01Overview
In 1964 the IBM System/360 unified a product line behind one compatible complex instruction set (CISC), so software could run across models. CISC tried to make each instruction do more in order to reduce memory accesses — a sensible trade when memory was expensive.
In the 1980s Patterson and Hennessy proposed RISC: simple, fixed-length, pipeline-friendly instructions, with the complexity pushed onto the compiler. MIPS and SPARC demonstrated the performance advantage. But x86 absorbed RISC ideas through microcode and superscalar execution, and ARM took mobile with low power. In 2010 RISC-V appeared as an open instruction set and opened a new phase of the argument.
02History
- 1964
IBM System/360
The model for CISC and for compatibility.
- 1980
RISC is proposed
Patterson starts the RISC project at Berkeley.
- 1985
MIPS R2000
A commercial RISC processor.
- 1990
ARM is founded
Low-power RISC moves into mobile devices.
- 2010
RISC-V
An open, extensible instruction set.
03Core concepts
Instruction set architecture
The contract between software and hardware: instructions, registers, memory model.
Pipelining
Fixed-length RISC instructions make fetch and decode easier to overlap.
Energy efficiency
Performance per watt, which matters more than peak speed in the mobile era.
04Hands-on
Do it once — it beats reading it ten times
Hand-assemble the same loop for a 2-address and a 3-address machine, then count instruction bytes fetched
05Self-check
Say it in your own words first, then open the answer. Whatever you cannot explain is what to review next.
Can you explain "Instruction set architecture"?
The contract between software and hardware: instructions, registers, memory model.
Can you explain "Pipelining"?
Fixed-length RISC instructions make fetch and decode easier to overlap.
Can you explain "Energy efficiency"?
Performance per watt, which matters more than peak speed in the mobile era.
What problem did it solve, and why was there nothing better at the time?
Go back to the history section: how was this done before, and what did it cost?
If you had to build it today, how would you break it down?
Use the hands-on task above: write a plan of at most three steps before you start.
06Key people
David Patterson
1947 –
A driving force behind RISC and RAID.
John Hennessy
1952 –
RISC and computer-architecture education.
07Further reading
- Computer Architecture: A Quantitative Approach
- The RISC-V Reader