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Tom W. Durston's Custom Altair



MITS Engineering Machine, born 4 Mar 7
5

"DO NOT SHIP", Bill
(Bill Yates, MITS Head Engineer)






Tom W. Durston

The Altair 8800 mainframe shown here was used by me at MITS from 1975 though 1978 to develop and test Altair PCB designs and applications.


This unit has a unique engineering history at MITS, as I used it to develop the FDD controller, the FDD system, 88-ACR, 4K static board, and evaluate hundreds of enhancements, many of which were implemented in the 8800B.

 

This unit was also used for the very first test and debug of Bill Gates and Paul Allen's Altair Disk Basic and OS.  I couldn't go on Christmas Vacation until we found a way for software to check the disk 'data ready' flag and then read a data byte from the disk every 32 microseconds.  The Altair CPU wasn't fast enough to keep up with the disk data rate. We worked on a solution 24 hours per day until a fix was found. The ingenious solution was to input two bytes of data for each test of the  'disk data ready' flag.  I had Christmas a week late that year.

 

Tom Durston

MITS Product Development Engineer







April 27, 2017









Tom Durston's Custom Altair System

    Dual-drive custom FD360 Cabinet with Pertec FD400 Drives

    GW312 Serial to Ethernet Server (Supplemental Resource)

Internet Ready: The GW312 connects the Console and Communication RS-232 Serial Ports to an Ethernet network. The network can be LAN or Internet.

PC Ready: The serial ports can be accessed by Telnet or a terminal program on a PC. Windows PC Virtual COM drivers available for download.

A USB to RS232 adapter is also included.








Tom Durston's System includes a pair of external Pertec FD400 drives that can read original Altair diskettes.

The drive cabinet has been serviced and tested and works with the included disk controller pair. The drive cabinet also work with the FDC+ controller (not included). The drives are the same drives used in MITS Single drive cabinets.

Tom Durston's Custom Altair Mainframe



(Picture is Not current configuration) The Altair bus allows changing boards to form new configurations.
 
Tom Durston's Custom Altair System supports multiple configurations.

  • 64K for Altair Accounting Software
  • 60K for CP/M and 88-PMC & 4K Memory boards
  • Remote CP/M
  • Software, firmware, and boot disk available for soft-sectored Tarbell 1011D & Shugart drives (not included).


Dual-drive custom FD360 Cabinet
with Pertec FD400 Drives





Dual-drive custom FD360 Cabinet

The drive cabinet has been serviced and tested. Both drives work with the included disk controller pair. The drive cabinet also works with the FDC+ controller (not included).

The FD400 drives are the same drives used in MITS Single drive cabinets.

The two buffer boards inside are the latest MITS single-cabinet design. The buffer board power supply and huge heat sinks are not needed.

The power supply in the MITS single drive cabinets is prone to failure. The modular S-171 power supply in the FD360 cabinet is high quality. 

Provenance: This drive cabinet design marks the Alair's transition to modular power supplies for drive cabinets. MITS merger with iCOM resulted in MITS move to modular power supplies in the MITS/Pertec 3202 dual-drive cabinet.



MITS Single-Drive Cabinet and MITS/Pertec 3202 DualDrive Cabinet, not included.

All three drive cabinets were tested with the included MITS Controller pair. The controller pair was designed using this mainframe. MITS hard-sectored diskettes are interchangeable between all three cabinet types. 






Tom W. Durston's Custom Altair Mainframe




Tom W. Durston's 1975 mainframe with factory magic marker on the front panel.

Lighting can change darkness in a photo.






Note behind front panel dress plate.







MITS Engineering Machine born 4 Mar 75

"DO NOT SHIP", Bill
(Bill Yates, MITS Head Engineer)





The back panel is pre-diskette controller, probably 8800a. The bracket in the photo is the temporary solution used before the larger connector cutout. Newer back panels have a cutout for the 37-pin connector.






The back panel is pre-diskette controller. The bracket in the photo is the temporary solution used
before the larger 37-pin connector cutout.




Custom Front Panel Interface

Wires from the front panel connect to an S-100 connector. A short board connects to the front panel to the motherboard.

The board set pictured above does not match the current configuration.
The Altair bus allows changing boards to form new configurations.

Tom Durston's Custom Altair System supports multiple configurations.

  • 64K for Altair Accounting Software
  • 60K for CP/M and 88-PMC & 4K Memory boards
  • Remote CP/M

  • Software, firmware, and boot disk available for soft-sectored Tarbell 1011D & Shugart drives (not included).


Custom Front Panel Interface Connectors



Custom Front Panel connectors.

Older systems had the white wires connected directly to the motherboard. The 8800B has a special interface board. Tom Durston's mainframe has this one-of-a-kind removable interface.



Board Set Configurations


  • 64K for Altair Accounting Software
  • 60K for CP/M and 88-PMC & 4K Memory boards
  • Remote CP/M
 




"... many Altair hobbyists want to build up Rev 0 systems with all early MITS boards, the original low-wattage power supply, etc. These systems never existed in the real world! Tom Durston's system is a prime example -- upgraded bit by bit, improvements made along the way. "

Multiple configurations are available





Tom Durston's 88-2SIO





BAUD Rate switch added!

MITS Test Department board


Port 2 Wiring (RS-232 with CTS):
  • E1 Black to J3
  • E2 Red to I2
  • E3 Yellow to J1
  • E4 Green to N8
  • E5 Green to N6

  • S2-1 Red to I1
  • S2-2 Black to J4 to Ground
  • S2-2, S2-1 N.C. (CTS Enabled)
  • S2-3 Green to N7
  • S2-4 Black to S2-10
  • S2-5 N.C.
  • S2-6 N.C.
  • S2-7 Yellow to J2
  • S2-8 Green to N5
  • S2-9 N.C.
  • S2-10 Black to S2-4 to Ground




MITS Technician Bruce W Fowler (BWF or FOWLER on boards).



Tom Durston's Original IO Cables



Tom Durston's original 88-2SIO cables included. New cables are provided with the system.

Port 1, RS-232 lines 2,3,7 (Console)

S1-4 (Black) to DB25 (Pin 7)
S1-7 (Red) to DB25 (Pin 2)

S1-8 (White) to DB25 (Pin 3)

MITS software does not require handshaking. The Console can be a three-wire connection.

Port 2, RS-232 lines 2,3,4,5,7 (CTS for RCPM)

S1-4 (Black) to DB25 (Pin 7)
S1-7 (Red) to DB25 (Pin 2)
S1-8 (White) to DB25 (Pin 3)
S1-1(Brown) to DB25 (Pin 4)
S1-3(Green) to DB25 (Pin 5)
"Proper" internal cables depend on the application and may include board modifications including a current limiting resistor on 5V.

The original MITS 88-2SIO board requires modification to enable CTS or other handshaking signals.

MITS 88-2SIO Board.pdf



Tom Durston's Console cable



Tom Durston's Console cable

Two modern cables are included with a 9-pin connector for a PC, USB to serial converter, or Ethernet Serial Server.


Turnkey Module with 88-SYS-CLG Mod


A Turnkey Module was added to Tom Durston's System to allow all four 88-16MCS, 16K Static Memory boards to be used. The Altair Accounting Software requires a full 64K.

The Turnkey Module provides four 1702A PROMs for firmware.

Firmware is included for the UBMON monitor and DBL Disk Boot Loader. The board can be used with TURMON and other MITS PROMs.

The PROMs can be disabled to allow using a full 64K of RAM.
(88-SYS-CLG MOD).

The Turnkey Module provides auto-start logic to select the start address of the system.

The Turnkey Module provides a additional RS-232 Serial Port




The yellow green sticker was put there by former MITS Technician Steve Shepard. The white "Landmark" sticker indicates the board once belonged to Movie Inc., in Santa Fe, NM. Movie Inc merged with the Landmark Theaters in CA. Movie Inc. had a hard drive system and an 8800b computer with this Turnkey Module Installed. The computer was used to keep track of the complex movie business.





88-SYS-CLG Mod allows disabling PROMS to provide a full 64K RAM

Turnkey Module Notes

Turnkey Page



Tom Durston's 88-PMC  

48K-60K RAM Configuration

2K 1702A PROM board with ALTMON Monitor and DBL FDC Boot



14229 ENGR

Installing the 88-PMC requires removing the top 16K memory board to make addressing space available to PROMS. The DBL PROM boots the MITS Disk Controllers.



Mike Douglas has a great 1K monitor that is perfect for this board. The AltMon Altair Monitor adds function to a board that normally only has a boot PROM.

AltMon Altair Monitor

AltMon Command Summary:

     B boot disk by jumping to Altair disk boot loader (FF00)
     C SSSS FFFF CCCC compare blocks of memory
     D SSSS FFFF dump memory in hex and ASCII
     E SSSS FFFF DDDD exchange blocks of memory
     F SSSS FFFF DD DD find two byte sequence in memory
     G SSSS go to and execute
     H P load Intel hex file from 2SIO port 0 or 1
     I PP input from I/O port
     J SSSS go to and execute (G)
     K SSSS FFFF DD fill block of memory with “K”onstant
     L P load Intel hex file from 2SIO port 0 or 1
     M SSSS FFFF DDDD move block of memory
     N non destructive memory test (size RAM)
     O PP DD output to port
     P LLLL program memory (modify memory)
     Q SSSS FFFF compute checksum on range of memory
     R non destructive memory test (size RAM)
     S SSSS FFFF DD search for single byte in memory
     T SSSS FFFF test memory


MITS_Altair_88-PMC_PROM_Memory_Card_Manual.pdf


Disk Controller Board #1
MITS INC 1976 8800 BD 1  REV 0-X4









Disk Controller Board #2
MITS DISK #2 REV 0-X2








Tom Durston's Custom Mainframe was used to develop the MITS FDD controller and the FDD system!

This controller pair has been tested successfully with Tom Durston's drive cabinet and also tested
successfully with a MITS Single drive cabinet and a MITS dual-drive 3202.



CPU Connector





8800B CPU 
MITS 8800B CPU BD REV 0-X4





Note the resistor pack on the back of the 8800B CPU connector.





The star marks work of the MITS Technician Alan Haskins.



8800B Power Supply Board



The 8800B power supply board supports power hungry boards like the MITS 4K Static Memory board. 

Barely visable in the top corner is old repair for one connector to the 4-point bridge rectifier. A solder connection instead of a crimp connector.



Power Supply Filter Capacitors



Some Altair mainframes have a single large filter capacitor. This mainframe has two in parallel. Some people are afraid to turn on old hardware because old capacitors may leak, short, or otherwise fail. My experience, as of 2017, is that the big blue capacitors in Altairs still work.



 

One way to condition old capacitors is to use a Variac to bring up the line voltage slowly. Tom Durston sent me this design for another way to
condition old capacitors.



Here is the virtualaltair.com implementation of Tom Durston's design. The incandescent bulbs, 60W and 100W, are now vintage items. The idea works, but finding a 100W bulb will be hard over time. The incandescent bulb device was used on the mainframe (device not included).





Bottom view of the motherboard and the transformer tag





I found a tag that documents that the power transformer is a sample from the Heyboer Transformers company that made the 8800B transformer.



Mainframe Power Supply

For use with 120V 60Hz AC standard USA power only.

The 11/3/75 date indicates the mainframe power supply was upgraded
at least seven months after the mainframe was born.




The salesman sample transformer is bigger that the Attache transformer and smaller than an 8800B transformer.

TWD indicates the owner is Tom. W. Durston.

The orange switch is a fan on/off feature added by MITS Technician Alan Haskins.







Note the custom fan on/off switch and Velcro for the fan screen.



The tag provides some specifications for the transformer.



For use with 120V 60Hz AC standard USA power only.



Tom Durston's 16K Static Memory Boards
(four boards
)

Four original 88-16MCS Static Memory boards passed the MITS MTST Memory Diagnostic and are used with the MITS Turnkey Module to produce a 64K system.



MITS DIAG/MTST Memory Diagnostic - 64K No Errors






Note: S/N area and revision area after 200129







Note: Black Plastic RAM package
Note: BWF, FOWLER on back

The images above show Tom Durston's 16K Static Memory boards.

Two 16K boards are Copyright 1976 and two are Copyright 1977, (part 200129). The mainframe was born
4 Mar 75 and 16K RAM was added in the next two years.

MITS_Altair_88-16MCS_Static_RAM_Card_Manual.PDF


Tom Durston's 4K Static Memory Boards
(three boards
)

Three original 88-16MCS Static Memory boards can used with an 88-PMC to produce a 48K system with 2K of firmware.

Provenance: The 4K Static was designed using this mainframe. The 4K boards show marking that indicate the boards were used inside of MITS.

FOWLER - MITS Technician Ron Fowler
T & R - MITS Test & Repair
A.H. - Alan Haskins built this mainframe
ENG - MITS Engineering 





Test & Repair, Ron Fowler MITS Technician



A.H. - Alan Haskins, MITS Engineering



A.H. - Alan Haskins, MITS Engineering


AltMon "T" Memory Test
Top 12K No Errors, Three 4K Stat Memory Boards

 ALTMON 1.2

                                                                 

*TEST c000 efff ................................................................

................................................................................

................................................................................

................................................................................

................................................................................

................................................................................

................................................................................

................................................................................

................................................................................

................................................................................

................................................................................

......................


Note: Each dot is one pass of the memory test.


Altair Mainframe Case Top with duct tape
to alter cooling air flow





These images record tape placement for an Altair mainframe. Duct tape is common in MITS single drive cabinets to change air flow. The tape can be removed, however its use is part of Altair history.

Note: It is VERY IMPORTANT to install the top and screw it down tight, before shipping the mainframe. The top adds strength to the somewhat fragile outer case. The mass of the transformer can cause damage during shipment.



Boxer Fan Replacement



WS2107FL Boxer Fan 

The original fan is damaged (included).


A replacement Boxer Fan was installed to match the original configuration.


 



MITS Boxer fans have a green label . A replacement
WS2107FL Boxer Fan was installed to match the original configuration.






Back panel showing Velcro mounted fan screen, serial cables, and the fan on/off switch.



Mainframe Configurations