README

FastDir

FastDir is a high-performance, drop-in replacement for the standard DIR command in MS-DOS and PC-DOS.

It is tailored specifically for vintage and low-spec systems (8088/8086, 286, 386) connected to modern, large storage solutions such as CompactFlash cards, SD adapters, and XT-IDE controllers. Native DOS utilities often crawl or freeze on large FAT volumes; FastDir eliminates these bottlenecks through low-level hardware optimizations, intelligent free-space detection, native localization, and memory-conscious algorithms.

Key Features

• Large Partition & FAT32 Support:
  • Probes for extended FAT32 free-space calls (Int 21h, AX=7303h) on any DOS 5.0+ kernel using defensive preset-carry detection, ensuring compatibility with DOSBox-X, FreeDOS, and Win9x while preventing crashes on older kernels.
  • Tracks directory sizes and drive totals using 64-bit accumulators (Comp in Turbo Pascal, Int64 in Free Pascal) to handle file trees and partitions far exceeding 2 GB.
  • Automatically detects Windows NT/2000/XP NTVDM free-space reporting caps.
• Long Filename Support (/LFN):
  • Experimental LFN integration via the DOS LFN API (Int 21h, AX=714Eh/714Fh/71A1h), working seamlessly under Windows 9x DOS, DOSLFN TSR, and NT-family NTVDM.
  • Implements a 64 KB per-directory bump-allocated string pool (TLfnPool) for long names, eliminating per-entry heap fragmentation.
  • Automatically formats into an adaptive 3-column layout under /W (with truncation glyphs) and displays long names along the right column in detail mode.
  • Gracefully and silently falls back to standard 8.3 filenames if no LFN provider is active.
• Flexible Display Modes & Internationalization:
  • Two-Column Detail Format (/2): DR-DOS style dual-column detailed view divided by a clean CP437 box-drawing vertical bar.
  • Human-Readable Sizes (/H): Formats byte counts into dynamically scaled units (bytes, KB, MB, GB) with one decimal precision under 10 units (e.g., 1.4 MB).
  • Native DOS Localization (InitCountry): Queries Int 21h, AH=38h on startup to honor the active COUNTRY= configuration, adapting thousands separators, decimal characters, date separators, date ordering (MDY, DMY, YMD), and time preferences.
  • Clock Toggling (/T): Inverts the default 12-hour or 24-hour clock determined by the country configuration.
• Extreme Output Performance:
  • 4 KB Buffered Console Output: Replaces the standard 128-byte DOS teletype buffer with a 4 KB buffer via SetTextBuf, drastically reducing Int 21h system calls during screen writes and redirects.
  • Zero-Allocation Streaming Mode: When sorting (/O) is omitted, file entries stream immediately as the filesystem returns them, bypassing heap overhead and lifting the 2,048-entry limit.
  • One-Pass Recursive Scan (/S): With broad match patterns (*.*), subdirectories are tracked during the primary enumeration pass, eliminating a redundant disk read per tree level.
• Instant Free Space Assessment:
  • Sampled FAT Mode (/QA): On FAT16 partitions under DOS 3.31+ (Compaq DOS 3.31 and DOS 4.0+), directly reads the boot sector and samples 8 evenly distributed FAT sectors via Int 25h to extrapolate available space in milliseconds.
  • Bypass Switch (/Q or /-F): Omits the free-space query entirely for instantaneous returns on sluggish media.
• Direct-to-Video Color Rendering (/C):
  • Renders colored text directly to video RAM (yellow for directories, light green for .COM, .EXE, and .BAT executables).
  • Requires no external drivers (no ANSI.SYS) and does not link the Borland Crt unit (eliminating Runtime Error 200 on fast CPUs).
  • Employs 4-line jump-scrolling via direct memory block copy to eliminate line-by-line scrolling stutter on slow 8088/8086 video subsystems.
  • Automatically falls back to standard output when piped or redirected to disk.
• Robust Memory Management & Safe Sorting:
  • Heap-allocated Quicksort avoids Real Mode 64 KB data segment (DSEG) limits.
  • Unsigned 32-bit timestamp comparisons (CmpUnsigned) correctly sort file timestamps with years $\ge 2044$ (bit 31 set) rather than incorrectly ordering them before 1980.
  • Precomputes extensions for /O:E sorting to prevent $O(n \log n)$ string extraction loops.

Command-Line Syntax

FASTDIR [drive:][path][filename] [/W] [/2] [/P] [/B] [/L] [/S] [/C] [/LFN] [/H] [/T] [/Q] [/QA] [/O:ord] [/A:att]

Options & Switches

Sorting (/O:order)

Specify one or more sort keys. Prefix keys with - to sort in descending order (e.g., /O:-S).

Attribute Filtering (/A:attrib)

Filter entries by their file attributes. Prefix attributes with - to exclude them (e.g., /A:-H-S). A bare /A displays all files, including hidden and system entries.

Environment Integration

FastDir parses the standard MS-DOS DIRCMD environment variable on execution. Switches can be concatenated without delimiters:

SET DIRCMD=/C/QA/O:GNE/H

You can alias or rename FASTDIR.EXE to DIR.EXE or run it from any directory in your PATH.

Compilation

Borland Turbo Pascal 6.0 / 7.0 (Target: 16-Bit Real Mode DOS)

tpc /M /B FASTDIR.PAS

Creates an optimized 16-bit real-mode binary compatible with DOS 3.30 and later.

Free Pascal Compiler (Target: 32-Bit DPMI / go32v2)

fpc -Tgo32v2 -O3 FASTDIR.PAS

Creates a 32-bit protected-mode DOS executable. Note: Direct Int 25h sector sampling (/QA) is disabled under DPMI and will automatically fall back to standard free-space detection routines.

Technical Specifications

• Target Architecture: IBM PC/XT/AT compatibles, 8088 through Pentium class.
• Minimum OS: MS-DOS / PC-DOS 3.30+ (DOS 3.31+ for /QA packet reads; DOS 5.0+ probed for extended FAT32 calls).
• Sort Limits: Up to 2,048 entries per directory when sorting (/O) is active. Streaming mode (sorting disabled) handles an arbitrary number of entries.
• Directory Nesting: Up to 256 subdirectories tracked per folder level during recursive search.
• LFN Memory Pool: Single 64 KB bump-allocated heap block per directory pass; display capped at 63 characters in sorted modes.