SCSI INQUIRY Command Explained¶

The INQUIRY command provides essential identification information from a SCSI device, including Vendor, Product, and Device Type. The data in the sample table below originates from this command.

Vendor   Product          Device type
-------- ---------------- ------------------------------
NDMICROP 1375             Direct
TANDBERG TDC 3600         Sequential (streamer)
OSI      LD 1200 SCSI     Write Once (optical disk)
NDCDC    EMD 97201 (736)  Direct
NDCDC    EMD 97201 (368)  Direct
NDSTK    2925             Sequential (magtape)
ARCHIVE  VIPER 150 21247  Sequential (streamer)

INQUIRY (Opcode 0x12)¶

Purpose¶

The INQUIRY command allows a host (initiator) to retrieve identification data from a target device. Returned information includes:

Peripheral Device Type (e.g., Direct Access, Sequential Access)
Vendor Identification
Product Identification
Product Revision Level

Command Descriptor Block (CDB)¶

Byte	Bits	Description	Example
0	7:0	Operation Code	`0x12`
1	7	EVPD (Enable Vital Product Data)	`0` for standard inquiry
2	7:0	Page Code (ignored if EVPD=0)	`0x00`
3–4	15:0	Allocation Length (bytes to return)	`0x0024` (36 bytes typical)
5	7:0	Control	`0x00`

Example CDB (hex):

12 00 00 00 24 00

Standard INQUIRY Data Format¶

Offset	Length	Field	Description	Example
0	1	Peripheral Device Type	0x00 = Direct Access, 0x01 = Sequential Access, etc.	0x00
8	8	Vendor Identification	ASCII string	`NDMICROP`
16	16	Product Identification	ASCII string	`1375`
32	4	Product Revision Level	ASCII string	`1.00`

These fields correspond directly to the data presented in the summary table.

Device Type Values¶

Code	Meaning	Example
00h	Direct Access (Disk)	`NDMICROP 1375`
01h	Sequential Access (Tape/Streamer)	`TANDBERG TDC 3600`
04h	Write Once (Optical Disk)	`OSI LD 1200 SCSI`
05h	CD-ROM	–
07h	Optical Memory	–
08h	Medium Changer	–
1Fh	Unknown/No device	–

Example Command Usage (Linux)¶

Using the sg_inq utility from the sg3_utils package:

sg_inq /dev/sda

Output Example:

standard INQUIRY:
  PQual=0  Device_type=0  RMB=0  version=0x05  [SPC-3]
  [Vendor identification: NDMICROP]
  [Product identification: 1375]
  [Revision level: 1.00]

Which corresponds directly to:

Vendor   Product          Device type
-------- ---------------- ------------------------------
NDMICROP 1375             Direct

Summary Table¶

Information	Source	SCSI Command
Vendor ID	Standard INQUIRY bytes 8–15	INQUIRY (0x12)
Product ID	Standard INQUIRY bytes 16–31	INQUIRY (0x12)
Device Type	Peripheral Device Type bits 4–0 of byte 0	INQUIRY (0x12)

Optional Extension¶

Would you like to include an annotated hex dump example of an INQUIRY response showing byte-by-byte decoding (for use with bus traces or emulators)?