FLP_DENSITY density (density = S, D, H or E)


Location Gold Cards, SMS, SMSQ/E for QPC

There are four types of floppy disk drives which can be connected to a QL with a Gold Card (or to other computers which are running a QL emulator). The command FLP_DENSITY sets the type for use with FORMAT:

Sides Density Abbrev Capacity FLP_Density
Single Double SSDD 360 Kb S
Double Double DSDD 720 Kb D (Not QPC)
Double High DSHD 1440 Kb H
Double Extra DSED 3240 Kb E (Not QPC)

Parameters other than the four letters S, D, H and E, (including several characters or several parameters) are not allowed.




Tests have shown that it is not always advisable to FORMAT a disk to a lower density than would otherwise be possible, for example a high density disk to double density. The result may be that the number of good sectors is less than could have been achieved by formatting a disk of the lower density.

During testing, an undamaged double density disk was formatted to 1440 sectors and a high density disk to 2880 sectors, but if the high density disk had been formatted to double density, eg. with:


less than 1440 sectors might be good sectors.

You may also find that some disk drives which support the higher density will be unable to read these disks, since it will presume that they are FORMATted to their maximum density.


Since FLP_DENSITY only has any affect during formatting, it should generally be avoided. This does not really matter because a disk is automatically formatted to the highest possible density and it would be a waste of money to use a HD disk as a DD disk.


If a high or extra density disk is formatted on a system which does not support those capacities, it will be formatted to double density without any disadvantages. Such a disk does not cause problems when used with a Gold Card QL.


A double density disk cannot be formatted to a higher density with HD drives - the Level-2 (or Level-3) device driver will automatically reduce a density which had been set at too high a figure by FLP_DENSITY, to the appropriate figure. An ED drive however can successfully format HD disks and even DD disks to high and extra density, but such disks may be unreliable, ie. data could be easily lost.


High density is only supported on 3.5” disks, not 5.25” disks (widely used on MS/DOS systems). Extra density also only exists on 3.5” disks. QL DD and HD formatted disks have the same physical (but not software) format as MS/DOS and Atari TOS disks.


High density and Extra density disks are much faster than double density disks, ED disks can even be as fast as slow hard disks.


FLP_DENSITY overrides the in-built trial-and-error density detection which is slow for HD drives and even slower with ED drives. This can however cause problems when FORMATting DSDD disks - see FORMAT!


On SQMS/E for QPC, the same code letters may be added (after a *) to the end of the medium name to force a particular density format. (For compatibility with older drivers, if the code letter is omitted after the *, single sided format is assumed).

  • FORMAT ‘FLP1_Disk23’ Format at highest density or as specified by FLP_DENSITY.
  • FORMAT ‘FLP1_Disk24*’ Format single sided
  • FORMAT ‘FLP1_Disk25*S’ Format single sided
  • FORMAT ‘FLP1_Disk25*D’ Format double sided, double density

Also, FLP_DENSITY on it’s own resets automatic density selection.


The same effect as FLP_DENSITY can be achieved with a special FORMAT syntax. FLP_TRACK allows you to specify the number of tracks to be formatted onto a disk. STAT prints the name, good and free sectors of a medium. See also the The DMEDIUM_XXX functions, starting at DMEDIUM_DENSITY.