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.
After numerous reliability issues in 1986 it was updated to the 1541C and matched the C64C in off-white colour, however it was unfortunately only slightly more reliable than its predecessor.
In 1988 the 1541C was replaced by the 1541-II. It boasting a greatly reduced form factor that is largely due to its external power supply vs. the internal transformer set up of previous models. Although redesigned, the 1541-II continued to make use of the lever drive release found to be reliable in the second and subsequent releases of the 1541.
Like the 1541/1541C the 1541-II 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 170k Bytes of capacity but the onboard operating system, 'CBM DOS 2.6', needs to allocate a small share for itself. The 170k Byte 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 is 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.
While the drive had been redesigned it was still slow, and yet to its credit was much quieter than the 1541 and 1541C models. The drive's main failing point was its new, external power supply brick that was totally encased in non-heat dissipating resin and was completely unserviceable.
If you ever had one of these drives that started to load a program and then stopped loading even though the disc kept spinning, it was probably the power brick that was at fault and not the drive.
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.
On the rear of the more recent drives are two paddle switches that were set in the up position by default designating the drive as device 8.
Both switches up = Device 8 (factory set)
Left switch down with right switch up = Device 9
Right switch down with left switch up = Device 10
Both switches down = Device 11