Data Size Units and Memory Units Cheat Sheet
- Bit (b): The smallest unit of digital information (0 or 1).
- Nibble: 4 bits.
- Byte (B): Commonly 8 bits.
| Unit | Abbreviation | Factor | Exact Bytes |
|---|
| Kilobyte | KB | 10³ | 1,000 bytes |
| Megabyte | MB | 10⁶ | 1,000,000 bytes |
| Gigabyte | GB | 10⁹ | 1,000,000,000 bytes |
| Terabyte | TB | 10¹² | 1,000,000,000,000 bytes |
| Petabyte | PB | 10¹⁵ | 1,000,000,000,000,000 bytes |
| Exabyte | EB | 10¹⁸ | 1,000,000,000,000,000,000 bytes |
| Unit | Abbreviation | Factor | Exact Bytes |
|---|
| Kibibyte | KiB | 2¹⁰ | 1,024 bytes |
| Mebibyte | MiB | 2²⁰ | 1,048,576 bytes |
| Gibibyte | GiB | 2³⁰ | 1,073,741,824 bytes |
| Tebibyte | TiB | 2⁴⁰ | 1,099,511,627,776 bytes |
| Pebibyte | PiB | 2⁵⁰ | 1,125,899,906,842,624 bytes |
| Exbibyte | EiB | 2⁶⁰ | 1,152,921,504,606,846,976 bytes |
| Term | Typical Size | What Is It? | Where Is It? | Who Uses It? | Why This Size? |
|---|
| Cache Line | ~64 bytes (on modern CPUs) | Smallest chunk of data fetched/stored by CPU cache | CPU caches (L1, L2, L3) | CPU hardware, cache controller | Balances transfer overhead vs. spatial locality; 64 bytes is common for modern architectures |
| Memory Page | 4 KB (commonly), 2 MB, 1 GB | Fundamental unit of virtual memory management | System RAM, managed by the OS | OS, CPU MMU (Memory Management Unit), TLB | Standard 4 KB minimizes overhead of page tables; larger pages (2 MB, 1 GB) reduce TLB pressure for big data workloads |
| Disk Block | Typically 512 bytes or 4 KB | Smallest addressable unit on storage devices (HDD, SSD) | Physical storage (disk/SSD) | Disk controllers, file systems | Historically 512 bytes was standard; many drives now use 4 KB for efficiency and error correction |
| File-System Block | Often 4 KB, can be bigger | Unit in which file systems allocate and manage disk space | File system layer on top of disk blocks | OS file system driver, user-level I/O | Matches or aligns with disk block size and common page size for simpler I/O and reduced fragmentation |