Memory Layout

On a 8080, there are no segments, the addresses are as displayed.

On on the 8086, a single segment with a value of 0x0100 is assumed. This implies that the first 4k of memory are not used.

The BDOS may be recompiled for starting at a lower address, in this case, the minimum memory requirement may be less than 64k.

Start	Size	Function
0xF000	4k	BDOS and hw drivers
	var	BDOS data
SP	var	Stack, growing down
		Free memory
0x0100	up to stack	Transient Program Area
0x0080	128 bytes	Command line and disk buffer
0x0000	128 bytes	System data area

Application program interface

It is using the call 5 convention with CP/M compatible syscall numbers.

File I/O is done via FCB blocks.