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File systems compared

How drives work · Where each file system is used, how it finds files, what safety features it has, and how good the chances of recovery are.

A file system is the filing scheme inside a partition: a table of contents (where each file's name, dates and pieces are) plus the space the contents live in.

File system	Where you see it	Limits	How files are found	Safety features	Recovery outlook	DiskSalvor
NTFS	Windows drives, most external HDDs	Very large files and volumes	Master File Table: one 1 KB record per file	Journal ($LogFile), mirror of the first 4 records, backup boot sector	Very good: records are self-contained; folders can be rebuilt	Full: list, copy, deleted files, deep search
FAT32	USB sticks, SDHC cards, EFI partitions	Files up to 4 GB; Windows formats it up to 32 GB	Folder entries + the FAT chain	Two copies of the FAT, backup boot sector at sector 6	Good for unfragmented files; deleted chains are erased	Full
FAT12/16	Old or tiny cards, floppies	Volumes up to 2–4 GB	Same as FAT32	Two FAT copies	Same as FAT32	Full
exFAT	SDXC cards, cameras, big USB sticks, drives shared with Macs	Huge files	Folder entry sets + bitmap; FAT only for fragmented files	Boot region checksum + full backup; no journal	Very good for unfragmented files	Full
ReFS	Windows Server, Storage Spaces	Very large	B+ trees, copy-on-write	Checksums on metadata	Needs specialist tools	Identifies it
ext4	Linux, many NAS boxes	Large	Inodes in block groups	Journal; superblock copies throughout the disk	Good with Linux tools	Identifies it, reads basic info
APFS / HFS+	Macs, Mac-formatted external drives	Large	B-trees	APFS: copy-on-write, snapshots	Needs Mac-aware tools	Identifies it
BitLocker, LUKS	Encrypted volumes (Windows, Linux)	–	Encrypted: unreadable without the key	–	Only with the key	Identifies and explains

Other things you may find on a disk: Linux swap (no files), LVM and Storage Spaces (containers that hold file systems), and ISO 9660 (CD/DVD images).

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DiskSalvor is free, open-source data recovery for failing drives on Windows. It never writes to the drive, gets the easy files off first, goes back for the rest round by round, and explains what it's doing in plain English. No file limits, no paid edition, no account.

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Start here if your drive is failing

Common situations: what to doDrive asks to be formatted, isn't detected, shows 0 bytes, clicks or is very slow: the most likely cause of each, and what to do first.
Windows pop-ups on a damaged drive: what to clickWhat Windows' format, scan-and-fix and initialize prompts mean on a damaged drive, and which button keeps your files safe.
When the file index is damagedWhy a drive turns RAW after a power cut or unplug, why your files are usually still there, and how they're recovered.
Bad sectors, retries and hangsWhat a bad sector is, why one bad spot can freeze Windows for minutes, and how to read a failing drive without making it worse.
The drive's health log (S.M.A.R.T.)What S.M.A.R.T. values like reallocated and pending sectors mean, why a failing drive can still say 'passed', and which numbers matter.
How the safe copy worksWhy copying a failing drive once, easy parts first, protects your files, and how an image lets you recover from the copy instead.
What can be fixed, and whenBoot sector, partition table, file index, bad sectors: what can be repaired, and why repairs should wait until your files are safe.
Deleted, quick-formatted, fully formatted, wipedWhat deleting, quick formatting, full formatting and wiping change on a hard drive, SSD or memory card, and the chances for each.

How drives work

The big picture: a drive is a stack of layersFrom numbered sectors to partitions, file systems and your files: the layers of any drive, and why 'format the disk' usually means one is damaged.
Kinds of drivesWhat's inside each kind of drive, how each usually fails, whether deleted files can come back, and whether it keeps a health log.
How a drive connects, and why it mattersWhy the same disk behaves differently in different USB enclosures, and what bridges and card readers mean for recovering data.
Inside: platters vs flashHow hard disks and flash drives store data, why disk order matters on a hard drive, and why deleted data on an SSD is usually gone.
Sectors, LBAs and clustersThe smallest units a drive and a file system work in: sectors, 512e and 4Kn, logical block addresses and clusters.
Partition tables: MBR and GPTWhat MBR and GPT partition tables hold, which one has a backup copy, and why a USB stick with no partition table is normal.
Inside NTFSHow NTFS finds your files through the Master File Table and folder listings, and why files can be recovered when parts of the MFT are lost.
Inside FAT32 and exFATHow FAT32 and exFAT store folders and file chains, what deleting changes, and which deleted files come back whole.
What Windows does when you plug in a driveDrivers, Disk Management, indexing and thumbnails: what Windows does to a drive on its own, and how to stop it straining a failing one.
What has a backup copy, and what doesn'tWhich disk structures have backups (GPT, the NTFS boot sector, the MFT mirror) and which don't, so you know what can be rebuilt.
EncryptionHow BitLocker and enclosure encryption affect recovery, where the keys are, and why some WD drives only read through their own USB bridge.

Reference

Where DiskSalvor fitsHow DiskSalvor reads a drive as raw sectors, layer by layer, without writing to it, even when Windows calls the volume RAW.
GlossaryPlain-English meanings of bridge, carving, CHKDSK, LBA, MFT, RAW, S.M.A.R.T., TRIM and other drive and recovery terms.