利用中断15H使用扩展内存

The Utilizaton of Extended Memory with Interrupt 15H

近年以INTEL80286为CPU的微机大量投入使用。该类机大都拥有24位地址总线,1兆以上的内存,如某些PC/AT、PS/250、AST286等。但由于仍旧采用DOS3.X操作系统,一般情况下用户能直接使用的仅为640K的主内存。对其余地址在1MB以上的扩展内存,DOS仅提供了一个VDISK.SYS的虚拟盘驱动程序,带E参数时,可把扩展内存作为磁盘使用。实际上,这批新型微机ROM BIOS的中断15H,提供了直接把扩展内存作为数据区使用的可能性。熟悉微机中断的人都知道,在IBM PC的家族中,早期的PC机,其中断15H为盒式磁带机的I/O控制。而得到广泛使用的PC/XT机没有盒带机的硬件接口。

This paper describes a method of using extended memory as data area in the microcomputer with a CPU of 80286. Under MS-DOS operate system, the direct use of extended memory by software couldn't be supported. Since the 80286 CPU has a greater address ability in the protected mode than in the actual mode, it is possible to force the CPU into the protected mode through the employ of interrupt 15H from the ROM BIOS, and after the data movement from or to the extended memory had been completed, it was returned to the actual mode used by MS-DOS. Finally, a assemble language program is given to show the use ofextended memory by this method.