5203) printer was attached to the main system. The 5203 was a chain printer with interchangeable cartridges. It could run at 100 or 200 lines per minute, based on model. Later on, IBM offered multiple models of the existing IBM 1403 printer line, which had been originally built for the IBM 1401 computer. Floppy disk With the arrival of the IBM 3740 data entry system, the System/3 Model 10 got a feature called LCA (local communication adaptor) which allowed an IBM 3741 station to be "attached" to the system to transmit/receive data. Later models of the System/3 such as the Model 8 were cardless and used the 8" 3740 style floppy disk. Instruction set The instruction set was optimised for two key aspects of the product: limited availability of main memory, and the RPG II programming language. The original S/3 (models 10 and then 6, 8 and 12) had 29 instructions, all occupying between 3 and 6 bytes (24 to 48 bits). The first 4 bits conveyed a lot of information: "1111" meant this was an instruction without operands, known as a command. e.g. Start I/O (the I/O op being defined by previously loaded I/O registers). "11xx" and "xx11" meant a 1-operand instruction, such as a Branch. If xx was 00 the operand was addressed by its full 16-bit address. xx=01 or 10 meant base-displacement addressing was used, using index register 1 or 2 respectively. A base address would previously have been loaded into one of the two index registers and the instruction contained the displacement of up to just 256 bytes (8 bits of addressing). Other patterns for this first half-byte indicated a 2-operand instruction. "0000" meant both operands were addressed by their direct 16-bit address. "0100": operand 1 uses reg 1 as its base; operand 2 uses direct addressing. "0110": operand 1 uses reg 1 as its base, operand 2 uses reg 2. And so on. The remaining 4 bits of the first byte further defined the instruction. This structure meant that there was the capability to have up to 64 operations in all: 16 commands (though there were never more than five across the whole product range); 16 1-operand instructions starting with 11xx; 16 1-operand instructions starting with xx11; 16 2-operand instructions. As well as the two index registers already mentioned (referred to as 1 and 2, or binary 01 and 10) there were other registers. "Reg