Register, RAM, SSD, STACK, HEAP

1. Register

  • 🧬 What it is: The smallest and fastest memory inside a CPU.
  • 📏 Size: Typically 32, 64, or 128 bits.
  • ⚡ Speed: Blazing fast (nanoseconds).
  • 🔁 Use: Stores data the CPU is immediately operating on (e.g., numbers during calculations).

2. RAM (Random Access Memory)

  • 🧠 Also called memory.
  • 📏 Size: GBs (e.g., 8GB, 16GB).
  • ⚡ Speed: Fast, but slower than registers.
  • 🔁 Use: Stores data and programs that are currently being used.
  • ❌ Volatile: Data is lost when power is off.

3. SSD (Solid State Drive)

  • 📦 Also called storage or disk.
  • 📏 Size: 100s of GBs to TBs.
  • 🐢 Speed: Much slower than RAM and registers, but faster than HDDs.
  • ✅ Persistent: Keeps data even when powered off.
  • 🔁 Use: Stores files, programs, OS, databases, etc.

Memory vs. Storage

FeatureRAM (Memory)SSD (Storage)
SpeedVery fastSlower
VolatilityTemporary (volatile)Permanent (persistent)
CapacityGBs (small)100s GB–TB (large)
UseRunning programsStoring programs/files

What is an HDD?

HDD stands for Hard Disk Drive — it’s a mechanical storage device used to store data persistently (even when the power is off).

Stack and Heap

both stack and heap are part of RAM — real hardware memory.

When you run a program, the operating system loads it into RAM, and then divides that RAM into different regions:

sqlCopyEdit+-----------------------------+
| Program Code (read-only)   |
+-----------------------------+
| Static / Global Variables  |
+-----------------------------+
|       Stack (grows down)   |
|       (local vars, calls)  |
+-----------------------------+
|       Heap (grows up)      |
|    (Vec, Box, dynamic data)|
+-----------------------------+

So:

Stack and Heap are software-managed regions of RAM — not separate hardware.

Stack details

  • Managed by hardware (CPU maintains a stack pointer register)
  • When a function is called, it pushes its locals to the stack
  • When it returns, it pops them off
  • Super fast because it’s just arithmetic on the stack pointer

Limit: OS sets a fixed stack size — exceed it and you get a stack overflow.


📦 Heap details

  • Managed by the OS’s memory allocator
  • When you create a Box or Vec, Rust asks the OS for memory using system calls (like malloc)
  • Heap allocations are slower, but more flexible
  • Memory must be manually freed (Rust automates this via ownership)

🧠 What about SSD / Disk?

  • SSD and disk come in when:
    • You run out of RAM → OS swaps unused memory to disk (very slow)
    • You explicitly read/write files
  • But stack and heap always live in RAM, not SSD — unless you’re out of memory and the OS starts swapping.

🧾 Summary

ConceptStackHeapWhere in hardware?
What is it?Memory for function calls and localsMemory for dynamic data (Vec, Box, etc.)RAM
Managed byCompiler + CPUOS + allocator (e.g., malloc)RAM
Hardware-level?Yes (stack pointer)Yes (address in RAM)
On disk/SSD?❌ Never❌ Unless out of RAM (swap)

Leave a Reply

Your email address will not be published. Required fields are marked *