The Commodore 1581 was developed as a replacement for the older 5,25" disk drives (1541, 1571). It utilizes a 3,5" disk, which when formatted provides 800k of storage (vs. 169984 bytes available on the 1541 and 349696 bytes for the 1571).
Other improvements include faster access times, the ability to make partitions, an external power supply (reduces heat buildup), etc.
The following specifications is from the 1581 service manual.
* 3.5 inch, +800K storage * Increased buffers, fixed BAM locations * Expanded controller commands * Track cache buffer * Configurable auto boot file * User alterable physical/logical track and sector translation * Fully vectored jump table * Partition capabilities * Wild card enhancements * Standard, fast and burst serial capabilities * Expanded burst command set
2. HARDWARE SUMMARY
PROCESSOR: 6502A, WD1770 ROM: 32K RAM: 8K I/O: 8520A
GROSS DATA ORGANIZATION: o 3.5 Inch Disk o Double-Sided o 80 Cylinders/160 Tracks
PER TRACK ORGANIZATION: Hex 4E written as a gap, with 10 sectors of data, with full gaps written for motor speed variation.
PER SECTOR ORGANIZATION: MFM Encoding 12 Bytes of Hex 00 3 Bytes of Hex A1 (Data Hex A1, Clock Hex 0A) 1 Byte of Hex FE (ID Address Mark) 1 Byte (Track Number) 1 Byte (Side Number) 1 Byte (Sector Number) 1 Byte (Sector Length, 02 for 512 Byte Sectors) 2 Bytes CRC (Cyclic Redundancy Check) 22 Bytes of Hex 22 12 Bytes of Hex 00 3 Bytes of Hex A1 (Data Hex A1, Clock Hex 0A) 1 Byte of Hex FB (Data Address Mark) 512 Bytes of Data 2 Bytes of CRC (Cyclic Redundancy Check) 38 Bytes of Hex 4E
GENERAL SPECIFICATIONS (CONTINUED)
4. FORMAT ORGANIZATION
PHYSICAL: Cylinders 0 thru 79 Sectors 1 thru 10 on Side 1 Sectors 1 thru 10 on Side 2 Sector Size 512 Bytes
LOGICAL: Tracks 1 thru 80 Sectors 0 thru 39 (Using physical Sectors 1 ... 10 — Side 1 and 2) Sector Size 256 Bytes
STORAGE: Total Unformatted Capacity 1 Megabyte Total Formatted Capacity 808,960 Bytes Maximum Sequential File Size 802,640 Bytes Maximum Relative File Size 182,880 Bytes Records Per Diskette 65,535 Files Per Diskette 296* Cylinders Per Diskette 80 Logical Sectors Per Cylinder 40 Physical Sectors Per Cylinder 20 Logical Bytes Per Sector 256 Physical Bytes Per Sector 512 Free Blocks Per Disk 3160
*More with Sub-Disk Partitioning
The following is a comparison between the Commodore 1541, 1571, and 1581 drives:
Blocks Available: 1541 - 664, 1571 - 1328, 1581 - 3160
 Disk Image Format
Disks for the 1581 disk drive are represented by the D81 disk image format. These disk images are used to transmit entire disks for use with emulators and mass storage devices.