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08/26/10  Hit Counter

(Frequently Asked Questions)

Many questions have been asked regarding the new IMSAI Series Two Advanced Microcomputer System.  This web page will attempt to provide answers to some of the more common questions.  I f you can't find the answer your looking for here, please e-mail your question to

IMSAI Series Two Advanced Microcomputer FAQs

(h) indicates answers provided by Howard Harte; (t) indicates answers provided by Thomas "Todd" Fischer; no notation indicates an edited reply from both

bulletI don't recognize or remember an "ATX" motherboard. Can you jog my memory and explain what that is and what it's used for?

(t)  ATX is a specification for general PC system motherboard mechanical design and features that is adhered to by the majority of PC manufacturers today.  An "ATX" motherboard varies in size from the microATX form factor (9.6" x 9.6"), the Mini-ATX form factor (11.2" x 8.2"), and the full size ATX form factor (12" x 9.6").  What we're essentially saying is that you can have a modern PC contained inside the same IMSAI Series Two enclosure, which can accommodate any of the three.

bulletHas anyone connected a standard 3  1/2" floppy drive to your system (is it possible)? That would greatly enable software transfers.

(t)  The answer is "yes".  The "Super I/O chip used on the IMSAI Series Two MPU-C interface board contains a 2.88MB floppy disk controller (765B core), and supports two 5.25" or 8" single/ double density floppy disk drives.  Format of tracks, sectors, density, and side-select is software-selectable, and a format utility is provided as part of the software support package.

When you say "fully-loaded", what features/boards are you including?

(t)  The answer to this can be found at

I wasn't certain from reading whether this a kit or fully-built system.
(t)  The IMSAI Series Two system is fully assembled and tested, and carries a two-year no-hassle warranty.
What software and manuals are still available and/or provided with the system and in what format?
(t)  The IMSAI Series Two User Manual contains all the technical descriptions, theory of operation, schematics, and source listings for firmware and PLD's used with the system.  A companion CD-ROM contains Zilog Z8S180-oriented development tools, bridge software, and additional device technical information (PDF files) to provide as complete a reference and support package as we can.
bulletDoes the IMSAI Series Two have a monitor, boot program, utilities or way to read /write disks?

Yes.  A fully functional CP/M 3.0 BIOS is provided (with source code), along with the default bootstrap loader in FLASH EEPROM (again, with source code).  Since our original CP/M license with Digital Research presumably expired with the demise of the original firm, licensing rights are a question and we are not able to directly offer a full CP/M package , but we will provide links to download sites where you can "plug in" the rest of the required code and utilities.  In short, you can have a fully operational CP/M or ZS-DOS system with what we can provide.  BIOS, editing, compiling, and other development utilities are included in our software support package.
bulletDo you have a bios for the unit? Or ready to go CPM or Z system disks ready to boot?

(t)  Yes.  We provide the tailored code necessary to implement CP/M (and ZS-DOS, soon), and provide links to that code that we're not specifically licensed to supply.  However, the code is available for individual use for free on the internet.  We will provide the links to those sites that archive the code.  See the above answer.
bulletWhile I have all the CPM, Z stuff, I will need a way to edit the bios, build a system, what do you provide to get this going?

  Again, besides the development utilities that we provide on our software support package, links to many of the available archive sites for utilities and programs will be provided in the user software available to all purchasers of the new IMSAI Series Two machines.
bulletWhat size / type hard drives does it support, driver code for controller included?
(h)  Any ATA/IDE hard drive will work with the Series Two.  These drives must support PIO (programmed I/O) mode.  Ultra DMA is not supported.  As far as I know, all Ultra DMA drives also support PIO as well.  CP/M in general cannot support "large" drives.  For CP/M 2.2, I believe 8Mb is the max partition size (possibly 32).  CP/M 3.0 can support larger drives; however there is a performance impact (slower) for larger drives.  In practice, 8Mb seems like a nice compromise between size and performance.  I feel that we can achieve decent performance on the Series Two with 32Mb partitions.  Since CP/M supports 16 logical drives, that means that we can partition a single hard drive into many 8Mb (or 32Mb) drives.  In the future, I would like to add support for mounting and dismounting logical partitions (like in UNIX.)  At present, the best drives to use with the Series Two are probably around 1GB in size, as these are fairly common, low cost, and reliable.  In practice, it would be unlikely that the entire 1GB could be utilized effectively.  This would be 125 8Mb partitions, or 31 32Mb partitions.
I am very interested in the utility that lets me read from a connected ATX board. What OS (dos, win 9x, nt, 2000, etc.) does it need to run? Is it a loadable that runs in background?

  See the answer below
I was told that there is a way to install a CP/M image into an S-100 Ramdisk from my current Pentium III system. I have Windows 98, Linux, and a few other OSs sharing a hard disk. I have no idea how to get an image sent to another motherboard Ramdisk with a cable connecting the two boards.  Is it really possible?
(h)  What we are shooting for is an "application" that runs under Windows (or Linux, etc.) that allows the Series Two to use resources from the PC.  On the Series Two side, the CBIOS accesses a port (serial or parallel) and treats this port as a disk drive.  The CBIOS routines can emulate any standard drive (floppy, hard drive, etc) with the appropriate Disk Parameter Blocks (DPBs) and matching configuration on the PC side.
This allows the Series Two to access the PC's A: drive as if it was a native 1.44M Floppy Drive under CP/M.  In addition, the Series Two can access files on the PC's hard drive and sees them as a native hard drive.  Initially, the files on the PC side must be put into an "image" of a hard drive that the Series Two would recognize.  This is actually an 8MB file on the PC.  The Series Two performs seeks on this file as if it were a real hard drive.  We will provide utilities to insert and extract files from this image. 
In the future, we hope to be able to do this dynamically by allowing the Series Two to utilize a regular directory on the PC.  Every time a file is added to, or deleted from this directory, this would cause a "Disk Change" to occur on the Series Two end, which will cause CP/M to re-read the FCB (like a FAT for CP/M).  The application running on the PC which acts like a "server" would re-create this FCB for the Series Two.
bulletYou mention "I/O - the second of the 2 board set".  Is that part of the system?

The short answer is "Yes"!  Our original intent was for a single board solution providing memory, I/O, and interface circuitry that would utilize surface-mount components for all internal bus needs, and through-hole and socketed components for everything that saw the S-100 bus and external interface.  This was designed to allow the user a more friendly hardware environment that would make troubleshooting and board repair relatively easy, not requiring exotic repair procedures.  Unfortunately, the amount of board area required exceeded that available on the given surface area of a standard S-100 circuit card, and rather than try to cram everything on both sides of one board, we opted to split the functions into two distinct boards; the microprocessor and memory, and the I/O and interface.

This design change, while sacrificing yet another S-100 socket, allows the user to utilize either board independently or as a pair.  Each has it's own Lattice Semiconductor ispLSI 2000E CPLD which is a reprogrammable logic device configured to provide the majority of interconnect "glue logic".  Use of programmable logic devices allows the user to reconfigure the board resources for specific applications and unique requirements.  We provide full source code and user guides to assist in changes to the board architecture and I/O.
bulletI'm confused about connecting the IMSAI Series Two to a PC.  Do I have to install more hardware to make this work?

The PC that is connected to the Series Two may be an ATX-style motherboard optionally installed inside the chassis of the Series Two, or it can be a completely separate machine.  This makes no difference to the Series Two.  The physical connection can be made through the parallel (printer) port on the PC or a serial port, at the user's discretion requiring only a link cable (provided with all IMSAI Series Two systems).
I need some help in getting a connection to a PC and a means to xfer programs and files to back and forth to the Z system. Your parallel / serial link sounds like the perfect solution.

  Since there were many 8-inch formats, you will need to know the format of your Tarbell disks in order to write custom disk parameter blocks (DPBs) to support your old disks.  Also, are they single or double density?  Transferring your old files will require some amount of work in either getting your Tarbell controller working in the Series Two, or getting your old machine running and transferring the files over a serial link.
bulletThe old s100 boards had on-board regulators and higher voltage needs than the switching ATX supplies... is that provided?
The Series Two S-100 bus conforms to the IEEE-696 spec, and the MPU-C and I/O board included with the system also contain on-board regulators.  The Series Two chassis includes a step-up DC-DC converter to generate the +8 and +/-16 volts required for the S-100 bus.
bulletHow hard is it to rewrite the flash EEPROM to add monitor functions or firmware?
(h)  The FLASH can be programmed in-system.  There is a small utility that erases and reprograms the FLASH.  A copy of the source code for the current version of this utility is on my web site:  To use this utility, you load the code that you want burned into the FLASH into RAM using DDT or SID or ZSID and then run "flashpro" which detects the FLASH type and runs the programming algorithm.  I plan to make this program more user-friendly by allowing the user to specify the file to write, so that they don't have to do the loading with a debugger first. 
bulletThe older S100 boards only had 16 bit addressing.  While I don't expect to put them in banks, what problems will there be?
(h)  Many old S-100 boards only decode 16-bits of addressing.  This will cause a problem if you want to run an old board that uses memory mapped I/O or contains its own RAM or ROM.  There is a solution for this where you can punch "holes" in the address space in the lower 64K for these boards and then only generate the MWRT and sMEMR signals on the bus for CPU-generated addresses that are in the lower 64K.  This is possible by reprogramming the Lattice CPLD which does all of the glue/decode logic on the MPU-C.  This is not trivial; however, I may make some example CPLD code that shows how to do this.  I will definitely do it myself, because I want to use a Northstar MDS floppy controller with the system, and this card uses memory mapped I/O from E800h-EBFFh. 
Another solution is to add some decoding logic to each adapter board that decodes the upper 4-bits.  This may be the most versatile solution, as you can then keep "Bank 0" as a solid 64K RAM bank, and locate your controllers in some of the upper banks where they will be out of the way of the BDOS, CBIOS, etc. 
bulletWill a memory mapped video card work.
Yes.  We are considering a design for an advanced video controller, and that is a project that we may undertake in the future when the Series Two itself is in production, depending on demand.
bulletIs Phantom signal supported?
(h)  Yes, and as a matter of fact, it is required for the MPU-C power-on jump circuit.
Will I need to check each board for the latest standards to work on the newest IEEE-696 S100 standard?

  The S-100 bus has always had "problems" in that different manufacturers used some of the signals for different purposes.  We are adhering to the IEEE-696 spec as close as possible; however, the original front-panel signals are still on the backplane (RUN, SS, XRDY, etc).  I have provided jumpers on the MPU-C to enable/disable these signals, so that complete IEEE-696 compliance can be met.  In addition, I have provided test points for the NDEF/RFU lines (which used to be PROT, etc) and jumpers for the additional grounds specified by the 696 spec. 
I don't have 22nice and I think Sydex is gone.  Is it still available somewhere?

(h)  One of many available download sites is  I have my Northstar Horizon running on the Internet, you can access it at  It is much slower than the Series Two and lacks a front panel. However, much of the CBIOS and I/O subsystem that I designed for this machine are similar to the Series Two. Source code for it are also available on the link with the FLASH programming code.  As an exercise, you can try the Horizon out, and see how fast it is loading programs, etc.  This is due to the IDE disk controller.  The CPU board is running at 6MHz.  You can compare that with the Cromemco also on my site, which uses 1.2M 5.25" floppy drives as 8" replacements... much slower!
The Horizon takes about 10 seconds to boot because it's on a power controller.  The power is applied when a telnet connection is made to the system.  The hard drive takes about 10-seconds to spin up.  If I simply reset this machine, it boots in about one second.  The entire BDOS and CBIOS is in FLASH, and the CCP is loaded from the hard drive. 
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