Like the 15, a nearly identical job queue is available to the user in zero page (except for job 0), providing for exceptional degrees of compatibility. However, starting in 1991, Creative Micro Designs (CMD) made the FD-2000 high density (1.6 MB) and FD-4000 extra-high density (3.2 MB) 3½" drives, both of which offered not only a 1581-emulation mode but also 1541- and 1571-compatibility modes. With a storage capacity of 800 kB, the 1581 is the highest-capacity serial-bus drive that was ever made by Commodore (the 1-MB SFD-1001 uses the parallel IEEE-488), and the only 3½" one. The number of permitted directory entries was also increased, to 296 entries. The 1581 provides a total of 3160 blocks free when formatted (a block being equal to 256 bytes). The 1581 supports the C128's burst mode for fast disk access, but not when connected to an older Commodore machine like the Commodore 64. PC-style subdirectories were rejected as being too difficult to work with in terms of block availability maps, then still much in vogue, and which for some time had been the traditional way of inquiring into block availability. The version of Commodore DOS built into the 1581 added support for partitions, which could also function as fixed-allocation subdirectories. Unlike the 1571, which is nearly 100% backward-compatible with the 1541, the 1581 is only compatible with previous Commodore drives at the DOS level and cannot utilize software that performs low-level disk access (as the vast majority of Commodore 64 games do). Inexplicably, the drive's ROM contains commands for parallel use, although no parallel interface was available. Like the 15, the 1581 has an onboard MOS Technology 6502 CPU with its own ROM and RAM, and uses a serial version of the IEEE-488 interface. MOS 6502 2 MHz, WD1770 or WD1772 Ĭommodore proprietary serial IEEE-488 burst mode 9000 bytes/s USD 399 (1987) USD 1,000 (2023 equivalent) ģ½" floppy disk DS DD using MFM
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