The 1571 was released to match the Commodore 128, both design-wise and feature-wise. It was announced in the summer of 1985, at the same time as the C128, and became available in quantity later that year. The later C128D had a 1571-compatible drive integrated in the system unit. A double-sided disk on the 1571 would have a capacity of 340 KB (70 tracks, 1,360 disk blocks of 256 bytes each); as 8 KB are reserved for system use (directory and block availability information) and, under CBM DOS, 2 bytes of each block serve as pointers to the next logical block, 254 x 1,328 = 337,312 B or about 329.4 KB were available for user data. (However, with a program organizing disk storage on its own, all space could be used, e.g. for data disks.)
Depending on format, CP/M disks would format to 360 KB, with a mechanical maximum capacity of a 400 KB format (as with DD 5.25" drives generally).
The 1571 featured a "burst mode" when used in conjunction with the C128 (although not when used with the Commodore 64 or VIC-20). This mode replaced the slow bit-banging serial routines of the 1541 with a true serial shift register implemented in hardware, thus dramatically increasing the drive speed. Although this originally had been planned when Commodore first switched from the parallel IEEE-488 interface to a custom serial interface, hardware bugs in the VIC-20's 6522 VIA shift register prevented it from working properly.
The 1571 was noticeably quieter than its predecessor and tended to run cooler as well, even though, like the 1541, it had an internal power supply (later Commodore drives, like the 1541-II and the 3½" 1581, came with external power supplies). The 1541-II/1581 power supply makes mention of a 1571-II, hinting that Commodore may have intended to release a version of the 1571 with an external power supply. However, no 1571-IIs are known to exist. The embedded OS in the 1571 was CBM DOS V3.0 1571, an improvement over the 1541's V2.6. Read more at wikipedia.org