8.3. Mechanical Layout

8.3. Mechanical Layout The system is designed to have as few boards as possible, so all boards are very large, about 50 cm square. All boards use low power Schottky TTL logic. The CPU consists of two boards, the processor and the MEMPPU. The MEMPPU contains the interface to memory, including virtual memory logic, and the interface to the I/O bus. The T/16 can have up to 512 kW (1 MB) of semiconductor memory or 256 kW of core memory. Memory boards come in three sizes: 32 kW core, and 96 kW and 192 kW semiconductor memory. This means that there is no way of getting exactly 1 MB of semiconductor memory with fully populated boards. Core memory has word parity protection, whereas semiconductor memory has ECC protection, which can correct a single-bit error and detect a double-bit error. Processor cabinets are about 6 feet high and house four CPUs with semiconductor memory or four CPUs with core memory. The processors are located at the top of the cabinet, with the I/O controllers located in a second rack directly below. Below that are fans, and at the bottom of the cabinet there are batteries to maintain memory contents during power failures. Most configurations have a second cabinet with a tape drive. The disk drives are freestanding 14-inch units. There is also a system console, a DEC LA-36 printing terminal.