The PC-9801 was a very popular PC in Japan. PC-9801's design was very similar to IBM-PC, but was slightly extended. VRAM (Video RAM) is strongly extended from original IBM-PC, enabling it to display kanji characters without bitmap memory (as ASCII characters). But I/O systems, Interrupt systems are almost the same.
There were in fact three models : F1, F2 and F3. Whereas F1 & F2 models have only 128k RAM, the F3 had 256 kb RAM and 10 Mb hard-disk built-in.