SSE HardBox Corvus Interface

  • The HardBox from Small Systems Engineering Ltd is an interface box that connects a Corvus hard drive to a Commodore PET/CBM computer. It makes the Corvus appear as a CBM DOS device and supports all of the commands that a Commodore floppy drive does, with the exception of the memory access commands (M-R, M-W, M-E).


    The HardBox uses the same Z80-based hardware as the SoftBox only in a slightly different PCB configuration. See the SoftBox page for the schematic. The configuration differences are as follows:

    • ROM: the SoftBox has 4K of ROM stored in two 2716 EPROMs, while the HardBox has 8K of ROM stored in two 2532 or 2732 EPROMs. Wire straps select which type of EPROM is used.
    • RAM: either 4516 (16Kx1) or 4164 (64Kx1) DRAMs may be installed. They are pin compatible so no changes are needed to select the type. The HardBox normally has 4516s installed but will also work with 4164s. The SoftBox requires 4164s.
    • RS-232: the SoftBox may optionally have RS-232 components populated (8251 USART, COM8116 baud rate generator, 1488/1489 line drivers, 12V power supply). These will not be populated on the HardBox.
    • Transistor: some HardBox units found have a diode installed at TR2, others have a 2N2222A transistor. The SoftBox requires a transistor to be installed at TR2.
    • DIP switches: an 8-position DIP switch is sometimes populated on the SoftBox but is not used by the SoftBox firmware. The DIP switch is always populated on the HardBox and is used to select the IEEE-488 address and user area number.

    I have successfully converted a HardBox into a SoftBox.


    Note: Two sets of EPROMs were found marked only “295” and “296” but they have different contents. The version numbers listed are the ROM version reported by the HardBox diagnostics program.

    hardbox-295-2.3-ic3.bin – Socket IC3. Sticker “295”, Version 2.3.
    hardbox-296-2.3-ic4.bin – Socket IC4. Sticker “296”, Version 2.3.

    hardbox-289-2.4-ic3.bin – Socket IC3. Sticker “289”, Version 2.4.
    hardbox-290-2.4-ic4.bin – Socket IC4. Sticker “290”, Version 2.4.

    hardbox-295-3.1-ic3.bin – Socket IC3. Sticker “295”, Version 3.1.
    hardbox-296-3.1-ic4.bin – Socket IC4. Sticker “296”, Version 3.1.


    These disks have the same contents:

    HardBox Utilities (D80) – 8050 format
    HardBox Utilities (D64) – 4040 format


    hardbox-manual-rev2.pdf – HardBox manual in PDF format.

    SoftBox Conversion

    The HardBox is not useful without a Corvus hard drive to attach to it. However, it can be converted to a SoftBox, allowing you to run CP/M on your PET/CBM.

    Differences Outlined – The outlined areas to show what must be changed to convert the board from a HardBox to a SoftBox. At top left, an NPN transistor must be installed if the HardBox has a diode. The other areas are wire straps that must be changed. The DRAM sockets in a HardBox normally have 4516 (16Kx1) but may have 4164 (64Kx1). For the SoftBox, 4164s must be installed. Finally, the two 2532 or 2732 EPROMs for the HardBox must be replaced with the two 2716 EPROMs for the SoftBox.

    Transistor Orientation – A diode may be installed in TR2 instead of a transistor. If this is the case, the diode needs to be replaced with a transistor (2N222A or equivalent). Some boards do not have silkscreen. This photo is provided to show the correct orientation.

    Configured for SoftBox – I have replaced the wire straps with jumper blocks. This photo shows the correct configuration for using the board as a SoftBox.

    The EPROM images and CP/M boot disk can be found on the SoftBox page.


    Advertisement (Commodore Computing Intl, Sep 1983)
    Advertisement (Commodore Computing Intl, Feb 1984)
    Advertisement (Commodore Computing Intl, Nov 1984)


    This page would not have been possible without Anders Carlsson. Anders dumped the EPROMs, scanned the manual, imaged the disk, and even gave me a HardBox unit.