Monthly Archives: September 2011

WordStar needs address wraparound?

The CP/M compatible interface in DOS was initially documented, later forgotten, and then re-discovered every once in a while. In 1989, John Switzer described parts of the CALL 5 system call interface mechanism in a slightly hysterical article as a “back … Continue reading

Posted in DOS, PC architecture | 9 Comments

Who needs the address wraparound, anyway?

The infamous A20 gate is well known and documented in hair-raising detail. What’s much less well documented is the real purpose of the A20 gate, that is, who actually needs the 8086 address wrap-around to be emulated in the first … Continue reading

Posted in DOS, PC architecture | 1 Comment

IBM DOS 5.0 QBASIC hangs on non-IBM systems

Much like its predecessors, IBM DOS 5.0 has no trouble running on clone systems, as long as they’re sufficiently compatible. That includes virtual machines. However, the QBASIC.EXE (and consequently EDIT.COM) program dated May 9, 1991 consistently hangs on any non-IBM … Continue reading

Posted in BIOS, DOS, PC history | 19 Comments

Hang with early DOS boot sector

While installing various versions of DOS for the DOS history series of articles, I was faced with a mysterious problem: Some versions of DOS would hang right away when booting from fixed disk, but not from floppy. I already knew … Continue reading

Posted in DOS | 15 Comments