Commodore 64 Personal Computer Floppy Disc Drive - Dismantled for reference and curiosity
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 that 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 means it was easy for users to cut out a small, square notch 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 hole punch that aligned with the disc edge) were released for doing just this.
Each disc side technically has 170 kBytes of capacity, however the onboard operating system 'CBM DOS 2.6', needs to allocate a small share for itself. The 170 kByte capacity is broken down into 683 sectors on 35 tracks with each of the sectors holding 256 Bytes.
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 are set aside as a 'block pointer' to point to the next physical track and sector. So in actual fact a logical block of 256 Bytes only holds 254. This means that after formatting a disc, almost 165 kBytes out of the initial 170 kBytes was still available for use.
The drive is noisy, slow and with its internal power supply ran hot. That said, it 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 the mechanism made by 'Newtronics Co. LTD.' / 'Mitsumi Elect Co. LTD.' and features the more reliable lever release; see separate page in this section. The unit below is a Newtronics Co. LTD. / Mitsumi Co. LTD. model that can be easily confirmed by their sticker shown in image seventeen.
Changing Drive Number on the Hardware:
This is done most commonly to allow more than one drive to be chained to the same Commodore 64 computer.
Unlike the 1541 II that has two paddle switches on the rear, users need to cut one or two small jumper solder trails to make drive number changes to the 1541. These jumpers look like a solder disc with a line dividing them down the centre and only a thin link joining both sides across the middle. They're sometimes described a wide 'H' can be seen most clearly in the bottom left corner of image 11 marked J1 and J2. Note that sometimes they were labeled 1 and 2 or A and B. While there were a number of different boards manufactured and the jumpers may be located in different places, they always look similar and are always together. Both jumpers shipped with their links joined, designating the drive as device 8. To set the drive number choose one of the following combinations;
Both J1 and J2 joined = Device 8 (factory setting)
J1 cut with J2 joined = Device 9
J1 joined with J2 cut = Device 10
Both J1 and J2 cut = Device 11
To cut the jumper, carefully and completely scratch away the thin strip of metal joining the two sides of the H. If you need to change drive numbers regularly, a couple of switches could be added to the jumpers.