The 64 KB main memory is made of four rows of eight type 4116 dynamic RAM chips, each with 16,384 bits. Memory is shared, with 60 KB available for software and 4 KB reserved for video memory. No parity is provided and no provision for memory expansion exists on the motherboard. The boot program loader and significant parts of the BIOS are stored in a 4 kilobyte EPROM, which is bank-switched. A second EPROM is used as a fixed character generator, providing upper and lower case ASCII characters and graphic symbols; the character generator is not accessible to the CPU. The eighth bit of an ASCII character is used to select underlined characters. Serial communications is through a memory-mapped Motorola MC6850 Asynchronous Communications Interface Adapter (ACIA); a jumper on the motherboard allows the MC6850 to be set for either 300 and 1200 baud or 600 and 2400 baud communications, but other bit rates are not available.