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Category Archives: BIOS
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
20 Comments
Detecting floppy drive presence and type
Detecting floppy drives is surprisingly tricky and poorly understood. The difficulty lies mainly in the interface between the floppy disk controller (FDC) and the actual drive(s). The interface isn’t particularly complex, but it isn’t straightforward, and it does not follow … Continue reading
Posted in BIOS, PC architecture
1 Comment
Interrupt 68h and EMM386
While working with a modified BIOS image in a virtual machine, I ran into mysterious hangs when trying to load an old version of EMM386.SYS from MS-DOS 4.01. A newer version of EMM386 did not exhibit the problem. A quick … Continue reading
Posted in BIOS, DOS, Virtualization
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The Fixed Disk Parameter Table
The Fixed Disk Parameter Table, or FDPT, is a structure primarily used by the BIOS in IBM compatible computers, but is also of critical importance to some (especially older) operating systems which do not use the BIOS. The FDPT was … Continue reading
Posted in BIOS, PC architecture, Virtualization
3 Comments
Geometry Problems
When introducing hard disk support in the PC/XT back in early 1983, IBM made a very unfortunate design decision: the information about drive geometry was exposed in the BIOS, and even worse, in the boot sector stored on the disk. SCSI … Continue reading
Posted in BIOS, PC architecture, Virtualization
2 Comments