CPU Flashcards
(16 cards)
Arithmetic logic unit (ALU)
performs arithmetic, logical, and bitwise
operations on integer binary numbers.
Control unit (CU)
orchestrates the fetching (from memory), decoding and
execution (of instructions) by directing the coordinated operations of the
ALU, registers, and other components.
CPU
principal part of any digital computer system, generally composed of the main memory,
control unit, and arithmetic-logic unit and processes program instructions for output via
the instruction cycle.
Registers
small, fast storage locations inside the CPU used to hold data, addresses, or instructions that the CPU is actively working with.
They are the fastest memory in a computer, even faster than cache or RAM, but very limited in size (usually just a few dozen total).
There are different types of registers, each with a specific job, such as:
Holding data to be processed
Keeping the address of the next instruction
Storing the results of operations
Managing program execution
Accumulator
most frequently used register used to store data taken from memory.
Memory Address Register (MAR)
The MAR holds the location (or address) in memory where the CPU wants to look for data or store data.
You can think of it like writing down the street address of a house the CPU wants to visit.
It’s the “where” part of memory access.
🏠 “I want to go to memory address 105 to grab some data” → the CPU writes 105 in the MAR.
Memory Data Register (MDR)
The MDR holds the actual data being moved to or from memory.
If the CPU is reading, MDR temporarily stores the data coming in.
If the CPU is writing, MDR holds the data going out.
📦 Think of MDR as the box used to carry stuff to or from a memory shelf. The MAR gives the shelf number, the MDR carries the item.
Program Counter (PC)
The PC keeps track of where the CPU is in the program.
It stores the address of the next instruction the CPU should run.
After each instruction is finished, the PC moves to the next one.
📍 Think of the PC as a bookmark in your code — it always points to the next line to read.
Instruction Register (IR)
The IR holds the actual instruction the CPU is about to carry out.
When the CPU reads an instruction from memory (using the PC), it stores that instruction in the IR.
The CPU then executes the instruction from the IR, while the PC moves ahead to the next one.
🛠️ If the PC is your bookmark, the IR is the page you’re reading right now.
Pipelining
a technique that allows a CPU to work on multiple instructions at the same time, by breaking the work into stages and overlapping them.
Instead of completing one instruction per clock cycle, pipelining lets the CPU start a new instruction every cycle, while other instructions are already in progress.
32 vs 64 Architecture
32 compatibles with 32 or 64. 64 only compatible for 64
○ 32 process up to 4GB RAM. 64 process up to 16 Exabytes of RAM
64- or 32-bit data path
refers to the number of bits transferred per clock cycle (more is
faster)
CISC (Complex Instruction Set Computing)
CISC is a type of CPU design where the processor has a large number of complex instructions — some instructions can do multiple things at once (like load, calculate, and store in a single command).
🔑 Key Features of CISC:
Many instructions, often hundreds
Some instructions take multiple clock cycles
Designed to minimize the number of instructions needed to write a program
More hardware complexity, less software complexity
x86
x86 is a family of CISC processors developed by Intel (and AMD).
It originally referred to Intel’s 8086 CPU series, but now x86 usually refers to:
32-bit and 64-bit CPUs based on that architecture
Operating systems and software that run on these processors
So, x86 = real-world CISC used in most desktop/laptop computers today.
RISC - Reduced Instruction Set Computer
RISC is a CPU design approach that uses a small, highly optimized set of simple instructions, each designed to execute very quickly — ideally in one clock cycle.
The goal of RISC is to simplify the hardware so that instructions are:
Fast to execute
Easy to decode
Easier to pipeline and optimize
ARM - Advanced RISC Machines
is a family of CPU architectures based on the RISC design philosophy.
It uses simple, power-efficient instructions (RISC = Reduced Instruction Set Computer)
Originally designed for low-power mobile devices
Now also used in desktops, laptops, servers, embedded systems, and IoT
ARM doesn’t manufacture chips — it licenses its architecture to companies like Apple, Qualcomm, Samsung, and NVIDIA, who design their own custom chips.
