Universal Disk Drive Type Emulation for IBM PC-AT Computers

1. Field of the Invention

The present invention relates to hard disk file storage systems. More particularly, the present invention relates to a disk drive in a hard disk file data storage system.

2. Description of the Prior Art

Disk file data storage systems contain one or more magnetic disks on which data is stored in sectors which lie in concentric tracks on the disks. A transducer (or head) flies above a track and writes, or magnetically encodes, the data in a sector on the track. The head is also capable of reading the magnetically encoded data from the sectors.

An electromechanical actuator operates within a negative feedback, closed-loop servo system. The actuator moves the head radially for track seek operations and holds the transducer directly over a track for track following operations.

Typically, a file of disks is stacked on a spindle. Each surface on each magnetic disk has one corresponding head. All heads are moved together by the electromechanical actuator to different tracks on the disk surface. The collection of the tracks under all heads at any given radial position along the disk file is known as a cylinder. Data read from the sectors by the heads is demodulated in a disk drive interface and provided to a host computer.

In the past, serial or classical disk drive interfaces, such as the ESDI or ST506 interfaces demodulated the data read from the track on the magnetic disk and provided it in serial form. An additional component, known as a disk drive controller, checked the integrity of the data provided by the serial disk drive interface and converted the serial flow of data into a parallel flow. The parallel information was then provided by the disk drive controller to a host computer.

More recently, disk drive interfaces have been designed with more intelligence than the classical or serial disk drive interfaces. Examples of such intelligent disk drive interfaces are the SCSI and PCAT (which was invented based on the PC-AT computer design) interfaces. Functionally, these intelligent interfaces and the disk drive controller have become part of the disk drive and provide parallel data to the host computer

Most PC-AT type host computers are programmed to operate with a number of specific disk drive types. The PC-AT type host computer contains a table of disk drive types which it will operate with. That table contains the number of cylinders, heads and sectors per track for each drive type entered in the table. This table is fixed in the Basic Input/Output System (BIOS) ROM.

A power up program located in the BIOS ROM provides the disk drive controller with the disk drive parameters, from the table, which correspond to the drive type that the host computer is programmed for. The disk drive controller then configures itself to match the table entry corresponding to the disk drive parameters provided by the power up program.

All disk drive types included in the table in the PC-AT type computer use a sector number of 17 sectors per track with a specific number of heads and cylinders.

The fixed table imposes a limitation on the maximum disk drive capacity that the lost computer can access. This is an increasing problem with the advances being made in enlarging disk capacity.

The computer typically addresses the disk drive through BIOS calls. Presently, typical BIOS programs allow up to 1024 cylinders, 16 heads and 64 sectors per track to be addressed Hence, the maximum disk drive capacity addressable by BIOS is 1,048,576 blocks (536,870,912 bytes). But, if the computer cannot address more than 17 sectors per track because of the inflexible disk drive type table, the addressable disk drive capacity is cut down to 278,528 blocks (142,606,336 bytes).

In the present invention, a disk drive is configured for use in a data storage system of the type having a computer coupled to the disk drive for storing data on storage media in a disk drive and for retrieving data from the storage media in the disk drive. The storage media has a physical storage capacity. A plurality of first logical drive address parameters are received from the computer. Second drive address parameters are determined based on the first logical drive address parameters and the physical configuration of the storage media. The disk drive is controlled as a function of the first and second logical drive address parameters.

FIG. 1 is a block diagram of a data storage system.

FIG. 2 is a top view of a disk in the data storage system shown in FIG. 1.

FlG. 3 is a more detailed block diagram of the host computer shown in FIG. 1.

FIG. 4 shows the calculations performed by the disk drive controller to emulate the drive type expected by the host computer.

FIG. 5 shows calculations performed by the disk drive controller to access information in the disk file.

FIG. 6A illustrates the concept of a logical block address.

FIG. 6B illustrates the mathematical calculation of a logical block address .

1. Introduction

FIG. 1 is a block diagram of hard disk file data storage system 10 (data storage system 10). Data storage system 10 includes host computer 12 and disk drive 14. Disk drive 14 includes drive controller 16, conditioning logic 18, actuator 20 transducers or read/write heads 22, 24, 26, 28, 30, 32, 34, 36, 38 and 40 (heads 22--40), magnetic disks 42, 44, 46, 48 and 50 (disks 42-50) and spindle 52.

During operation, disks 42-50 spin with spindle 52. Heads 22-40 fly above disks 42-50 either reading magnetically encoded data from the surfaces of disks 42-50 or encoding (writing) information on the disk surfaces While reading information, heads 22-40 produce signals representative of the data on the disk surfaces and provide those signals to conditioning logic 18. Conditioning logic 18 conditions the signals and provides them in serial form to drive controller 16. This flow of information from heads 22-40 to drive controller 16 is indicated by arrows 54 and 56.

Drive controller 16, in turn, converts the serial data received from conditioning logic 18 into parallel data and provides it to host computer 12. Drive controller 16 also receives control information from host computer 12. Based on that control information and position error information read from disks 22-40, drive controller 16 provides control signals to conditioning logic 18 and actuator 20. This is indicated by arrows 58 and 60.

The control signals provided by drive controller 16 to conditioning logic 18 dictate, for example, which head conditioning logic 18 should demodulate and provide to drive controller 16. The control signals provided to actuator 20 cause actuator 20 to rotate. Rotation of actuator 20 causes heads 22-40 to move radially with respect to disks 42-50.

FIG. 2 shows a typical disk surface. The surface of disk 42 contains a plurality of tracks. For clarity, only two tracks, 62 an 64 are shown in FIG. 2. Each track on the surface of disk 42 is divided into sectors. The sector divisions on track 62 are indicated by the radially oriented cross hatched lines 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99, and 101. Head 22 is shown positioned over sector 68 of track 62 on disk 42. As disk 42 rotates in the direction indicated by arrow 66, head 22 flies above track 62 and data is read from or written to track 62. As actuator 20 moves heads 22-40, head 22 moves radially with respect to disk 42 in an arc indicated by arrow 70. All heads are moved together as actuator 20 rotates. Therefore, heads 22-40 are simultaneously moved over corresponding tracks on each disk as actuator 20 rotates. The collection of tracks under heads 22-40 at a given radial position is known as a cylinder. Therefore, the number of cylinders and the number of tracks per surface on disks 42-50 is the same. Also, the number of tracks per cylinder is the same as the number of heads 22-40 in disk drive 14.

An individual data sector on one of disks 42-50 is addressed by its cylinder address, head address and sector number. The term "address" implies a number in a sequence starting with 0. The term "number" implies a number in a sequence starting with 1. For example, the first sector available in disk drive 14 is addressed as cylinder 0, head 0 and sector 1. Hence, when host computer 12 wants to access a particular sector or sectors on one of disks 42-50, it specifies to drive controller 16 the requested sector number, head address and cylinder address. Drive controller 16, in turn, causes actuator 20 to move heads 22-40 to the correct cylinder. Drive controller 16 also causes conditioning logic 18 to demodulate information from the correct head.

FIG. 3 is a more detailed block diagram of host computer 12. Host computer 12 includes CPU 72, CMOS RAM 74 and BIOS ROM 76.

If host computer 12 is a typical PC-AT type computer, it contains a table of disk drive types which is fixed in the BIOS ROM. The table defines the number of cylinders, heads and sectors per track for each drive type in the table. During power up, a BIOS power up program causes CPU 72 to send drive controller 16 drive parameters which correspond to one of the drives in the table. The drive parameters correspond to the drive type which host computer 12 expects to be installed. The drive parameters sent to drive controller 16 typically include the maximum number of sectors per track and the maximum head address that host computer 12 expects to access during operation.

When the physical parameters of disk drive 14 exactly match the parameters sent by host computer 12 upon power up, disk drive 14 is said to be operating in the physical mode. However, more typically, the actual physical parameters of disk drive 14 differ from those expected by host computer 12. In that case, disk drive 14 is said to be operating in the logical mode. In the logical mode, it becomes necessary to convert a logical data sector address specified by host computer 12 into the actual or physical data sector address that can be accessed by drive controller 16.

In other words, in the physical mode, host computer 12 recognizes the actual number of cylinders, heads and sectors per track in disk drive 14 and addresses them with the proper physical address In the logical mode, on the other hand, drive controller 16 must convert logical addresses provided by host computer 12 into actual, physical addresses in disk drive 14.

In order for the entire physical storage capacity of disk drive 14 to be utilized, two things must be done First, disk drive 14 must be initialized based on the logical disk drive parameters provided by host computer 12 from the table of disk drives stored in the BIOS ROM and based on the physical storage capacity of disk drive 14. Second, disk drive 14 must actually accept logical addresses from host computer 12 and convert them into physical addresses so that the proper data can be accessed on disks 42-50.

2. Initialization

The initialization phase is essentially a four step process These steps are illustrated in FIG. 4. First, drive controller 16 receives the logical drive address parameters from the table in BIOS ROM 76 of host computer 12 The logical drive address parameters typically include the maximum number of logical sectors per track and the maximum logical head address that host computer 12 expects to access

Second, drive controller 16 calculates the number of logical sectors per logical cylinder This is done by multiplying the number of logical heads, provided by host computer 12, by the number of logical sectors per track, which is also provided by host computer 12. This result (result A) is then saved.

Third, controller 16 computes the total number of physical sectors in disk drive 14 (the total physical storage capacity of disk drive 14). This is done by multiplying the number of physical sectors per cylinder, which is stored in memory in drive controller 16, by the number of physical cylinders in disk drive 14, which is also stored in memory in drive controller 16. This result (result B) is then saved

Finally, drive controller 16 calculates the maximum logical cylinder address required to utilize the entire physical storage capacity of disk drive 14. (Note that the maximum logical cylinder address was not provided by host computer 12 during power up). The maximum logical cylinder address is calculated by dividing the total number of physical sectors in disk drive 14 (result B) by the number of logical sectors per logical cylinder (result A). At this point, drive controller 16 has stored the number of logical sectors per track and the maximum logical head address that the computer expects to access, as well as the number of logical sectors per cylinder and the maximum logical cylinder address that the computer may access. All of these values are saved and used in the conversion phase.

3. Conversion

Once the initialization phase has been performed, disk 14 is prepared to accept commands from host computer 12 requiring drive controller 16 to access or locate information on disks 42-50. The commands from host computer 12 typically include the logical cylinder address, logical head address, logical sector number and number of sectors to be accessed by host computer 12 as well as a command code. Typical command codes include Read, Write and Verify operations.

Drive controller 16 must convert the logical addresses and numbers provided by host computer 12 into corresponding physical addresses and numbers in order to access the proper data on disks 42-50. This conversion is essentially done in four steps and is shown in FIG. 5.

First, drive controller 16 calculates a logical block address corresponding to the information to be accessed by host computer 12. FIGS. 6A and 6B illustrate the concept of a logical block address The logical block address uniquely identifies each individual sector in disk drive 14. The logical block address identifies the first sector in disk drive 14 as sector 0 and each subsequent sector is identified by a sequentially increasing address ending with the very last sector on the very last cylinder and corresponding to the very last head address.

For example, FIG. 6A shows a data storage system where the heads are positioned over cylinder 0. There are 36 physical sectors per track under each head. Therefore, heads 0, 1, 2 and 3 are each over tracks which have 36 sectors. The physical sector numbers are shown within the track in FIG. 6A and go from 1 to 36 in each track. However, the logical block address does not start at 1 with each new track. Rather, the logical block address starts at 0 for sector 1 of head 0 and cylinder 0 and simply increases sequentially from the first sector to the last in the disk drive. Hence, as shown in FIG. 6A, where a data storage system has only one cylinder and four heads, and where there are 36 physical sectors per track in the data storage system, the maximum logical block address is 143. The logical block addresses for the sectors shown in FIG. 6A are indicated in parenthesis below the physical sector number of each sector.

The logical block address is calculated as shown in FIG. 5. The product of the logical cylinder address from host computer 12 and the number of logical sectors per cylinder is added to the product of the logical head address from host computer 12 and the number of logical sectors per track. This, in turn, is added to the logical sector address from host computer 12. As an example, the logical block address for physical sector number 33 of head 0 in FIG. 6A is calculated in FIG. 6B.

Once the logical block address is calculated, drive controller 16 calculates the physical cylinder address corresponding to the logical address provided by host computer 12. The physical cylinder address is calculated by dividing the logical block address by the number of physical sectors per cylinder. That division yields the physical cylinder address plus remainder 1.

Next, the physical head address is calculated This is done by dividing remainder 1 by the number of physical sectors per track. This division yields the physical head address plus remainder 2.

Finally, the physical sector address is determined. The physical sector address equals remainder 2. Each logical address provided by host computer 12 is converted to a physical address in this manner. This allows host computer 12 to access the entire physical storage capacity of disk drive 14.

Drive controller 16 accepts any value for any combination of logical cylinders, logical heads or logical sectors per track and calculates the remaining parameters to initialize disk drive 14 for utilization of the entire physical storage capacity of disk drive 14. Drive controller 16 even accepts logical parameters which are greater than its physical parameters. This allows disk drive 14 to configure itself to emulate any disk drive type which happens to reside in the table in BIOS 76 or any other drive type.

Further, the present invention removes existing capacity access limitations. Since drive controller 16 accepts any value for logical address parameters, it is not limited to emulating disk drives having a maximum of 17 sectors per track. Nor is it limited to the number of cylinders, heads and sectors per track currently contained in power up programs in BIOS. Additionally, should the address capacity in BIOS change, disk controller 16 will accommodate the changes without redesign. Hence, the BIOS address limitations and the conventional 17 sector per track limitation are effectively removed.

For these reasons, the software used in drive controller 16 will not require any redesign for implementation in future disk drives which are designed with larger physical storage capacities. Nor would any redesign be required if users insert drive parameters in the table in BIOS ROM 76 which have not been previously included in that table.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.