Commodore 1541 Floppy Drive Newtronics / Mitsumi Japan Rev A

The Commodore 1541 Floppy Drive (AKA VIC-1541 / AKA CBM 1541) is a single sided, 5 1/4" floppy disc drive released for use with the Commodore 64 which followed in the footsteps of the 1540 released for the VIC-20.

The 1541 Floppy Drive did not have a sector hole sensor and so was 'soft sectored'. This meant that it was easy for users to cut out a small, square hole on the other edge of a floppy disc to allow both sides to be used. Many cheap, third party 'disc double-siders' (basically a square hold punch that aligned with the disc edge) were released for doing just this.

Each disc side technically had 170kBytes of capacity but the onboard operating system, 'CBM DOS 2.6', needed to allocate a small share for itself. The 170kByte capacity is broken down into 683 sectors on 35 tracks with each of the sectors holding 256Bytes.

CBM DOS 2.6 used a BAM ('Block Allocation Map') and one track was used for that. On top of that, out of each physical sector two Bytes were set aside as a 'block pointer' to point to the next physical track and sector. So in actual fact, a logical block of 256Bytes only held 254. This meant that after formatting almost 165kBytes out of the initial 170kBytes was available for use.

The drive was noisy, slow and with its internal power supply ran hot but is sure beat waited for tapes to load.

There are two main versions of the 1541 Floppy Drive and both are easy to spot. The first has a drive mechanism made by 'ALPS Electric Co. LTD.' and can be identified by the push in, spring loaded disc release*.
The second had their mechanism made by 'Newtronics Co. LTD.' / 'Mitsumi Elect Co. LTD.' and had the more reliable lever release**.

*See separate page on this site for details on this version.

**The unit below is a Newtronics Co. LTD. / Mitsumi Co. LTD. model which can be easily confirmed by their stamping seen in image seventeen.

Common Commands:

LOAD"$",8 (loads the directory of the disc to BASIC RAM and displays it on screen)
LOAD"*",8,1 (loads the first program on the disc OR the last program loaded)
LOAD"PROGRAM NAME",8,1

In these examples ,8 states which device to use and ,1 indicates that the program should not be loaded into BASIC RAM but to the memory address specified by the program's header. The 1 usually indicates a machine code / machine language program.

Changing Drive Number on the Hardware

This was done most commonly to allow more than one drive to be chained to the same Commodore 64.

Unlike the 1541 II which has two paddle switches on the rear, users needed to cut one or two small jumper sloder trails to make the changes on the 1541.

These jumpers look like wide 'H' symbols and can be seen most clearly in image 11 listed as J1 and J2; note that sometimes they were labelled 1 and 2 or A and B. There were a number of different boards manufactured, whowever the jumpers will look the same, even if they are located in a different place.

Both H shaped jumpers shipped linked which designated the drive as device 8. To change the drive number choose one of the following combinations. To cut the jumper, carefully and completely scratch away the thin strip joining the two sides of the H.

J1 cut with J2 linked = Device 9
J1 linked with J2 cut = Device 10
Both J1 and J2 cut = Device 11

If you need to change drive numbers regularly, a couple of switches could be added to the jumpers.

Commodore 1541 Floppy Drive
Commodore 1541 Floppy Drive Motherboard
Commodore 1541 Floppy Drive PCB
Commodore 1541 Floppy Drive Head
Commodore 1541 Floppy Drive Motor Commodore 1541 Floppy Drive Protector      
 
Unit pictured has been sold and its location is unknown.