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Implementation of the Enhanced Small Device Interface Host Adapter/ Controller for Five and One Quarter Inch Disk Drives

IP.com Disclosure Number: IPCOM000040100D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 4 page(s) / 71K

Publishing Venue

IBM

Related People

Boyd, GA: AUTHOR

Abstract

This article describes a method which allows the attachment of the highest capacity 5-1/4-inch fixed disk drives to low and midrange computing systems. A host Enhanced Small Device Interface (ESDI) adapter is implemented with a generic interface disk data controller chip combined with discrete hardware and microprocessor-controlled parts. The ESDI provides control for low-end direct access storage devices (DASDs) and tape drives. The protocol evolved from the accepted ST-506 interface standard for 5-1/4-inch hard drives; yet it provides a step increase in relative performance and functionality. The ESDI maintains essentially the same physical interface structure as ST-506, but adds a new logical protocol layer to facilitate intelligent drives.

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Implementation of the Enhanced Small Device Interface Host Adapter/ Controller for Five and One Quarter Inch Disk Drives

This article describes a method which allows the attachment of the highest capacity 5-1/4-inch fixed disk drives to low and midrange computing systems. A host Enhanced Small Device Interface (ESDI) adapter is implemented with a generic interface disk data controller chip combined with discrete hardware and microprocessor-controlled parts. The ESDI provides control for low-end direct access storage devices (DASDs) and tape drives. The protocol evolved from the accepted ST-506 interface standard for 5-1/4-inch hard drives; yet it provides a step increase in relative performance and functionality.

The ESDI maintains essentially the same physical interface structure as ST-506, but adds a new logical protocol layer to facilitate intelligent drives. ESDI compatible devices effectively de-couple peripheral bus technology from drive technology. Disk drive densities and transfer rates may increase through the years with no impact on the host adapter, since the adapter will automatically configure itself to the new device parameters. The obvious benefit is one-time development of controller hardware and software of ESDI compatible drives of any vendor, as well as new and higher performing drive models as they become available. There are a great number of support chips which provide and handle the ST-506 interface standard, but no controller chips that provide the ESDI standard directly.

This obstacle is surmounted in the host adapter/controller by dividing the interface signals into three categories, and then implementing each category of signals in the most efficient manner, as follows: 1. Time-critical data sequencer functions, such as serial-to-parallel conversion, error correction code

(ECC) calculations, and track format control that can

be implemented with many generic disk interface

controllers currently on the market. 2. Non-time-critical interface signals, that would require considerable host I/O processor (IOP) overhead to

monitor and control, and thus would be more efficiently

implemented in discrete logic. 3. Non-time-critical interface signals that would require a minimum of IOP overhead, and therefore would not

affect the throughput of an IOP that is shared between

I/O adapters. This method negates the need for a dedicated microprocessor on the host adapter/controller and only requires the IOP to handle those ESDI signals in the third category above. This technique produces an economical implementation of the most advanced interface protocol available for device-level control of 5-1/4-inch disk subsystems. The allocation and definition of the ESDI signals are detailed below. The portion of the ESDI protocol which is related to high-speed data and associated data control signals can be handled by most generic DASD interface controller chips. The controller chip must also contain the ECC function and FIFO buff...