How Sinclair ZX Spectrum+3 Shows Disk Directory Listings

The Sinclair ZX Spectrum+3 introduced built-in floppy disk support, fundamentally changing how users managed data compared to traditional cassette tapes. This article explains the specific command used to view files, the layout of the directory screen, and the technical details of the +3 DOS system that governed these listings. Understanding this process provides insight into the storage architecture of one of the most popular home computers of the 1980s.

The CAT Command

To view the contents of a floppy disk on the ZX Spectrum+3, the user must utilize the CAT command within the BASIC environment. This command is short for “catalogue” and serves as the primary method for interrogating the disk drive. When the computer is powered on with a disk inserted, users can simply type CAT and press Enter. The system also supports specifying the drive side, using CAT 1 for side A and CAT 2 for side B, allowing users to browse double-sided 3-inch floppy disks without physically removing them.

Display Layout and Information

Upon executing the command, the Spectrum+3 clears the current screen and presents a text-based directory listing against the standard blue border and black background. The listing is organized into columns that display critical metadata for every file stored on the disk. Each entry typically includes the filename, which can be up to eight characters long, followed by the file type. Common types displayed include CODE for machine code, DATA for basic data, and ASC for ASCII text files.

Below the filename and type, the directory shows the starting sector number and the length of the file. Unlike modern operating systems that display file size in bytes or kilobytes, the +3 DOS primarily references sector counts, reflecting the physical structure of the floppy disk media. At the bottom of the screen, the system reports the total number of free sectors remaining on the disk, giving the user immediate feedback on available storage capacity.

Technical Context of +3 DOS

The directory listing is generated by the built-in +3 DOS, which resides in the computer’s ROM. This integration was a significant upgrade over previous peripherals like the DISCiPLE or +D, which required separate loading routines. The +3 DOS formats disks into 40 tracks per side with 9 sectors per track. When the directory is drawn, the operating system reads the File Allocation Table from the disk’s boot sector to construct the visual list. If a disk is unformatted or from an incompatible system, the directory command will return an error message rather than a listing, indicating the need for formatting or a different disk.