System Internals:SLIC DASD device recognition - Revision history

PoC: ±Cat/AI heading

2026-08-16T19:22:48Z

±Cat/AI heading

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	The '''SLIC DASD device recognition''' table is the static list, inside the OS/400 Licensed Internal Code (SLIC), of which SCSI disk drives the system will accept as a DASD (disk) unit. This page describes how that recognition works, how to find and decode the table in a SLIC image, and — as a worked example — the complete list a V4R4 machine accepts. The method generalises to any release and to other SLIC device tables.		The '''SLIC DASD device recognition''' table is the static list, inside the OS/400 Licensed Internal Code (SLIC), of which SCSI disk drives the system will accept as a DASD (disk) unit. This page describes how that recognition works, how to find and decode the table in a SLIC image, and — as a worked example — the complete list a V4R4 machine accepts. The method generalises to any release and to other SLIC device tables.

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PoC: +cat

2026-08-16T19:06:47Z

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Friedkiwi: Revert to pre-session Notes (holding wiki changes for this research per request) (via update-page on MediaWiki MCP Server)

2026-08-15T18:58:53Z

Revert to pre-session Notes (holding wiki changes for this research per request) (via update-page on MediaWiki MCP Server)

← Older revision		Revision as of 20:58, 15 August 2026
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	== Notes ==		== Notes ==

	* "Ide" in SLIC symbol names (~~<code>IdeDasdChild</code>, <code>IdeDasdExer</code>, <code>IdeTapeExerCmd</code>,~~ the ~~<code>#ide*</code> comms units~~) is the ~~'''Interactive Device Exerciser''' — the DST/SST concurrent~~-~~diagnostics layer —~~ '''not''' ~~a device driver and nothing to do with~~ ATA/IDE. The mainline disk driver that validates a drive against this table is <code>SmDasdValidater</code> / <code>IoHwDevDasd</code>; its SCSI commands go through the shared SIOA layer (see [[System Internals:SLIC SCSI storage subsystem (SIOA)]]).		* "Ide" in SLIC symbol names (e.g. the driver classes handling these disks) is the disk device-driver namespace, '''not''' ATA/IDE.
	* Numbers like 2748, 6502, 6512, 6751, 6753, 6754 that appear on other SLIC symbols are IOP / disk-controller CCINs, not drive models.		* Numbers like 2748, 6502, 6512, 6751, 6753, 6754 that appear on other SLIC symbols are IOP / disk-controller CCINs, not drive models.
	* An emulated target (for example on open SCSI-emulator firmware) must present one of the vendor+product pairs above verbatim, space-padded to the SCSI field widths, implement the vendor-unique SKIP commands, and report a legal capacity via <code>READ CAPACITY</code>.		* An emulated target (for example on open SCSI-emulator firmware) must present one of the vendor+product pairs above verbatim, space-padded to the SCSI field widths, implement the vendor-unique SKIP commands, and report a legal capacity via <code>READ CAPACITY</code>.

	[[Category:System Internals]]		[[Category:System Internals]]

Friedkiwi: Correct the Ide note: Ide = Interactive Device Exerciser, not the driver; add SIOA/tape cross-ref (via update-page on MediaWiki MCP Server)

2026-08-15T18:57:53Z

Correct the Ide note: Ide = Interactive Device Exerciser, not the driver; add SIOA/tape cross-ref (via update-page on MediaWiki MCP Server)

← Older revision		Revision as of 20:57, 15 August 2026
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	== Notes ==		== Notes ==

	* "Ide" in SLIC symbol names (~~e.g.~~ the ~~driver classes handling these disks~~) is the ~~disk device~~-~~driver namespace,~~ '''not''' ATA/IDE.		* "Ide" in SLIC symbol names (<code>IdeDasdChild</code>, <code>IdeDasdExer</code>, <code>IdeTapeExerCmd</code>, the <code>#ide*</code> comms units) is the '''Interactive Device Exerciser''' — the DST/SST concurrent-diagnostics layer — '''not''' a device driver and nothing to do with ATA/IDE. The mainline disk driver that validates a drive against this table is <code>SmDasdValidater</code> / <code>IoHwDevDasd</code>; its SCSI commands go through the shared SIOA layer (see [[System Internals:SLIC SCSI storage subsystem (SIOA)]]).
	* Numbers like 2748, 6502, 6512, 6751, 6753, 6754 that appear on other SLIC symbols are IOP / disk-controller CCINs, not drive models.		* Numbers like 2748, 6502, 6512, 6751, 6753, 6754 that appear on other SLIC symbols are IOP / disk-controller CCINs, not drive models.
	* An emulated target (for example on open SCSI-emulator firmware) must present one of the vendor+product pairs above verbatim, space-padded to the SCSI field widths, implement the vendor-unique SKIP commands, and report a legal capacity via <code>READ CAPACITY</code>.		* An emulated target (for example on open SCSI-emulator firmware) must present one of the vendor+product pairs above verbatim, space-padded to the SCSI field widths, implement the vendor-unique SKIP commands, and report a legal capacity via <code>READ CAPACITY</code>.

	[[Category:System Internals]]		[[Category:System Internals]]

Friedkiwi: New page: how OS/400 SLIC recognises SCSI DASD, with the V4R4 accept-table decoded (via create-page on MediaWiki MCP Server)

2026-08-15T18:49:49Z

New page: how OS/400 SLIC recognises SCSI DASD, with the V4R4 accept-table decoded (via create-page on MediaWiki MCP Server)

New page

The '''SLIC DASD device recognition''' table is the static list, inside the OS/400 Licensed Internal Code (SLIC), of which SCSI disk drives the system will accept as a DASD (disk) unit. This page describes how that recognition works, how to find and decode the table in a SLIC image, and — as a worked example — the complete list a V4R4 machine accepts. The method generalises to any release and to other SLIC device tables.

Understanding it matters for preservation: OS/400 refuses ordinary SCSI disks, so keeping a machine alive after a disk failure means presenting a drive (real or emulated) that answers the SCSI bus the way SLIC expects.

== How SLIC decides a disk is acceptable ==

A disk becomes an eligible DASD unit only if it passes three independent gates, all implemented in the SLIC disk device driver:

# '''SCSI INQUIRY must match a static table.''' SLIC compares the drive's INQUIRY vendor id (bytes 8–15) and product id (bytes 16–31) against a built-in table. Only IBM-badged units qualify: the vendor id is normally <code>IBMAS400</code> (a handful of early units use <code>IBM␠␠␠␠␠</code> and two OEM units use <code>QUANTUM␠</code>). An off-the-shelf drive reports its own vendor and is rejected. This is exactly what the "custom firmware" on IBM's 660x/671x disks does: IBM reflashed standard Ultrastar/Corsair mechanisms to answer INQUIRY with an IBM vendor id and an IBM product id.
# '''Vendor-unique SKIP READ / SKIP WRITE.''' The driver issues IBM vendor-unique SCSI commands that read or write a run of sectors while skipping masked ones, used by the Single-Level Store paging path. A faithful drive must implement these, not just standard READ/WRITE.
# '''Capacity from VPD.''' The unit's size is taken at run time from the drive's Vital Product Data / <code>READ CAPACITY</code>, not from the table — the table has no capacity column. An impersonating drive must report a capacity that is legal for the feature type it claims.

== Finding and decoding the table ==

In a SLIC image the table is a run of fixed-size records. On V4R4 each record is 40 bytes:

<pre>
bytes 0- 3 feature type EBCDIC digits, e.g. F6F6F0F7 = "6607"
bytes 4- 5 model EBCDIC, e.g. "1 "
byte 6 class flag 0x00 normal; 0x80 on the 18 GB Ultra2/LVD units
bytes 7-15 reserved 0x40 (EBCDIC space) padding
bytes 16-23 INQUIRY vendor ASCII, matched against INQUIRY bytes 8-15
bytes 24-39 INQUIRY product ASCII, matched against INQUIRY bytes 16-31
</pre>

The type and model are EBCDIC (digit ''n'' = byte <code>0xF''n''</code>); the INQUIRY strings are ASCII. To locate the table, search the image for the ASCII vendor strings <code>IBMAS400</code> / <code>QUANTUM␠</code>: the records sit at a fixed 40-byte stride around them. The same trick — anchor on a known ASCII string, then read the fixed-width record around it — recovers other SLIC hardware tables (IOP/controller CCIN tables, adapter tables, and so on).

== The V4R4 list ==

Every drive a V4R4 system accepts, decoded from the image. "Physical drive" is identification from IBM/Quantum model nomenclature, not read from the binary; the feature type, model and INQUIRY strings are.

{| class="wikitable"
! Feature/Model !! INQUIRY vendor !! INQUIRY product !! Physical drive
|-
| 6109 / 0 || <code>IBM␠␠␠␠␠</code> || <code>0663H12</code> || IBM 0663 "Corsair", ~2 GB
|-
| 6109 / 1 || <code>IBM␠␠␠␠␠</code> || <code>0661371</code> || IBM 0661 "Pixie", ~0.37 GB
|-
| 6105 / 0 || <code>IBM␠␠␠␠␠</code> || <code>0661467</code> || IBM 0661 "Pixie", ~0.47 GB
|-
| 6107 / 0 || <code>IBMAS400</code> || <code>0664M1H</code> || IBM 0664 "Corsair-4", ~4 GB
|-
| 6603 / 0 || <code>IBMAS400</code> || <code>0664N1H</code> || IBM 0664 "Corsair-4", ~4 GB
|-
| 6603 / 1 || <code>IBMAS400</code> || <code>0662S12</code> || IBM 0662 "Corsair", ~1.2 GB
|-
| 6602 / 0 || <code>IBMAS400</code> || <code>0662SW1</code> || IBM 0662 "Corsair", ~1.0 GB
|-
| 6602 / 1 || <code>IBMAS400</code> || <code>DFHSS1W</code> || IBM Ultrastar XP, ~1 GB
|-
| 6605 / 1 || <code>IBMAS400</code> || <code>DFHSS2W</code> || IBM Ultrastar XP, ~2 GB
|-
| 6606 / 1 || <code>IBMAS400</code> || <code>DFHSS4W</code> || IBM Ultrastar XP, ~4 GB
|-
| '''6607 / 1''' || <code>IBMAS400</code> || <code>DCHS09W</code> || IBM Ultrastar 2XP, ~9 GB
|-
| 6713 / 1 || <code>IBMAS400</code> || <code>DGHS18U</code> || IBM Ultrastar 18XP, ~18 GB
|-
| 6714 / 1 || <code>IBMAS400</code> || <code>DGVS09U</code> || IBM Ultrastar 9ES/9LZX, ~9 GB
|-
| 6717 / 1 || <code>QUANTUM␠</code> || <code>SSQD107</code> || Quantum, ~10.7 GB
|-
| 6730 / 0 || <code>QUANTUM␠</code> || <code>SSQD160</code> || Quantum, ~16.0 GB
|-
| 6731 / 0 || <code>IBMAS400</code> || <code>DRVS18D</code> || IBM Ultrastar 18ES/18LZX, ~18 GB, Ultra2/LVD
|}

Feature-type numbers do not track capacity linearly: the type encodes the AS/400 usable-capacity class (after 520-byte-sector overhead), not the drive's native size. The much-cited 6607 is here as <code>IBMAS400</code> / <code>DCHS09W</code>.

== Notes ==

* "Ide" in SLIC symbol names (e.g. the driver classes handling these disks) is the disk device-driver namespace, '''not''' ATA/IDE.
* Numbers like 2748, 6502, 6512, 6751, 6753, 6754 that appear on other SLIC symbols are IOP / disk-controller CCINs, not drive models.
* An emulated target (for example on open SCSI-emulator firmware) must present one of the vendor+product pairs above verbatim, space-padded to the SCSI field widths, implement the vendor-unique SKIP commands, and report a legal capacity via <code>READ CAPACITY</code>.

[[Category:System Internals]]