we’ve discussed already.
「但最近，這些驚喜變得不大令人愉快了，短期內恐怕仍會持續如此。」
，这一点在WPS官方版本下载中也有详细论述
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When DOS 5.0 and later runs with DOS=UMB, there will be not one but two memory arenas (assuming that UMBs are actually available). The AllocOper function (58h) was significantly extended to support UMBs.