VIC-1540 disk drive

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The VIC-1540 floppy disk drive.
VIC-1540 box by Commodore Japan Ltd.

The VIC-1540 floppy disk drive (sold as the VC-1540 in Germany) is an external storage peripheral manufactured by Commodore specifically for the VIC-20 home computer. This was Commodore's first disk-drive designed primarily for the home market (PET computer perhipherals, while available to home users, were primarily marketed as a business product). The VIC-1540 can read and write to standard 5¼ inch double-density magnetic floppy disk media. The case of the VIC-1540 is modelled in white plastic with rounded corners to match that of the VIC-20.

The VIC-1540 connects to the VIC-20 through the standard Commodore IEC serial port present on both devices. The 1540 has two serial ports, thereby allowing other IEC devices (such as additional disk drives, printers or plotters) to be connected in daisy chain fashion. By factory default, this disk drive is set to be device number 8 on the serial bus, however this can be changed by opening the drive and connecting (or cutting) a pair of solder pads on the main circuit board. Many VIC-20 users mounted a switch on the face of 1540 disk drives which was connected to these pads - thereby enabling him or her to easily change the drive's device number (usually between device 8 and 9).

The VIC-1540 (like most disk drives for the Commodore 8-bit line of computers) was remarkable in that it had its own microprocessor (a 6502), RAM and built in CBM Disk Operating System (DOS). This meant that the VIC-1540 was really a simple computer. The advantage of this was that the DOS did not consume any of the VIC-20's RAM and that execution of disk commands did not belabour the VIC-20's own CPU. It also meant that the VIC-1540 was quite a flexible device that could be programmed by the user. However, these additional electronic components made the device quite expensive for the time. As a result, very few VIC-20 owners in the early 1980s had a disk drive - most choosing to use the much more affordable, but slower datassette tape drive.

The VIC-1540 was the precursor to the similar and very popular VIC-1541 disk drive. Externally, both drives look almost identical. However, close inspection will reveal the following differences.

  • The white plastic casing of the VIC-1540 is smooth while that of the VIC-1541 has a granular embossed texture.
  • The drive faceplate of the VIC-1540 is black, while that of the VIC-1541 is dark brown.
  • The label on the front of the VIC-1540 has a black background, while the VIC-1541's is dark brown.
  • It seems that on VIC-1540s the interior of the socket which accepts the power cord is white, while that of the VIC-1541 is black. However, at least one VC-1540 (German VIC-1540) has been seen with a black power socket, so it is possible that some VIC-1540s were also made with black power sockets. Since the power socket is an electrical component manufactured by a third-party, it may be that the colour changed over the manufacturing lifespan of the VIC-1540 while the specifications of the part remained the same.

The VIC-1540 is not entirely compatible with the Commodore 64 (and later) computers due to a timing error (which was fixed for the subsequent VIC-1541 drive). However, the VIC-1541 is otherwise electrically identical to the later 1541 and can be "upgraded" by replacing its ROMs so as to make it compatible with the C64 data transmission rates. After such an upgrade, true VIC-20 transmission rates can be reverted to with a software command. See the article on the VIC-1541 disk drive for more information.

VIC-1540 original English language manual.
The VIC-1540 beside the later VIC-1541. (NOTE: the 1540 has a user installed fan on top and a device number switch on the front.)
VIC-1540 with case open and metal RF shield removed.
Faceplate badge of the VC-1540 (German product name).
ROMs inside a VC-1540 (German product name). Image credit "Roelie"
Back of the VIC-1540 showing the white power socket.
Back of the (German) VC-1540 with a black power socket.