TOS - Timex Operating System

TOS is the main OS when FDD/FDD3000 is used with a TC/ZX computer.

All disks formatted on TOS v2.0 are capable to boot FDD/FDD3000.

Currently, available TOS versions are:

TOS v2.0 – Timex Operating System:

The most popular system written by Timex. It emulates (we can say so…) ZX Microdrive. It is BASIC work ground. TOS treats RS232 as two files: CH_A.SCP is RS232 channel A and CH_B.SCP is RS232 channel B.

TOS root looks like a big disk with a maximum of four directories (drives). In the TOS root a CAT *”:” lists the SCP files and the available disks. All basic commands are available adding a *:

ATTR *, CAT *, CLOSE #*, MOVE *, DIM *, ERASE *, FORMAT *, GO SUB *, GO TO *, INPUT *#, LIST *, LIST *#, LOAD *, MERGE *, LET *, OPEN #*, PRINT *#, DRAW * and SAVE *.

For more detailed info about TOS commands please read the FDD user manual.

There are some undocumented commands and options in TOS: 

  • NEXT *;
    • Syntax: NEXT * pathname;
    • Works like the PATH variable in MS-DOS, but it can only contain one path;
  • FORMAT * (disk);
    • Syntax: FORMAT * “d” TO “diskname”d;
    • FORMAT a disk in drive “d” with the name “diskname” in 640K format. Do not use this option with a 40 tracks disk drive, it may damage the heads! This command is for use when a 80 tracks, double-sided disk drive is attached to the controller.

TOS tech info:

  • FDD interface is done for TOS. FDD interface activating at RST 8 and deactivating at jp or call to #604. Also call, jp, rst 0 activate FDD interface;
  • The first three tracks are taken by system, 4 for catalog rest for data;
  • System is swapped. Each track has 4K. Tracks used: 40;
  • Cluster size is 1K for 40 tr. and 4K for 80 tr;
  • Only the first 16K of the FDD is used by TOS;

Disk capacities are:

  • 140K for SS DD 40 tr;
  • 640K for DS DD 80 tr;
  • If using DS 40tr drive, the other side is not accessed, and users making switches;
For more technical info about TOS v A.2, please read the TOS Secrets page.

TOS v4.0 – by Wise Man.

This is a remake of TOS v2.0, has a compatible user interface and commands, as TOS 2.0 plus some addons, like easy access to FDD ram, built-in FOX monitor, etc.

It loads from “Boot disk” to all of the FDD RAM. All the TOS commands are in the RAM, so there is no swapping. Also “start” file is in the RAM (file selector/loader) and a few utilities, which fill the rest of RAM (48K) and vary due to release (eg. Tape>disk copier, disk copier, etc.) Each track has 4K, and disks formatted under TOS v4.0 differ from TOS v2.0 disks (but TOS v2.0 disks are still accessible): they have no system, they use 42 tracks, they have a directory on track 0 and a capacity of about 164K.

Everything would be cool for upgrading TOS v2.0 to v4.0, but Wise Man didn’t have 80 track drive, so left them unsupported. So 80 track disks are unaccessible, and TOS v4.0 cannot format them. You can still use 80 track drive as 40 track single-sided drive…


  • 164K for SS DD 40 tr (or 80 tr, TOS v4.0 use it as 40 tr ).