISA VGA cards[/wiki])
  • Ethernet LAN cards
  • 1.2MB 5 1/4" floppy drives
  • 1.44MB 3 1/2" floppy drives

Jumpers and adjustable components on the system board

Jumper Settings

There are a total of 5 sets of jumpers labeled E1-E5 on the system board, and one block of switches. In addition, there is an empty socket (U84, on 64-256KB boards) and a trimable capacitor.
  • E1 is handy if you have an Expansion card with a replacement BIOS in the F000:0000 segment
  • E2 is useful if you want to configure your 256 KB XT into a 640KB XT
  • E2 page 3, E3 and E4 are for compability with the Intel 2118, a seldom used 1x16Kb RAM chip
  • E5 is probably from IBM's initial tests

Note: On all motherboards some or all of these jumpers were not present, and in order to use them you would need to solder some pins to the motherboard. In addition, jumpers jumpered by default (except for E2) are hard-wiered, so they have to be disconnected before a jumper block is soldered on.
Switch Settings

Trouble Shooting

=== Beep Codes ===
  • No beep - Power supply, system board problem, disconnected CPU, disconnected speaker, or grounded keyboard data-line.
  • Continuous beep - Power supply, system board, or keyboard problem.
  • Repeating short beeps - Power supply or system board problem or keyboard.
  • 1 short beep - Normal POST - system is OK.
  • 2 short beeps - POST error - error code shown on screen.
  • 1 long, 1 short beep - System board problem.
  • 1 long, 2 short beeps - Display adapter problem (MDA, CGA).
  • 1 long, 3 short beeps - Enhanced Graphics Adapter (EGA).
  • 3 long beeps - 3270 keyboard card.

Further Reading

  • IBM PC/XT Technical Referance Manual

External Links:

  • [wiki]url][/url] The Vintage Computer Forums thread on the IBM 5160 BIOS revisions]