SD and ED enhanced density
A standard 1050 reads and writes 810-compatible SD and enhanced density, or ED. ED uses 26 sectors of 128 bytes per track instead of SD's 18. This gives a nominal 130 KiB before file system overhead.
The term dual density here refers to supporting two densities. It does not mean DD with 256-byte sectors, which requires a drive upgrade.
Disks and DOS 2.5
The drive has a separate power supply, two SIO sockets and drive-number switches. DOS 2.5 supports both standard formats. Exchanging files with an Atari 810 requires SD: the 810 cannot read ED disks regardless of the program stored on them.
Formatting erases a disk's previous contents. It acts on the disk in the selected drive, D1:, D2: and so on.
US Doubler and other upgrades
Modifications such as ICD's US Doubler add DD and faster transfers. A compatible DOS is required to use these features. An upgraded 1050 can therefore write formats unavailable on a standard unit.
US Doubler, Happy and Speedy differ in installation and operation. Identify the installed upgrade before repair or configuration; a switch on the case alone does not identify it.
Sources and further reading
- Atari 1050 Disk Drive Field Service Manual Rev. 03, October 1985 ↗
- ICD 1050 UltraSpeed Hardware Installation — original US Doubler guide ↗
- COMPUTE!, October 1985: Atari Disk Drive Compatibility — ED, DD and Percom ↗
- Atari DOS 2.5 / XF551 Owner’s Manual — SD/ED format support ↗
- Atari DOS XE / XF551 Owner’s Manual, appendix B — SD/ED geometry ↗