POWER1

The POWER1 is a multi-chip CPU developed and fabricated by IBM that implemented the POWER instruction set architecture (ISA).

It was originally known as the RISC System/6000 CPU or, when in an abbreviated form, the RS/6000 CPU, before introduction of successors required the original name to be replaced with one that used the same naming scheme (POWERn) as its successors in order to differentiate it from the newer designs.

The POWER1 was introduced in 1990, with the introduction of the IBM RS/6000 POWERserver servers and POWERstation workstations, which featured the POWER1 clocked at 20, 25 or 30 MHz.

These upgraded versions were clocked higher than the original POWER1, made possible by improved semiconductor processes.

An indirect derivative of the POWER1 is the PowerPC 601, a feature-reduced variant of the RSC intended for consumer applications.

The open source GCC compiler removed support for POWER1 (RIOS) and POWER2 (RIOS2) in the 4.5 release.

Due to its modular design, IBM was able to create two configurations by simply varying the number of DCUs, RIOS-1 and a RIOS.9.

The chips are mounted on the “CPU planar”, a printed circuit board (PCB), using through-hole technology.

Due to the large number of chips with wide buses, the PCB has eight planes for routing wires, four for power and ground and four for signals.

The ICU contains the instruction cache, referred to as the "I-cache" by IBM and the branch processing unit (BPU).

In most processors, a multiply and an add, which is common in technical and scientific floating-point code, cannot be executed in one cycle, as in the POWER1.

All communications between the ICU, FXU and DCU chips as well as the memory and I/O devices is arbitrated by the SCU.

Although the DCUs provide the means to perform memory scrubbing, it is the SCU that controls the process.

The POWER1's I/O interfaces are implemented by the I/O unit, which contains an I/O channel controller (IOCC) and two serial link adapters (SLAs).

The two SLAs each implement a serial fibre optic link, which are intended to connect RS/6000 systems together.