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
Feature | RAM (Memory) | SSD (Storage) |
---|---|---|
Speed | Very fast | Slower |
Volatility | Temporary (volatile) | Permanent (persistent) |
Capacity | GBs (small) | 100s GB–TB (large) |
Use | Running programs | Storing 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
orVec
, Rust asks the OS for memory using system calls (likemalloc
) - 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
Concept | Stack | Heap | Where in hardware? |
---|---|---|---|
What is it? | Memory for function calls and locals | Memory for dynamic data (Vec , Box , etc.) | RAM |
Managed by | Compiler + CPU | OS + allocator (e.g., malloc ) | RAM |
Hardware-level? | Yes (stack pointer) | Yes (address in RAM) | ✅ |
On disk/SSD? | ❌ Never | ❌ Unless out of RAM (swap) | ❌ |