Data processing: database and file management or data structures – Database design – Data structure types
Reexamination Certificate
1999-09-30
2003-06-10
Mizrahi, Diane D. (Department: 2775)
Data processing: database and file management or data structures
Database design
Data structure types
C360S053000
Reexamination Certificate
active
06578034
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
(Claiming Benefit Under 35 U.S.C. 120)
None.
FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT STATEMENT
This invention was not developed in conjunction with any Federally sponsored contract.
MICROFICHE APPENDIX
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to the arts of persistent and non-volatile computer data storage and the organization of the devices thereof. In particular, this invention relates to the art of assignment of drive letters which travel with the computer data storage media, including removable hard disk drives and removable optical drives.
2. Description of the Related Art
Persistent and mass data storage devices for computer systems, especially those employed in personal computers, are well known within the art. Many are disk-based, such as floppy disks, removable hard disk drives (“HDD”), and compact-disk read only memories (“CD-ROM”).
FIG. 1
shows a typical personal computer system (
1
) architecture, wherein a CPU (
2
) interfaces to a variety of I/O devices such as a keyboard (
3
), monitor or display (
5
) and a mouse (
4
). The CPU (
2
) also may interface to a number of storage peripherals including CD-ROM drives (
7
), hard disk drives (
6
), and floppy drives (
5
). Typically, floppy disk drives interface to the CPU via Integrated Drive Electronics (“IDE”) (
8
), but this interface may alternately be one of several other standard interfaces or a proprietary interface. The hard disk drives (
6
) and CD-ROM drives (
7
) may interface to the CPU (
2
) via an IDE or Small Computer System Interface (“SCSI), as shown (
9
).
FIG. 2
shows a generalization of the hardware, firmware and software organization of a personal computer system (
20
). The hardware group (
21
) includes the persistent storage devices discussed supra, as well as other system hardware components such as a real-time clock, keyboard controller, display adapter, etc. A basic input/output system (“BIOS”) (
22
) provides the direct firmware control of these system components typically. An operating system (
24
) such as the IBM OS/2 operating system provides high level management of the system resources, including the multi-tasking or multi-threaded scheduling and prioritization of the system application programs (
25
). This generalized view of the system also applies to systems on alternate, non-IBM-compatible platforms, such as workstations, which employ a variety of operating systems such as Microsoft Windows or UNIX. This general organization of computer system resources and software functionality is well understood in the art.
Turning to
FIG. 3
, disk-based mass storage devices such as hard disk drives, floppy disks and CD-ROMS are based physically on a rotating storage platter (
30
). This platter may be made of flexible mylar, such as floppy disks, or more rigid platters made of aluminum, glass or plastic, such as hard disk drives and CD-ROMS. For magnetic media, one or both sides of the platter are coated with a magnetic layer capable of recording magnetic pulses from a read/write head. For optical media, data recording is made using changes in reflectivity of a band of light, which is then read by a laser-based head. Writable and Re-writable CD-ROM drives combine the technologies of magnetic disks and optical disks. In general, though, the organization of data on the disk is similar. The disk surfaces are divided into multiple concentric rings, or tracks (
31
). Some disk drives, such as hard disk drives, consist of multiple platters, in which case corresponding tracks on each platter are grouped into cylinders. Each track is divided into multiple sectors (
32
) in which data can be stored.
In order to simplify the formatting and control of disk platters, most DOS-based disk formats use a uniform sector length of 512 bytes within all tracks, with additional header and trailer information in each sector bringing a sector to a total standard length of 571 bytes.
FIG. 4
shows a typical sector breakdown on a track (
31
), including header area (
40
), followed by a 512 byte area for data storage (
41
), and concluded by an area for Error Correction Codes (“ECC”) (
42
). A small gap (
43
) precedes and follows each sector to provide physical separation between the previous sector (
45
) and the succeeding sector (
44
).
As the tracks towards the outer edge of the platter are much longer than the tracks located towards the inner edge or center of the platter, the outer tracks are physically capable of holding more of the equal-length sectors.
Computer disk drives are typically broken into one or more partitions, each of which may be assigned different logical volume or drive letter designations. The partitioning of a physical disk drive is controlled by the partition tables located on it, along with some simple rules which govern where partitions may start and end.
Generally, the rules followed by almost all personal computer operating systems are:
(a) a partition must consist of contiguous disk space,
(b) there may only be 4 partitions on a disk maximum,
(c) the partition table which defines these 4 partitions is part of the Master Boot Record (MBR),
(d) the MBR must always be located in the first sector on the disk,
(e) partitions may be of two types, Primary or Extended,
(f) only one extended partition may exist on a disk,
(g) Primary partitions must always start on cylinder boundaries unless immediately preceded by an MBR, in which case a Primary partition may start on the first track following the MBR,
(h) Extended partitions must always start on a cylinder boundary, and
(i) Partitions, whether Primary or Extended, must end on a cylinder boundary.
To allow more than 4 partitions on a drive, an extended partition can be divided into logical drives. Each logical drive is set up to look like a disk drive, i.e. it's first sector will contain the equivalent of an MBR (called an EBR) which contains a partition table. This partition table defines one primary partition, which is commonly referred to as a “logical drive,” even though it is actually a logical partition. The entire structure consisting of the EBR and the logical partition is the “logical drive”. As with all primary partitions following an MBR or EBR, it will start on the first track following the EBR, and end on a cylinder boundary. If there is more than one logical drive existing in the extended partition, then this partition table will also define an extended partition. As with all extended partitions, this extended partition will start and end on a cylinder boundary. This extended partition entry in the EBR is really just a link to the start of the next logical drive. All of the logical drives defined in an extended partition will have this link in their EBRs, except for the last logical drive. The last logical drive in the chain will have only a primary partition defined in its EBR. Thus, the chain of logical drives in an extended partition may be treated as a linked list.
TABLE 1 shows a view of a typical partition table for a disk having two partitions on a 6 Giga Byte drive which has 255 usable sides and 63 sectors per track.
TABLE 1
Partition Table for 6 GB Drive
Start
End
Length
Partition
(cylinder, side, sector)
(cylinder, side, sector)
(sectors)
first
0, 1, 1
391, 254, 63
6297417
second
392, 0, 1
783, 254, 63
6297480
For the disk partitioning shown in TABLE 1, the MBR is located in the first sector on side
0
at cylinder
0
sector
1
. The MBR requires only one sector, but the entire track of 63 sectors is “blocked” for the use of the MBR, 62 sectors of side
0
cylinder
0
are left unused.
The partitioning rules just discussed have some interesting repercussions, including:
(a) there can be at most 4 primary partitions,
(b) a disk can be partitioned such that there can be as many logical drives as disk space permits,
(c) if one or more logical drives exist, then there can be at most 3 primary partitions,
(d) it is possible to partition a disk such that blocks of disk space are unusable (i.e. they can not be defined
Frantz Robert H.
International Business Machines - Corporation
Mims Jr. David A.
Mizrahi Diane D.
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