IBM XT 5160 (64-256KB)

Specifications

Notes

• POST cards do not work
• IBM 5160  -  Known Problems/Issues

Slot 8

On the IBM PC/XT, the eighth slot (closest to the power supply) is different from the others. Unlike the other seven slots, it is expected to respond with a 'card selected' signal whenever the card is selected. Basically, what this means is that cards inserted into this slot need to be 'Slot 8' compatible in order to guarantee 100% proper operation. Some cards won't work at all. It was designed to be used initially with the IBM Asynchronous Serial Card.

Memory

The maximum amount of memory supported by the IBM XT was 640 KB, achievable through the installation of 256 KB on the motherboard (using 64 Kbit DRAM chips). Later models allowed for all 640 KB to be installed directly on the motherboard. The remaining 384 KB of address space accessible by the Intel 8088 (between 640 KB and 1 MB) was used for the BIOS ROM, adapter ROM and video RAM space.

CPU

The Model 5160 came with the Intel 8088 microprocessor, which ran at 4.77 MHz. 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 math coprocessor could also be added for hardware floating-point arithmetic.

BIOS / RTC

The XT BIOS is in two separate chips on the motherboard. One is in socket U18 and the second is in socket U19. There were 4 revisions of the BIOS, differentiated only by date (no version number). Date formats are always MM/DD/YY. They were:

• IBM Part 5000026 (in U18) and 5000027 (in U19) - dated 08/16/82. Supports 360 KB floppy drives.
• IBM Part 1501512 (in U18) and 5000027 (in U19) or 1501512 (in U18) and 6359116 (in U19) - dated 11/08/82. Supports 360 KB floppy drives, with partial 720 KB support (requires DRIVER.SYS to be loaded using DEVICE=C:\DOS\DRIVER.SYS /D:0 /F:2 to successfully format a 720 KB disk).
• IBM Part 62X0851 (in U18) and 62X0854 (in U19) - dated 01/10/86. Supports 360 KB, 720 KB, and 1.2 MB floppy drives. Note that whilst 1.2 MB drives are supported by the BIOS, the supplied floppy controler in the XT does not support high-density drives.
• IBM Part 62X0890 (in U18) and 68X4370 (in U19) - dated 05/09/86. Sames as previous version, One known problem with this BIOS version is that some third-party floppy controllers fail to boot a known-good 1.44 MB floppy disk.

Just as with the original IBM PC, the XT did not come with a real-time clock onboard. Instead owners would need to purchase an expansion card that provided this convenience. Some memory expansion cards came with this.