The 8048 has a Modified Harvard architecture, with internal or external program ROM and 64–256 bytes of internal (on-chip) RAM. The I/O is mapped into its own address space, separate from programs and data. Though the 8048 was eventually replaced by the very popular Intel 8051/8031, even at the turn of the millennium it remains quite popular, due to its low cost, wide availability, memory efficient one-byte instruction set, and mature development tools. Because of this it is much used in high-volume consumer electronics devices such as TV सेट्स। The 8049 has 2 KiB of masked ROM (the 8748 and 8749 had EPROM) that can be replaced with a 4 KiB external ROM, as well as 128 bytes of RAM and 27 I/O ports. The µC's oscillator block divides the incoming clock into 15 internal phases, thus with its 11 MHz max. crystal one gets 0.73 MIPS (of one-clock instructions). Some instructions are single byte/cycle ones, but a large amount of opcodes need two cycles and/or two bytes, so the raw performance would be closer to 0.5 MIPS. Reportedly, most if not all IBM PC AT and PS/2 keyboards contain a variant of the 8049AH microcontroller. An 8042 is located in the PC, and can be accessed through port 0x60 and 0x64 (personal computers using Pentium II or later microprocessors have the 8042 integrated into the Super I/O). Also 8042 controls A20 line and "soft boot" to switch Intel 80286 from protected to real mode.