|1969||Memorex 660-1 Disk Drive (OEM 2314)|
|The establishment of the Original Equipment Manufacture (OEM) disk drive industry decoupled from IBM wherein there were multiple suppliers of compatible disk drives to multiple system's integrators and/or systems manufactureres|
Why it's important
Prior to the existence of interface standards OEM sales were small and typically customized for a systems manufacturer. This family of interfaces for the early DEC RP-0x series of drives (RP01 thru RP03) became the first standard OEM disk drive interface of which there were multiple suppliers selling to both systems manufacturers and systems integrators. DEC chose not to make their low level drive interface face proprietary and it rapidly became the industry standard, going thru several iterations until ultimately low level drive interfaces were obsoleted by intelligent interfaces such as SCSI and ATA/IDE.
The second disk drive company, Bryant was only an OEM. Little is known about its interfaces but they are believed to have been customized for each of its customers.
CDC was also an early entrant into the OEM disk drive market with a 2311 type disk drive, circa 1965. Under Tom Kamp, CDC pursued a strategy of forming relationships with other system companies in order to achieve lower cost thru volume learning. [KAMP80]. It is believed that the interfaces were proprietary between CDC and its customers. At least one version is believed to have been plug compatible with the IBM 2311.
Because there are no known substantive offering of drives compatible to these early Bryant and CDC products they are not considered iconic of the OEM disk drive industry.
DEC RP02 was manufactured by Memorex and offered to OEMs as the Memorex 660-1 beginning early 1969. The interface was a two cable interface, a bus tag cable for control and a data cable with bit serial data. The interface is very similar to the IBM 2314 with the major changes being the use of TTL signaling and the simplification of the tags. Because of the interface changes the drive was not plug compatible with the IBM 2314 family and because of formatting choices the media was not directly pack interchangeable with IBM. Thus this marks the beginning of the disk drive industry departure from strictly adhering to IBMs direction.
DEC, unlike other systems manufacturers, did not assert any proprietary rights to this interface so other OEMs disk drive companies adopted the same interface, both to sell to DEC and to other systems manufacturers and integrators as a standard interface. Minor changes were made to the interface for each generation of disk drive, principally to allow for additional bus bits corresponding to additional cylinders on the later higher capacity drives and for the higher data rates.
Disk drive companies believed to have offered compatible drives with this interface or a variant thereof include Ampex, Century Data Systems (Calcomp), ISS (Information Storage Systems) and Memorex. Potential customers were all of the small minicomputer manufacturers, e.g., DEC and other small systems manufacturers, e.g., Mohawk Data Sciences [DatM71]. An early system's integrator was Telefile circa 1972 [DatM72]. DEC was the largest OEM customer purchasing the RP02 from Memorex and the RP03 from ISS.
These OEM 2314 disk drives used media that was very similar to the IBM 2316 disk pack for the IBM 2314 but differed in details such as the number of sectors and recording format such that in practice there was no media interchangeability with IBM manufactured subsystems.
Shortly after the shipment of the Memorex 660-1, other OEMs began introducing disk drives using the single disk 2315 cartridge, including in order products shipped by Iomec (late 1969 to General Automation), CMD (early 1970 to DEC), and Diablo (mid 1970 to DEC), with Diablo becoming the dominant manufacturer in the early 1970s. At this point it is a research project to determine how different the Iomec interface was from the IBM 2310 disk drive. The Diablo interface is likely quite different in that it uses one flat cable containing both data and control signals. However, in both Iomec and Diablo the serial bit signaling was a higher level clocked signaling (NRZ) as opposed to the self clocking signalling (FM) used in the 2314 class of product. This NRZ signaling was used in the first disk drive, the RAMAC.
In 1971 ISS was first of several OEM 2314 disk drive vendors to introduce a double capacity version achieved by doubling the track density. This is likely the first disk medium that could not be made readable by an IBM manufactured subsystem.
The interface of the highly successful SMD drive family of the late 1970s was a variant of the DEC interface mainly distinguished by changing the serial bit signaling interface to the higher level protocol as used in the 2315 cartridge class of drives.
Bus/Tag interfaces with bit serial data continued to be developed into the 1990s with ESDI (Enhanced Small Device Interface) achieving ANSI approval (ANSI X3.170-189) and being reaffirmed in 1994 noting "some vendors are still shipping ESDI products." [ANSI94]
[ANSI94] ANSI X3T10 document X3T10/94-127r0, available by searching T10 Document Register
[DatM71] Datamation, Nov 15, 1971, "Mohawk To Introduce Shared Processor" [using CalComp disk drive], p. 7
[DatM72] Datamation, Sept 1972, Advertisement for Telefile Controller
[KAMP80] Oral history interview with Thomas G. Kamp
Provenance note: This article was authored by Tom Gardner; his last approved revision is Version 13.