clones for using Windows 95. The status of the PC-98 series is not based on its hardware feature or the number of softwares and peripherals, but its strength in promotion, parts procurement and faith in the NEC brand." In 1997, NEC introduced the PC98-NX series as a main personal computer line that conformed to the PC System Design Guide and were IBM PC compatible. The PC-9801's last successor was the Celeron-based PC-9821Ra43 (with a clock frequency of 433 MHz, using a 440FX chipset-based motherboard design from 1998), which appeared in 2000. NEC announced that the PC-98 would be discontinued in 2003. 18.3 million of PC-98s shipped by the end of shipments in March 2004. The last version of Windows to support PC-98 is Windows 2000. Hardware The PC-98 is different from the IBM PC in many ways; for instance, it uses its own 16-bit C-bus (Cバス) instead of the ISA bus; BIOS, I/O port addressing, memory management and graphics output are also different. However, localized MS-DOS, Unix, OS/2, or Windows will still run on PC-9801s. Expansion bus All PC-98 desktop models use a 100-pin expansion slot. It has 16 data lines and 24 address lines. The bus frequency is fixed at 5, 8 or 10 MHz. The PC-H98 and PC-9821A series computers use a proprietary 32-bit local bus slot along with 16-bit slots. The 16-bit expansion bus was also called C-bus (Compatible Bus). The PC-9821Xf introduced in 1994 shipped with C-bus slots and PCI slots on the motherboard, replacing the proprietary local bus slot. Memory Many PC-9801 models can increase system memory by installing expansion boards, daughterboards, or proprietary SIMMs. They are limited to 14.6 MB, due to 24-bit address pins and reserve space. EMS memory boards for C-bus are also available. The PC-9821Af introduced in 1993 shipped with standard 72-pin SIMMs, broke the 14.6 MB barrier, and supported memory up to 79.6 MB. Later desktop models shipped with standard SIMM or DIMM memory. The PC-98XA (1985) and its successors, called high-resolution machine or simply hi-reso machine, are capable of 768 KB base memory, but their I/O ports and memory addressing are quite different from normal PC-98s. Storage Early PC-9801 models supported 1232 KB 8-inch floppy drives and/or 640 KB -inch floppy drives. Each used different IRQ lines and I/O ports. Later models support both interfaces. High density -inch and -inch floppy disks use the same logical format and data