commodore 128


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(click on picture)





               Above are the three screen modes of the Commodore 128                   
Click on screens for a larger view


Introduced January 1985
Release Price $299.99


      It was the beginning of a new year for Commodore Ltd. January of 1985 marked a full year since Jack Tramiel and the magic he brought with him had been gone from Commodore, the Plus /4, a computer that was to replace the aging C-64 was a flop. The people had spoken, they did not want a computer that was not compatible with the C-64's vast library of software and peripherals. But they did want advanced features that were on other computers such as the Apple IIe, the IBM PC, and it's clones and they wanted them at Commodore's usual affordable prices. 

      With this in mind, using the old Tramiel philosophy, Commodore pulled another proverbial 'rabbit from the hat' and introduced the Commodore 128 to the world at the winter CES in January 1985. It was everything the Commodorians were asking for and more. It had more RAM (128K expandable to 512K), it had an 80 column mode for word processing, it had a faster floppy drive, it could even run CP/M without any ad-on cards. It was completely compatible with the C-64 and it was priced under $300.

        The C-128 was in reality three computers built into one. This was achieved by designing a motherboard around the new MOS Technology  8502 8 bit processor, capable of emulating the older MOS Technology 6502/6510 processor, and the ZILOG Z80A 8 bit processor allowing them both to co-exist on the same bus sharing resources such as RAM and external peripherals. A remarkable achievement considering the timing problems that had to be overcome with the C-64's 6510 processor running at 1 MHz and the Z80A (which is an Intel 8080 clone) processor run at nearly two times that at 2 MHz. This all had to be incorporated into the same bus and output to the same peripherals. Commodore engineers did a masterful job of  creating a computer capable of running the vast library of CP/M based business software and easily switching to run the C-64 software complete with all of its great graphics and sound capabilities. 

         In its native mode the 128 has most of the capabilities of both the C-64 and the Z80A machine. In the C-128 mode it has access to 128K of RAM that is expandable to 512K. It also is capable of displaying 80 columns and the 1571 floppy drive is 7 to 10 ten times faster than the 1541. When the C-128 is in the CP/M mode the 1571 floppy drive is even faster running at up to 14 times the speed of the 1541 and since the 1571 is a double sided drive it has more than twice the storage capacity of its predecessor. Since the 128 uses the same VIC II 6564 video chip and SID 6581 sound chip it could access the C-64's graphic and sound capabilities which allows the game writers to take advantage of the extra memory which limited the C-64. Also exclusive to the C-128 mode is an extra 16K of RAM dedicated to video chip, bringing the total on board RAM to 144K.

      When the C-128 first boots up you are greeted with an entirely new screen (see the above screen shots) very much like the familiar dark blue on light blue of the C-64, only this one is black on green. You will also notice a newer version of BASIC has been loaded. The display proudly proclaims BASIC 7.0 is loaded and you have a whopping 122,365 bytes of RAM to work with. From this screen you can easily switch to the 64 mode by typing GO 64 and pressing the RETURN button. After a brief delay the familiar blue C-64 screen is displayed (see the above screen shots). The C-128 in the C-64 mode is 100% compatible with all of the C-64 software and hardware. 

      To accomplish this Commodore used the entire C-64 KERNAL and BASIC 2.0 ROM's unchanged, so when you GO 64 you are in effect shutting down the C-128 and turning on the C-64 instead of just running an emulation of the C-64. Since the keyboard of the C-128 is some what different from that of the C-64, only the keys that exist on the real C-64 are functional. The keys across the top of the 128 are only enabled for the 128 or CP/M modes. If the 1571 floppy drive is connected while you are in the C-64 mode it is automatically configured as the 1541 and will not read a double sided disk. Also there is no command such as the GO 64 to return the computer to the C-128 mode short of turning the computer off and rebooting. This was necessary to not make any changes to the original C-64 KERNAL to remain 100% compatible with the C-64 software and hardware.

      The C-128 case design is a radical change from the old boxy style of the C-64 or VIC-20. Although still a one piece design it is now sleeker and cream colored, a design that Commodore will use on all of its future one piece computers including the repackaged C-64C. On the right side of the case are 2 - 9 pin D-plug ports for connecting input devices such as joysticks, light pens, or a mouse. Next is a reset button and the off / on switch. Last is the power supply port, a 4 pin square plug for the rather large 'brick' power pack that supplies all the power for the computer. 

      There are 7 ports on the back from left to right, the first is a parallel expansion port for cartridges and special interfaces, next is a cassette port for the VIC-1530 Datassette, next is an 8 pin round DIN plug for the serial devices such as the floppy drives and printers, followed by another 8 pin DIN plug for a 40 column composite video output to a monitor like the Commodore 1802, next is a slide switch for the channel 3 / 4 output selection and an RCA type plug for the RF output to a standard TV,  next is a 9 pin D-plug for connecting to an RGBI (Red/Blue/Green/Intensity) monitor like the Commodore 1902, and last is a user port for devices such as the Commodore modem.

      The C-128 exhibited in this museum was added to the museum on May 20, 1999. It was purchased locally at a thrift shop.


System Architecture



Microprocessor 8502 / Z80A Standard on system board 128k
Clock speed 1 or 2 MHz / 2 MHz Maximum on system board 128k
Bus type CBM proprietary Maximum total memory 512k
Data bus width 8 - bits Memory speed and type 200ns dynamic RAM
Address bus width 16 - bits System board memory socket type 16 pin DIP
Interrupt levels N/A Number of memory module sockets 2 banks of 9 soldered
DMA channels N/A Memory used on system board TMS4164-20 (64k x 1 bit)

Standard Features


Disk Storage

ROM size 64k Internal disk and tape drive bays none
Optional math coprocessor no Standard floppy drives optional
Parallel port type no Optional floppy drives: up to 8
RS232C serial ports yes * 5 1/4 inch 160k single sided yes
Mouse ports yes / shared joystick * 5 1/4 inch 360k double sided yes
UART chip used N/A * 3 1/2 inch 800k yes
Maximum speed N/A * 3 1/2 inch 1.44MB no
CMOS real time clock no * 3 1/2 inch 2.88MB no
CMOS RAM no Hard disk controller included no

Video & Graphics



Graphics Processor VIC II 6564 / 8563 Sound Interface device SID 6581
Screen size - Col x Rows 40 / 80 x 25 Sound generation 3 voices
Resolution - Colors/High 16/320 x 200 ADSR capable yes
Resolution - Colors/Low      
Max colors 16 Programming language  
Sprites or Missiles 8 - 21 x 24 pixels Built in language CBM Microsoft BASIC 2.0 / 7.0
    Built in M L monitor yes

Expansion Slots


Keyboard Specs.

Total adapter slots 1 - 44 pin female edge Number of keys 92
Number of 8/16/32 bit slots 1/0/0 Upper/lower case yes/yes
    Keyboard cable length N/A

Physical Specs.


Environmental Specs.

* Height   Operating voltage @ 60 Hz 105-125 VAC
* Width   Maximum power supplied  
* Depth   Power supply output - volts +5VDC/+9VAC
* Weight   Power supply output - amps