The Olivetti PCS86

Hardware

The Olivetti PCS86 is a late-1980s XT clone. It's of similar spec to an IBM PS/2 Model 30 or an Amstrad 2086/3086.

The hardware includes:

640k RAM. There are also two SIMM sockets for extra RAM, which the computer can use as EMS memory.
CPU: NEC V30 at 8MHz.
Two 3.5" drive bays. The right-hand one holds a floppy drive; the left-hand one can hold a second floppy or a hard drive.
Three full-length 8-bit ISA slots, on a riser card.
Built-in floppy controller, which supports 1.4Mb floppy drives.
Built-in IDE controller. I suspect this is XTA rather than standard ATA.
Real-time clock (on my PCS86, the clock battery does not hold charge).
Integrated Paradise VGA chipset.

The following connectors are on the back panel:

PS/2 keyboard connector. This works with most standard PS/2 type keyboards.
PS/2 mouse connector.
Standard VGA connector.
Parallel and serial ports.

One curious feature of my PCS86 (and presumably of all single-drive models) is that it only has a single internal power connector - there's no way to power a second floppy drive or a hard drive.

The PCS86's BIOS is in a 64k ROM. All functionality is included in the one BIOS at 0xF0000; there is no separate VGA BIOS at 0xC0000 or hard drive BIOS at 0xC8000. There are two sets of video BIOS code - one to support the onboard VGA, and another to support a secondary CGA or MDA.

The BIOS claims (if you interrogate it with INT 0x15/AH=0xC0) to be for a PS/2 Model 30, submodel 109 (i.e. BIOS 1.09), revision 1.01. Most of the BIOS quirks found in earlier Olivetti PCs have gone, but video mode 0x40 (640x400x16) is still present. When this mode is selected, the CGA BIOS is used rather than the main VGA BIOS.

There are still a few traces of the master data table in the BIOS. When the VGA BIOS has control, the bytes at 0040:0084 are standard VGA/EGA variables (rows on screen, pixels per character, and video options). When the CGA BIOS is in use (either when the main screen is in mode 0x40, or when a secondary CGA is in use), 0040:0084 may contain a DWORD pointer to the master data table, which is used to locate the 8x8 and 8x16 bitmap fonts. The BIOS does not set up a master table; this would have to be done by a transient utility. When using the table, the BIOS (sometimes) checks if the first word is 16h. If it is, then it treats the table as valid; if not, it uses hardcoded ROM fonts. At other times, particularly in mode 40h, it uses the table without checking.

John Elliott 30 July 2004