Quick Release Sector Transfer

File Format
Name	Quick Release Sector Transfer
Ontology	Electronic File Formats Disk Image Formats Quick Release Sector Transfer

The QRST disc image format was used by Compaq to distribute disk images of diagnostic software. The file QRST.EXE would be supplied with the disc images to write them to a floppy drive.

Identification

QRST files start with the 4-character ASCII string QRST, followed by a 0x00 byte. The first character of the file extension is an underscore, followed by a 2-digit hexadecimal volume number.

Structure

File header

The file begins with a 796-byte header:

Offset	Size	Description
0x00	5 bytes	Magic number, QRST followed by 0x00
0x08	4 bytes	Checksum
0x0C	1 byte	Disk capacity: Value Meaning 0 unknown 1 360k 2 1.2M 3 720k 4 1.4M 5 160k 6 180k 7 320k
0x0D	1 byte	Current volume number in set
0x0E	1 byte	Count of volumes in set
0x0F	96 bytes	Description, ASCIIZ
0x4B	721 bytes	Disk label, ASCIIZ

Tracks

The header will be followed by the data tracks. These can be in one of three forms:

Uncompressed track

Offset	Size	Description
0x00	1 byte	Cylinder
0x01	1 byte	Head
0x02	1 byte	0 indicates uncompressed track
0x03	calculated from disk type in header	Track data, uncompressed

Blank track

Offset	Size	Description
0x00	1 byte	Cylinder
0x01	1 byte	Head
0x02	1 byte	1 indicates blank track
0x03	1 byte	Filler byte

Compressed track

Offset	Size	Description
0x00	1 byte	Cylinder
0x01	1 byte	Head
0x02	1 byte	2 indicates compressed track
0x03	2 bytes	Length of compressed data
0x05	As specified above	Compressed data

The compressed data stream consists of alternating literal runs (a byte giving the length of the run, followed by that number of bytes data) and compressed runs (two bytes; first gives number of repeats, second gives byte to repeat).

Sample files

• Compaq Portable III setup and diagnostics