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Commodore PC10-III

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    Commodore PC10-III

    The Commodore PC10-III, PC20-III and Colt are IBM PC XT-compatible computers released by Commodore Business Machines in 1988. All three systems share the same motherboard with the main differences being disk capacity and minor cosmetic variations. Stickers on the motherboard and the back of the case sometimes identify these models as "10c".

    The majority of the major ICs and the hard drives used in these machines were manufactured by Western Digital, or its subsidiaries Paradise and Faraday. Further, the low level format routine which can be called from DEBUG in DOS identifies itself as being copyright Western Digital.


    • CPU: Intel 8088-1 running at 4.77MHz (Standard), 7.16Mhz (Turbo), or 9.54MHz (Double)
    • Optional 8087 math co-processor
    • RAM: 640KB
    • ROM: 32KB Phoenix Self-configuring BIOS (Versions 4.35 through 4.41 are known to exist)
    • Chipset: Faraday FE2010A single chip controller IC
    • Clock: Battery-backed Real Time Clock (RTC) maintains the date and time while the system is powered off
    • Floppy Drive: One or Two 360K 5.25-inch (720K 3.5-inch optional on PC20-III) (SMC FDC9268 controller)
    • Hard Drive: 20MB XTA (8-bit IDE) (standard on PC20-III)
    • Sound: On-board piezoelectric beeper
    • Ports:
      • 9-pin d-sub Bus Mouse port compatible with Commodore Amiga 1352 mouse (MOS 5720)
      • 25-pin d-sub RS-232 serial port (Western Digital WD8250-PL)
      • 25-pin d-sub 8-bit Centronics parallel port (Paradise PPC1)
      • Din-5 IBM PC XT-compatible keyboard port
      • 9-pin d-sub RGBI/Monochrome video port
      • RCA composite video port
    • Video: Onboard Paradise PVC4
      • MDA Monochrome Text
      • Hercules Monochrome Graphics
      • CGA Color Text and Graphics
      • Plantronics Colorplus Graphics
      • Alpha132 Monochrome Text
    • 3 8-bit ISA slots for expansion
    • 75 watt power supply

    Configuration and Upgrading

    All models come with the same speed CPU. Commodore PC 20-IIIs originally shipped with 20mb Western Digital hard drives. Some motherboards have the first 512k of RAM soldered with the remainder in sockets, suggesting that Commodore may have intended to offer these machines with only 512k from the factory. It is unclear if this ever happened.

    The 8088-1 CPU is capable of running at the "Standard" speed of 4.77MHz, a "Turbo" speed of 7.16MHz or "Double" speed at 9.54MHz.
    Processor Speed

    The computer always starts at 4.77MHz when first powered on. The speed can be changed either through pressing a combination of keys on the keyboard or by using the SPEED.EXE utility.

    Once the system has booted into DOS the following key combinations will change the CPU speed on-the-fly:
    • CTRL+ALT+S switches the CPU to the "Standard" 4.77MHz speed
    • CTRL+ALT+T switches the CPU to the "Turbo" 7.16MHz speed
    • CTRL+ALT+D switches the CPU to the "Double" 9.54MHz speed

    Processor Upgrade

    There are two types of processor-related upgrades that can be done to these systems. You can replace the CPU and/or add a math coprocessor.
    V20 CPU Upgrade

    A common upgrade for computers using the Intel 8088 CPU is to replace the chip with the NEC V20 CPU. The NEC V20 CPU is pin-compatible with the 8088 but enhancements in the internal design of the V20 allow it to perform 10-40% faster than the 8088 at the same clock speed. The V20 also adds additional processor instructions from the 80186/80286 family which allows some software written for those architectures to run on these systems.
    If you choose to add a V20 CPU to your system, make sure that you use a V20 chip with the "-10" suffix in its model number. This denotes a 10MHz-capable part. If you install a "-5" or "-8" version, your system will be limited to 4.77MHz "Standard" or 7.16MHz "Turbo" and will behave erratically if you attempt to run in 9.54MHz "Double" mode.
    To install a V20 CPU, simply lift the original CPU from its socket and replace it with the V20. No software is required.
    286 Accelerator

    Several companies produced 286 upgrade cards for 8086/8088 based PCs. Common models include the Orchid Tiny Turbo and the SOTA 286i. Virtually all operate the same way, with a card being installed in an ISA slot and a ribbon cable plugging into the CPU socket in place of the 8086/8088. A 286 CPU on the board then takes over, allowing the computer to operate much faster. Some models also allow a 287 math co-processor to be used, which can be significantly faster than the 8087. The original CPU can be placed in a socket on the card so that the user can switch back to it if they have a piece of software that does not work at the higher speeds. These cards should be fully compatible with the Commodore PC.
    Math Co-processor

    There is an empty socket on the motherboard for an Intel 8087 math co-processor. This chip allows for dramatic improvements in floating point math calculations for software applications written to take advantage of it. It is important that you use the 8087-1 model chip as this version is capable of running at the same speeds as the main CPU. If you get a different model, your system will behave erratically when you attempt to run the CPU at faster speeds.
    To install an 8087 math co-processor, simply insert the chip into the empty 8087 socket on the motherboard.

    All models appear to have shipped with 640K of RAM pre-installed. This is the maximum "base" memory which XT PCs can address, so there is no option to add additional RAM directly to the motherboard. To go beyond this you may use 8 bit ISA "Expanded Memory" (EMS) boards, such as the AST RAMPage PC. These will require additional software to be loaded before the memory will become usable. Be aware that not all software can use EMS.
    Hard Drives

    The PC20-III comes standard with a 20MB Western Digital XTA (8-bit IDE) hard drive pre-installed while the PC10-III and Colt have only floppy drives standard. When no hard drive is installed, even if the on-board interface has been disabled via JMP208, the BIOS will display "Hard disk not found" on startup.

    It is possible to add a hard drive to the PC10-III and Colt or to replace the hard drive in the PC20-III. There are two ways to add or replace a hard drive in these systems. You can either use the built-in XTA interface or use an add-in controller card. Using the on-board interface frees an ISA slot for additional expansion. Using an add-on card allows for significantly more models of hard drive to be used, and even multiple drives.
    Built-In XTA Interface

    The PC10-III/PC20-III/Colt is extremely limited in what hard drives it can support. As its ISA bus is only 8 bit, it cannot support a full 16 bit IDE interface. Instead it uses a short-lived 8 bit variant of IDE known as XT or XTA. Only a small number of hard drives were manufactured which supported this standard. If a drive does not explicitly state XT compatibility, then it most likely will not work.

    Further, the first BIOS revision (4.35) appears to be limited to drives under 20MB. If you use a drive larger than 20MB on an early BIOS, the system will see it as a 10MB drive. With the ST-351A/X, it is possible to set a jumper on the drive to force it into 20MB mode. While this has the unfortunate effect of cutting the drive's capacity in half, it's better than leaving it at the default settings and only getting 10MB. BIOS version 4.36 and above are able to see the ST-351A/X's full size.

    XTA compatible hard drives include:
    • Western Digital 93024, 93028, 93034, 93044, 93048 (20-40MB) (95xxx variants are the same as the 93xxxs, but mounted in 5.25" adapters) - VERY UNRELIABLE
    • Conner CP-2024XT (21MB)
    • Seagate ST-351A/X (43MB) (Can be jumpered for either AT or XT mode)
    • Seagate ST-325X (21MB)
    • Miniscribe 8450XT (42MB)

    Of these models, the ST-325X and ST-351A/X are probably the best choices. The ST-325X is ideal for machines with early BIOS chips. The ST-351A/X can give greater capacity in later systems, or be jumpered to 20mb for early machines. They are both quiet running and reliable. The Western Digital models should be avoided, despite being used in the 20-III from the factory, as they are highly unreliable.

    To install a hard drive on the internal IDE interface, it must be enabled by a jumper. PC 20-IIIs with factory hard drives should already have this jumper in the correct position. Other models will likely need the jumper moved. The jumper in question is located directly beside the floppy interface and marked JMP208. To enable the on-board interface, it must jump the two pins which are in line with the other jumper block beside it. To disable the onboard interface and allow the use of an ISA hard drive controller, it must be moved to jump the center and outer pin.

    Once a single compatible hard drive has been attached and the internal bus enabled, the drive will need to be set up with the built-in low level format tool. Observe upon booting the computer that the "Hard disk not found" message on the BIOS screen should have disappeared. If it remains, there is a problem with the drive or the way it has been attached. Confirm the jumper settings and the ribbon cable orientation. If the message is gone, proceed to the formatting stage.

    From MS-DOS, run DEBUG.EXE. At the - prompt type G=FA00:5 and press enter. You should now see the Western Digital IDE Superbios screen, which you can use to configure the hard drive. Press Enter to select the first hard drive, enter again to accept the interleave value, then choose if you will manually enter the drive parameters or not by select Y or N for dynamically configuring. Some drives will need manual values entered, while others will be automatically detected. If you are unsure, try selecting N the first time and allowing it to automatically set up the drive. At this point the program will ask you to press Y to begin format. If the drive is working and properly configured, the drive should now be configured and low level formatted.

    Once the system has rebooted, you may proceed to use FDISK and the DOS FORMAT commands to set the drive up as you would any other. Be aware that if you are using the factory MS-DOS 3.2 or similar, you will not be able to create a single partition larger than 32MB. Also be aware that you may need to instruct FDISK to make your primary partition active after you create it. If the partition has not been made active, it will not be bootable, though DOS will still be able to interact with it.
    Add-In Controller Card

    If you don't have an XTA-compatible hard drive or if you just want more storage, you can use an add-in hard drive controller card. There are a few options available for this:
    • MFM/RLL controllers are old, slow, low-capacity and unreliable
    • ESDI controllers are old, still-kind-of-slow, low-capacity and unreliable
    • SCSI controllers for 8-bit ISA are hard to find and expensive these days but will let you use most SCSI hard drives. The Seagate SCSI controllers ST01 and ST02 require BIOS 4.36 through 4.41 to work.
    • [wiki="XTIDE project"]The XT IDE Project[/wiki] here is an affordable way to get a lot of storage for very little money by allowing the use of standard 16-bit ATA/IDE drives in an XT system.

    When using any add-in card, you must make sure that the built-in XTA controller is disabled. This is done with jumper JMP208 on the motherboard. To disable the built-in XTA controller, set JMP208 so that pins 1-2 are bridged. JMP208 can be found right next to the connector where the floppy drive cable plugs into the motherboard.
    Floppy Drives

    Depending on the model and options, these computers came with one or two floppy drives. The first (Drive A was always a 360k 5.25" floppy drive. The second (Drive B could be another of the same, or a 720k 3.5" floppy drive. It is possible to upgrade a system by adding a second floppy drive, but the process differs slightly from more modern PCs.

    The floppy ribbon cable used in these machines lacks the twist between the end and the middle connector which modern PCs use to tell the drives apart. Instead, jumpers on the drives themselves are altered so that they may operate independently of each other. Drive A is set to DS0, while Drive B is set to DS1. Some early drives refer to the settings as DS1 and DS2, which can cause confusion. And not all drives will have selection jumpers visible on the outside.

    There are 3 options for connecting a mouse to your system. You can connect an ordinary serial mouse to the 25-pin RS-232 serial port, but since the PC10-III/PC20-III/Colt only have one serial port, the may be undesirable. You can use an add-in card such as a multi-IO or bus-mouse card but, again, this may be undesirable due to the fact that the system only has 3 ISA slots. The third option is to plug a Commodore 1352 mouse into the 9-pin Mouse port. The 1352 mouse is most often used with the Commodore Amiga line of computer systems, however, it is also compatible with several of Commodore's PC-compatible systems. When the 1352 mouse is plugged in, it appears to the system as a standard bus mouse and can be used with Microsoft's basic MOUSE.COM driver in DOS or with the built-in drivers in Windows.
    Operation and Software

    These systems are among the 100% compatible IBM PC clones. That means they will run virtually all software designed for a real IBM PC XT. This includes MS-DOS, games, office programs, etc. Versions of DOS up to 6.22 are fully compatible.
    The included operations manual has Commodore part #319964-02. The dealers service manual is part #314860-01.
    Bundled Software

    Two 360k 5.25" floppy disks were included with these systems. The first contained MS-DOS 3.2, the second held GW-BASIC and related files. Two custom utilities, SPEED.EXE and SETCLOCK.EXE are found on the DOS boot disk. The PC 20-III has this software loaded onto the hard drive.
    SPEED.EXE Utility

    The SPEED.EXE utility can be executed with an appropriate command line switch to set the CPU speed as follows:
    • SPEED.EXE -s switches the CPU to the "Standard" 4.77MHz speed
    • SPEED.EXE -t switches the CPU to the "Turbo" 7.16MHz speed
    • SPEED.EXE -d switches the CPU to the "Double" 9.54MHz speed

    It is common to put "SPEED.EXE -d" in your AUTOEXEC.BAT file to set the CPU to its fastest speed immediately after booting.
    SETCLOCK.EXE Utility

    The system includes a Real Time Clock on the motherboard which maintains the correct time while the system is powered off. Unlike modern computers which set this time automatically when the computer starts up, the RTC in the PC10-III/PC20-III/Colt must be explicitly queried for the time using the SETCLOCK.EXE utility.

    The SETCLOCK.EXE utility can be used to set the system clock by reading the date and time from the RTC or it can be used to take the current date and time from the system clock and write it to the RTC as follows:
    • SETCLOCK.EXE -r reads the current time and date from the RTC and sets the system clock accordingly
    • SETCLOCK.EXE -w writes the system clock's time and date to the RTC

    These tools may be downloaded from PC
    ROM Tools

    Like most XT clones, this machine does not have a CMOS setup program which can be invoked on startup to configure the machine. But it does have two programs stored in its ROM BIOS which can be accessed via debug.exe from DOS.
    • G=FA00:5 loads the Western Digital IDE Superbios hard drive tool
    • G=F000:0 loads COMMODORE 8088 Monitor


    There are 4 dip-switches on the back of the unit used to configure the on-board video adapter.
    • Switch 1 configures the character set - Up(Off) selects the USA/Europe Character Set and Down(On) selects the Scandinavian Character Set
    • Switch 2 configures the adapter for monochrome or color output - Up(Off) selects monochrome output and Down(On) selects color output
    • Switch 3 and 4 define the default video mode:
    • Switch 3 Up(Off) and Switch 4 Up(Off) sets the default video mode to Monochrome
    • Switch 3 Up(Off) and Switch 4 Down(On) sets the default video mode to 80 Column Color
    • Switch 3 Down(On) and Switch 4 Up(Off) sets the default video mode to 40 Column Color
    • Switch 3 Down(On) and Switch 4 Down(On) disables the on-board video adapter

    Video Modes

    The system emulates four different display adapters.

    The Computer Graphics Array or CGA standard on these systems supports the following modes:
    • 80 column text mode (8x8 pixel character cell) in 16 colors
    • 40 column text mode (8x8 pixel character cell) in 16 colors
    • 320x200 graphics mode in 4 colors
    • 640x200 graphics mode in monochrome (black & white)

    These modes can be displayed as digital RGBI through the 9-pin monitor connector or composite NTSC video output. The display timings are:
    • Vertical Frequency: 60Hz
    • Horizontal Frequency: 15.7KHz
    • Maximum Dot Clock: 14.318MHz

    Plantronics ColorPlus

    Plantronic ColorPlus is a superset of the CGA standard and allows for more simultaneous colors to be displayed in graphics modes when used with software written to take advantage of it. Here are the two additional modes supported:
    • 320x200 graphics mode in 16 colors
    • 640x200 graphics mode in 4 colors

    These modes can be displayed as digital RGBI through the 9-pin monitor connector or composite NTSC video output. The display timings are:
    • Vertical Frequency: 60Hz
    • Horizontal Frequency: 15.7KHz
    • Maximum Dot Clock: 14.318MHz


    The Monochrome Display Adapter is a high-quality text-only mode allowing 80 columns of text (9x14 pixel character cell) in monochrome (black & white) as TTL monochrome through the 9-pin monitor connector or composite PAL output. The display timings are:
    • Vertical Frequency: 50Hz
    • Horizontal Frequency: 18.432KHz
    • Maximum Dot Clock: 16.257MHz


    The Hercules emulation provides a 720x348 graphics mode in monochrome (black & white) as TTL monochrome through the 9-pin monitor connector or composite PAL output. The display timings are:
    • Vertical Frequency: 50Hz
    • Horizontal Frequency: 18.432KHz
    • Maximum Dot Clock: 16.257MHz


    Alpha132 is a high-quality text-only mode allowing 132 columns and 43 rows of text (8x8 pixel character cell) in monochrome (black & white) as TTL monochrome through the 9-pin monitor connector. The display timings are:
    • Vertical Frequency: 48.7Hz
    • Horizontal Frequency: 18.52KHz
    • Maximum Dot Clock: 24.000MHz

    Repair Info

    These machines are sturdy and generally reliable, but they do suffer some age related faults.
    Leaky Batteries

    The CMOS settings and clock data are maintained by a 3.6v Ni-Cad battery, the same style used by many pre-Pentium PCs. It is located at the front of the motherboard beneath the drive cage. In time these cells tend to leak, and when they do the electrolyte causes corrosion and damage to nearby circuits. If you haven't already, you should remove the original battery before it destroys the motherboard. Leaked electrolyte is significantly basic and can be neutralized with household vinegar.

    The machine can continue to operate without a clock battery so long as the user remembers to set the clock on boot. Replacement Ni-Cad batteries are available, as are sockets to install the more common lithium CR-2032 battery. In the latter case, however, it is vital that a Schottky diode or similar be installed between the battery socket and the motherboard, as otherwise the machine will attempt to charge the lithium cell with possibly explosive results.
    Power Supply

    The power supply Commodored used in this machines is a custom form factor. Despite this, the supplied voltages are standard. If you have a machine with a faulty power supply, it should be possible to run it from a standard AT unit.
    The pinout is as follows, looking down on the motherboard:
    • 1 Power Good (5V)
    • 2 -12V
    • 3 +12V
    • 4 GROUND
    • 5 GROUND
    • 6 +5V
    The Vintage Computer and Gaming Marketplace
    The Vintage Computer

    1. How can one select which display adapter is beeing emulated ? With the DIP switches ? I can not imagine how I would switch them to get an Alpha132 emulated.
    2. Don't you have any BIOS images ? I have bought two of these, but have no single good BIOS ROM.

    GREAT page anyway. Thanks.


      Archeocomp, it'd be better for you to post your question in the forums instead of the wiki.