The PPS-4 was built on a
metal gate process, compared to the contemporary
Intel 4004 which was based on the more advanced
silicon gate PMOS logic process. This required high voltages; it ran on a -17 VDC power supply while running at only 256 kHz, whereas the 4004 ran at 750 kHz on a 15 VDC supply. The CPU, part number 10660, was packaged in a 42-pin
quad in-line package. The pins included a 12-pin
address bus, 8-pin
data bus and three 4-pin
input/output ports that could be combined in different ways. Power supply and clock signals took up the rest of its 42 pins. PPS-4's separate data and address buses meant it could read an 8-bit instruction in a single cycle. In contrast, the 16-pin 4004 had a single 4-bit bus multiplexed five ways, meaning specifying a 12-bit address required external
latches and three cycles to specify the address and then two cycles to read an instruction. This meant the PPS-4 performed at roughly the same overall speed as the 4004 despite running at a third the clock speed. A complete system used the 10660 CPU, the 10706 clock generator in a 10-pin
TO-5 package, and one of a variety of ROM or RAM chips. The clock was four-phase and based on a standard
NTSC crystal due to their widespread availability. The PPS-4/2 was introduced in the autumn of 1975, combining the clock chip onto the die and reducing the system to two chips, the 11660 CPU and a ROM or RAM. It also had a built-in
LED controller. This would normally be used with the Memory/IO System chip, which combined 2 KB of ROM, 128 bytes of RAM, and 16 serial ports that could be combined in various ways. The PPS-4/1 followed in early 1976, staying with the PMOS process while most other companies had since moved to the new
NMOS logic. This was designed to work with the recently released PPS-8, which also used the PMOS process. The two were designed to work with a common set of interface chips. A wide variety of PPS-4/1 models were produced, with different amounts of RAM, ROM and I/O ports build into the die. These versions ran much slower than the original models, between 40 and 120 kHz. ==Notes==