Setup and Benchmarks of Several ESDI Hard Disks and Controller Cards

Twenty-seven controller cards are available and will be tested. For the moment I will divide them in four groups; controller cards for the Industry Standard Architecture (ISA), cards for the Extended Industry Standard Architecture (EISA), cards for the Micro Channel Architecture (MCA), and bridge controller cards for the Small Computer System Interface (SCSI).

Manufacturer	Model	Supported Data Rates (MHz/s)
Adaptec	ACB-2322B	Rev B: 10 Rev C: 10, 15
Adaptec	ACB-2322D	10, 15, 20
Compaq	15MHz ESDI Controller	10, 15
CompuAdd	HardCache/ESDI with 4MB Cache	10, 15
Data Technology	DTC 6280-15T	10, 15
Data Technology	DTC 6282-15Z	10, 15
Data Technology	DTC 6282-24	10, 15, 20, 22, 24
Distributed Processing Technology	DPT PM3011E/75 with 4MB Cache Module	10, 15, 20
Everex	EV-348A	10, 15, 20
National Computer Ltd.	NCL 5355	10
Perceptive Solutions	hyperSTORE 1600 with Cache Expansion Adapter	10, 15, 20
Scientific Micro Systems	Omti 8620	10
Ultrastor	Ultra 12F-32	10, 15, 20, 22
Ultrastor	Ultra 12F-24	10, 15, 20, 22, 24
Ultrastor	Ultra 12C with 16MB Cache	10, 15, 20
Western Digital	WD1005-WAH	5, 10
Western Digital	WD1007V-SE2	10, 15
Western Digital	WD1009V-SE2	10, 15, 20, 22, 24

Manufacturer	Model	Supported Data Rates (MHz/s)
Data Technology	DTC 6290-24 with 4MB Cache	10, 15, 20, 22, 24
Data Technology	DTC 6295-24 with 2MB Cache	10, 15, 20, 22, 24
Ultrastor	Ultra 22C with 0.5MB Cache	10, 15, 20
Ultrastor	Ultra 22CA with 16MB Cache	10, 15, 20, 22, 24
Western Digital	WD1009V-SE2*	10, 15, 20, 22, 24

General ESDI Controller Features

Manufacturer	Model	Supported Data Rates (MHz/s)	Click on Picture to Magnify
IBM	IBM ESDI Fixed Disk Controller	10
Western Digital	WD1007V-MC1	10, 15

Manufacturer	Model	Supported Data Rates (MHz/s)
Adaptec	ACB-4525 S4501	10
Emulex	MD21	15
Scientific Micro Systems	OMTI 7200	10

Early controller cards like the WD1005-WAH couldn't process the data of one formatted track during one revolution of the drive platter. They lacked a sufficient data buffer or the buffer was to slow. If a track can be read during one platter revolution, the sectors of this track are numbered in ascending order. (Otherwise the sectors are numbered in interleaved order.) This technology is called one-by-one interleave. A one-by-one interleave is a prerequisite to achieve a high data throughput.
Later controller models got a track cache, which allowed the controller to read ahead an additional track and to store the data in a hardware cache. Now the track data was stored in SRAM or VRAM ICs, which allowed data access in the nanosecond range and data throughput only limited by the system bus bandwidth.

Another feature of ESDI controller cards is the ability to circumvent limitations of the IBM BIOS for hard disk storage space addressing. The early IBM BIOSs use a table of fixed drive types, all of them with 17 sectors per track. Except for the very few 5MHz models, ESDI hard disks have at least 34 sectors per track. Using an IBM BIOS drive type for such a disk would mean to waste half of the valuable storage space.

Several technologies were developed, to circumvent this dilemma. Basically they translate the physical drive geometry, which consists of the number of cylinders (cyl), the number of heads (hd), and the number of sectors per track, (spt) into a logical drive geometry, which the computer system as well as the operating system is able to understand and use. These technologies are:

* 17-sectors-per-track translation mode
* 32-sectors-per-track translation mode
* 63-sectors-per-track translation mode
* universal translating mode
* 1024 cylinder truncation
* drive splitting
* track mapping mode

For testing purpose we can narrow down to the 63-sectors-per-track translation mode and the track mapping mode. The 63-sectors-per-track mode translates any physical drive geometry into a logical drive geometry up to 1024cyl, 16hd, and 63spt, thus achieving a storage space maximum of 528MB. If the drive has more than 528MB storage space - which is very common for ESDI drives - a track mapping scheme is used, which translates any physical drive geometry into a logical drive geometry up to 1024cyl, 64hd, and 32/63spt, thus achieving a storage space maximum of 1.1/2.1GB (gigabyte). Unless the controller card isn't able to use either, other translation technologies are applied.

ESDI storage offers an advanced defect management. Any magnetic media contains areas where data can't be read or written reliably. The location of these defects are recorded at three different positions on the drive; sector 0 of all tracks of the maximum cylinder (primary or manufacturer defect list), sector 0 of all tracks of the maximum cylinder minus eight (secondary or grown defect list), and sector 0 of all tracks of cylinder 4095 (write protected manufacturer defect list). Every of those sectors holds a record of the corresponding platter surface defects.
The maximum cylinder and the maximum minus eight cylinder can be overwritten accidentally, if the drive is low level formatted e.g. with partitioning software like DiskManager or SpeedStor or with disk utilities like Seagate's sgafmt.exe. Beware: most ESDI controllers will even refuse to detect the drive if the primary defect list is deleted.
ESDI controllers can map defective areas into so called spare sectors. To make use of spare sectors, the user accessible data will be reduced usually for one sector per track. A spare sector is consumed in exchange for a sector in a defective area. Now the drive seems to be error free to the operating system. The tested controllers will not make use this feature unless it is mandatory for a certain controller card.

It depends on the manufacturer and the model how the controller cards performs a low-level-format and how it enables or disables certain features. This will be discussed in the manufacturer setup section.

General Controller Setup

As mentioned earlier, ESDI storage systems overcome certain storage space limitations of the IBM compatible PC. Storage space limits are not always hardware related. Even if the hardware is able to address more than 1024 cylinder, the operating system is probably not. Some 32Bit operating systems like NetWare 386 or certain Unix systems have less problems with this barrier. However, DOS actually has. What this means is, the user has to work with different setup methods, depending on the operating system he wants to make use of. Special problems arise, when more than one operating system should be installed on the hard disk. To keep things neat and easy, we limit the setup to DOS, particularly to DOS versions 4.x and above, because DOS 3.x isn't able to create partitions bigger than 32MB.

There are a few reasons for a DOS test setup. DOS allows unrestricted access to the hardware. As a single task single user operating system measurements are less influenced by other system bus or processor activities.

Standard drive controller cards in a PC have to be compatible with Western Digital's WD1002/WD1003 drive controller card. For our purpose it's enough to know that WD1003-compatibility ensures, that your drive is recognized by the system, if a proper drive type is chosen in the system BIOS.

All ESDI controller cards mentioned here will work in WD1003 compatibility mode. Some offer a native enhanced mode additionally, e.g. all EISA controller cards. To make use of this enhanced mode usually an operating system dependent software driver is necessary. Some cards are able to activate this enhanced mode for the DOS environment through their own BIOS.

To be recognized by the system at boot time, the controller cards must be jumpered correctly. To make things as simply as possible, we assume, the ESDI controller is the only hard disk controller card in the system. If there is a default jumper setting for the card, it exactly reflects this condition. If not, the controller has to be jumpered for:

* primary hard disk port address 1F0-1F7
* enable hard disk controller
* IRQ 14 for hard disk access

Configuring the controller for the secondary port usually will disable it in the 386/486 environment, because system BIOS usually does not support the second channel.

The highest possible data throughput from hard disk platter occurs, when a read/write head process a single track. In case a file is to large for a single track, parts of it may be stored on the same cylinder but on a different platter of the hard drive. The drive electronic has to switch between the read/write heads. As high capacity drives, ESDI Hard disks often employ up to 16 read/write heads. Such a drive is able to process 16 tracks without moving the read/write assembly. While head switch time is rather short, it's not possible for the drive to maintain continuous high data transfer across read/write head boundaries. One main reason for it is the drive spin. When a head switch occurs, several sectors of the following track on the same cylinder pass under the read/write head before it is able to process the data. The head skew reflects the head switch time and shifts the sector number accordingly.
If a file resides across several cylinders the read/write heads have to move on the drive platters. A head move lasts much longer than a head switch. Again a cylinder skew reflects the cylinder- to-cylinder access time and shifts the sector number accordingly. Without head or cylinder skew the platters of a drive have to spin one unnecessary revolution before the drive electronic is able to process the data of the following track.

ESDI Controller usually support head and cylinder skewing. Since head switch time and cylinder-to-cylinder access time differ from drive to drive, the controller has to calculate the best skew factors. Sometimes the manufacturer provide a DOS utility program which calculate skew factors (e.g. Adaptec), when the controller BIOS does not. Early ESDI controller do not calculate the skew factors but rather demand user input.

An other important configuration object is the controller card's BIOS address. The card BIOS provides hard disk preparation and setup routines and it may address the hard disk storage space if the system BIOS has no extended Int13H functions. Without that function there is no support for hard drives with more than 504MB storage space.
The controller should be jumpered for:

In some rare circumstances this area may be used by another ISA adapter card BIOS already. In that case use an alternate address e.g. D800. Note the address setting. It will be of importance later.

There are numerous other configuration settings. Assuming the ESDI controller is the only floppy controller in the system (default configuration) use:

* primary floppy disk address 3F6-3F7
* enable floppy controller
* single speed floppy disk drives
* auto deselect enabled (hard drive LED flashes only if the drive is accessed by the operating system)
* caching enabled

Other jumper configurable controller options are discussed in the manufacturer specific setup.

To complete the physical setup you might want to have a look at the ESDI cabling.

Setup and Benchmarks of Several ESDI Hard Disks and Controller Cards

Controller Cards and General Controller Setup

General ESDI Controller Features

General Controller Setup