Taken from Anatomy of the 1541 Disk Drive from 1984 Section 5.2
In the following table you find the technical data of al CBM disk drives compared. The Technical Data of all Commodore Disk Drives:
|DOS version(s) DrivesHeads per drive Storage capacity
Buffer storage (KB)
|Sectors per track||17-21||17-21||17-21||23-29||23-29|
|Bytes per block||256||256||256||256||256|
|Directory and BAM||18||18||18||38/39||38/39|
|Transfer rate (KB/s)internal||40||40||40||40||40|
|over ser./IEEE bus||0.4||1.8||1.8||1.8||1.8|
|Access time (ms)Track to track||30||30||30||5||5|
Overview of the “large” CBM drives
The VIC 1541 disk drive has the smallest storage capacity of the CBM disks, but it is also the only drive that can be connected directly to the Commodore 64 and VIC 20 over the serial bus.
The functions, construction, and operation are identical to those of the CBM 2031 drive. The only difference from the VIC 1541 is the parallel IEEE bus instead of the serial bus.
This results in an increase in the transfer rate to the computer of a factor of 5. To connect a Commodore 64 or VIC 20, one needs an IEEE interface, as with all other CBM drives. The storage format of the 2031 is compatible to the 1541; both have 170K per disk. Diskettes can be written with one device and read with the other. This is true for the next drive in the line, the CBM 4040. The 4040 is a double drive with 170K per drive.
The advantage of a double drive lies not only in the increased storage capacity, but also in the ability to transfer data from drive to drive. It is possible to copy complete programs and files using the existing 1541 command. OPEN 1,8,15, “C1:TEST=0:TEST” COPY -TEST-,D0 TO “TEST”,D1 copies the file TEST from drive 0 to drive 1 with the same name. In this manner one can concatenate several files on different drives. The most important capability of double drives is the ability to duplicate entire diskettes. This is accomplished by a command from the computer; the drive automatically formats the disk and then makes a track by track copy from one drive to the other. The command to do this is worded:
OPEN 1,8,15, “D1=0” of BACKUP D0 TO D1
The process takes less than 3 minutes on the 4040; during this time the computer may be used since the disk drive performs the entire operation by itself.
The two other CBM drives, the CBM 8050 and the CBM 8250 operate in double density (77 tracks). Disks written with the 1541 or 4040 are not compatible with the 8050/8250. Programs and data can be copied with the COPY/ALL program, which transfers from one format to another. This is the reason these drives have greater storage capacity: 1 MB for the 8050 and 2 NB for the 8250. The doubled capacity of the 8250 comes about because both sides of the disk are used (double-sided); it has two reads/write heads per drive. In order to be able to use the whole capacity for relative files (see section 3.4), a so-called ‘super side-sector’ was introduced, which contains pointers to 127 groups of 6 side sector blocks each. Through this, a relative file can (theoretically) hold 23 NB of data. These drives can be connected to a Commodore 64 or VIC 20 over an IEEE bus, so that these computers can also access several megabytes.
An additional advantage of the large CBM drives is their larger buffer storage. It is possible to have more files open simultaneously than on the VIC 1541. Up to 5 sequential files or 3 relative files may open at any one time.