Motorola 88100
Motorola's first 88000 RISC microprocessor, announced in 1988.
The Motorola MC88100 is a microprocessor that implements the 88000 RISC instruction set architecture. Announced in 1988, it was the first implementation of the 88000 architecture. The MC88100 features separate pipelined integer, floating-point add, floating-point multiply, and load/store execution units, dispatching at most a single instruction per clock cycle.
- Transistors (mc88100)
- 165,000
- Transistors (mc88200)
- 750,000
- Fabrication process
- 1.5 μm CMOS
- Number of user-accessible registers
- 64
- Number of general-purpose registers
- 32 (31 writable)
- Number of instructions
- 51
- Maximum registers accessed per instructi
- 6 (4 read, 2 write)
Lore & Background
The MC88100 was designed with a partitioned scheme that used separate MC88200 integrated circuits to optionally provide level 1 cache and a paged memory management unit. A typical system employed two MC88200s—one for instructions and one for data—and additional MC88200s could be added to increase cache size. This approach was chosen to allow system flexibility, letting the amount of cache vary depending on the price point. In practice, the additional chips required more circuit board space, and the buses between the MC88200s and the MC88100 added complexity and cost.
The MC88100 contained 165,000 transistors, while the MC88200 contained 750,000 transistors. Both were fabricated by Motorola in its 1.5 μm complementary metal–oxide–semiconductor process. The MC88100 was succeeded by the MC88110 in the early 1990s.
The MC88100 was ultimately commercially unsuccessful. This was due to a number of reasons, including the requirement of MC88200s in most cases, but was mostly due to Motorola being a vendor of the highly successful 68000 family. As the 68000 division viewed the 88000 as a competitor, they forced the MC88100 to be priced unacceptably high for a volume part. The part did find use in the high-end embedded market, in Motorola's own computers, and in large computers from companies such as Data General and the Unisys S-8400 Unix Servers.
Reader's Guide
The MC88100's significance lies in its role as Motorola's first implementation of the 88000 RISC architecture, a design that was technically advanced for its time with separate pipelined execution units and a flexible cache scheme using external MC88200 chips. However, its commercial failure illustrates how internal corporate dynamics can undermine a product: the 68000 division, viewing the 88000 as a competitor, priced the MC88100 unacceptably high for a volume part. This, combined with the requirement for additional MC88200 chips in most systems—which added board space, complexity, and cost—limited its adoption. Despite this, the MC88100 found niches in high-end embedded systems, Motorola's own computers, and large servers from Data General and Unisys. Its programming model, with 32 general-purpose registers (31 writable) and 51 instructions capable of accessing any register, is remarkably similar to DLX and, by extension, RISC-V based CPUs. The MC88100's legacy is thus twofold: as a technically interesting but commercially constrained RISC design, and as a cautionary example of how internal competition can hinder a company's own innovation.
Did You Know?
- The MC88100 contains 165,000 transistors, while the MC88200 contains 750,000 transistors.
- The MC88100's programming model is remarkably similar to DLX and RISC-V based CPUs.
Frequently Asked Questions
What is the Motorola MC88100?
It is Motorola's first RISC microprocessor, announced in 1988, and it serves as the original hardware realization of the 88000 instruction set architecture. The chip was built using a 1.5-micron CMOS process and contains roughly 165,000 transistors.
How does the MC88100 handle instruction execution?
The processor breaks work across four dedicated pipelined units—one for integer ops, one for floating-point addition, one for floating-point multiplication, and one for load/store. Despite having multiple execution paths, it can dispatch no more than a single instruction into the pipeline per clock cycle.
What does the MC88100's register file look like?
The architecture exposes 64 user-accessible registers to the programmer, of which 32 are general-purpose (with 31 actually writable). The entire instruction set is compact, comprising just 51 distinct opcodes.
Why do fans and historians consider the MC88100 important?
It was the very first silicon to prove out the 88000 RISC design, turning a paper architecture into a working chip back in 1988. Without it, the 88000 family—including the later, much larger MC88200 with 750,000 transistors—would never have existed.
How does the MC88100 compare to its successor, the MC88200?
The 88100 shipped with 165,000 transistors, while the follow-on MC88200 scaled up to 750,000 transistors, roughly a 4.5× increase. Both share the same 88000 instruction set, so the 88100 essentially set the architectural baseline that the 88200 expanded upon.
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