CSS Optional — Paper-II, Section-A · Chapter 7
The textbook lists "Processor Types" as a topic distinct from CPU Architecture. Here the focus is on classifying processors by purpose, word size, and design philosophy, not on internal register structure (see CPU Architecture for that).
🗺️ Architecture Diagram — Processor Classification
graph TD
P["Processors"] --> GPP["General Purpose<br>Core i7, Ryzen"]
P --> MCU["Microcontroller<br>ATmega328, Cortex-M"]
P --> DSP["DSP<br>MAC unit, Harvard"]
P --> GPU["GPU<br>SIMD, 1000s of cores"]
P --> ASIC["ASIC<br>fixed function"]
P --> FPGA["FPGA<br>reconfigurable logic"]
1. Classification by Purpose
- General-Purpose Processor (GPP) — the CPU in a desktop, laptop, or server. Designed to run any program reasonably well rather than one program excellently. Examples: Intel Core i7, AMD Ryzen, Apple M-series.
- Microcontroller (MCU) — an entire small computer on one chip: CPU core + RAM + ROM/Flash + I/O ports + timers. Used in washing machines, cars, IoT devices. Examples: Arduino's ATmega328, ARM Cortex-M.
- Digital Signal Processor (DSP) — optimized for repetitive maths on continuous data streams (audio, video, radar). Its defining feature is a hardware MAC (Multiply-Accumulate) unit that performs
a = a + (b × c) in a single cycle, plus Harvard architecture for parallel instruction/data fetch.
- Graphics Processing Unit (GPU) — thousands of simple cores executing the same instruction across huge data sets. Classified as SIMD in Flynn's taxonomy. Now the workhorse of AI/ML training.
- ASIC (Application-Specific Integrated Circuit) — hardwired for exactly one task (e.g., a Bitcoin mining chip). Fastest and most power-efficient, but cannot be reprogrammed.
- FPGA (Field-Programmable Gate Array) — hardware whose logic gates can be rewired after manufacture. Sits between GPP flexibility and ASIC speed.
Comparison Table (high-yield)
| Processor |
Flexibility |
Speed for its task |
Power efficiency |
Typical use |
| GPP |
Highest |
Moderate |
Low |
PCs, servers |
| GPU |
Moderate |
Very high (parallel) |
Moderate |
Graphics, AI |
| DSP |
Moderate |
High (signal maths) |
Good |
Audio, telecom |
| Microcontroller |
Moderate |
Low |
Excellent |
Embedded devices |
| FPGA |
Reconfigurable |
High |
Good |
Prototyping |
| ASIC |
None (fixed) |
Highest |
Highest |
Crypto mining |
2. Classification by Word Size
The word size is the number of bits the CPU processes in one operation and typically the width of its registers.
- 8-bit / 16-bit — legacy and embedded systems.
- 32-bit — can address 2³² bytes = 4 GB of RAM. This is the hard reason 32-bit Windows could never use more than ~4 GB.
- 64-bit — can theoretically address 2⁶⁴ bytes = 16 exabytes. All modern desktop CPUs are 64-bit.
3. Classification by Design Philosophy
Briefly: RISC (simple fixed-length instructions, hardwired control, many registers) versus CISC (complex variable-length instructions, microprogrammed control). This comparison is examined so often it has its own page — see CISC vs RISC.