ML11 MOS Memory System

The ML11 was a MASSBUS solid state mass storage device. Its basic format was 18-bit words (for use in PDP-10 and PDP-15 machines), but it could be used in PDP-11s and VAXen, which simply ignored the two high bits.

It attached to any MASSBUS controller, e.g. RH11 (UNIBUS), RH70, or RH780. Up to 8 devices total can be attached to any MASSBUS controller.

The initial configuration, using 16Kbx1 DRAM chips, could hold up to 4MB in 1MB increments (composed of groups of 4 storage modules); later, the use of 64Kbx1 chips expanded the maximum to 16MB. An ML11 with the former was denominated as an ML11-A; with the latter, as an ML11-B.

The memory was organized in 36-bit words, with 3 bits per word added to hold a CRC ECC.

Registers

In the table below, 'Number' is the MASSBUS register number; the 'Address' is the UNIBUS address (e.g. when using an RH11).

Location	Number	Name	Function
000	00	MLCS1	Control and Status 1
002		MLWC	Word Count
004		MLBA	Bus Address
006	05	MLDA	Desired Address
010		MLCS2	Control and Status 2
012	01	MLDS	Drive Status
014	02	MLER	Error
016	04	MLAS	Attention Summary
020	07	MLPA	PROM Address
022		MLDB	Data Buffer
024	03	MLMR	Maintenance
026	06	MLDT	Drive Type
030	010	MLSN	Serial Number
032	011	MLE1	ECC CRC Word 1
034	012	MLE2	ECC CRC Word 2
036	013	MLD1	Data Diagnostic 1
040	014	MLD2	Data Diagnostic 2
042	015	MLEE	ECC Error
044	016	MLEL	ECC Location
046	017	MLPD	PROM Data
050		MLBAE	Bus Address Extension@
052		MLCS3	Control and Status 3@

@ = RH70 only, not RH11

The addresses shown are based at 0776400 for the first ML11 in a system.

Implementation

The basic system consisted of a number of hex boards mounted in a custom 22-slot backplane (DEC part number 70-17508), all housed in a BA11-K mounting box. The basic device controller boards were:

• M7361 asynchronous control module
• M7362 synchronous control
• M7363 array data module

Initially, data storage was provided with M7357 boards, used in groups of four, each board holding 256KB; later, these were supplanted by M7358 boards, each board holding 1MB.

Three dual-width M5903 boards provided the MASSBUS interface; flat cables led from Berg connector headers on the M5903's to the MASSBUS controller.

Board locations (as seen from the board insertion side of the backplane, not the wire-wrap pin side, as is common in DEC documentation) are:

	Connector
Slot	A	B	C	D	E	F
1	Unused		M5903 MASSBUS		Unused
2	Unused		M5903 MASSBUS		Unused
3	Unused		M5903 MASSBUS		Unused
4	M7361 asynchronous control
5	M7362 synchronous control
6	M7363 array data
7	M7357/58 arrray board 0
8-21	Arrray boards 1-14
22	M7357/58 arrray board 15

Further reading

• ML11 User's Guide (EK-0ML11-UG) - not available online
• ML11 Technical Description (EK-0ML11-TD) - not available online
• ML11 MOS Memory System Technical Manual (EK-0ML11-TM-002) - not available online, but in microfiche
• ML11 MOS Memory System Technical Manual (EK-ML11A-TM-003) - not available online, but in microfiche
• ML11 MOS Memory System Service Guide (EK-ML11A-SV-001) - not available online, but in microfiche