1 EN0129 PC and Network Technology - 1 Sajjad Shami Adrian Robson Gerhard Fehringer School of Computing, Engineering & Information Sciences Northumbria University Semester One Week 4: Hard Disk Drive HDD [Ref: &

2 Hard Drive Off with the Lid!!!! (Don’t)

3 Detail Platter Head Actuator Arm Voice Coil Actuator Spindle

4 More on Platters/Tracks Most hard drives have more than one Platter –See OLD ONES in Lab Platters are stacked one above the other –The heads fit between the platters –All heads move at the same time –All platters rotate together –At any head position the grouping of the tracks read by each head is termed a cylinder

5 Cylinders Spindle Track on each side Platter 1 Platter 2 Platter 3

6 Sectors One Track Sixteen Sectors ( 63 Sectors common) A sector is the smallest part of Track usable. If not enough data to fill a sector it remains part empty

7 Clusters A group of sectors containing data from a common file

8 Partitions and Formats A new HD must be prepared before it can hold data The HD needs to be –Low level formatted –Partitioned –High level formatted

9 Formatting a HD For a HD Low-level formatting is done by the drive manufacturer Partitioning and High level formatting is left to the user or person installing the drive

10 Low-level formatting Tracks written Sector and inter-sector gaps are written Sector prefix and suffix information is written. Each sectors data area is filled with test pattern data.

11 After Low Level Format Head 1 Head 2 Head 3 Head 4 Head 5 Head 0 Track 0 Cylinder 0 In this case 6 tracks Each track has 63 sectors Many Tracks

12 Partitioning Partitioning separates a single physical hard drives into a number of different areas (drives C: D:) called ‘partitions’ Partitions are allocated a number of cylinders Each partition can hold a particular file system: –FAT, FAT32, HPFS(OS2), NTFS

13 Head 0 Head 1 Head 2 Head 3 Head 4 Head 5 After Partitioning ( FDISK) Primary DOS Partition Extended DOS Partition Active (can be made bootable) DOS allows only one Primary Partition Cannot be active DOS allows only one Extended Partition Many LOGICAL Drives can be made inside the Extended Partition.

14 Why Partition ? Every drive MUST have at least ONE Most Drives have more than one It is at this stage that the Master Boot Record is created –The MBR is the first thing accessed after the POST

15 The Master Boot Record MBR Head 0 Track 0 Sector 1 Sector one, track zero, head zero is where the MBR is stored The MBR stores info re the Partitions. Location Whether active or not This is used to find the boot sector.

16 Location of First Partiton The MBR is located at CHS 001 The first partition starts at CHS 011 Only sector 1 on track 0 head 0 is used Sectors 2 thro 63 are unused. !!!!!!!!! Head 0 Head 1

17 MBR Layout 446 Bytes64 Bytes2 Bytes Initial Program Loader (Bootstrap)4 partition Tables Magic Number ActiveStart CHSStarting SectorTypeEnd CHSNr. of Sectors 1 Byte 3 Bytes4 Bytes 3 Bytes

18 High-level formatting The Operating System writes the: – File-system For FAT file system –Volume Boot Sector (VBS) –File Allocation Table (FAT) –Root directory

19 FORMAT The FORMAT command READS the partition table and gets information about sectors. FORMAT generates the boot sector, writes two File Allocation Tables (FAT) and the root directory. Immediately after format the FAT is filled with 00h (00 hexadecimal) which indicates that the disk does not contain data.

20 Format Format groups the SECTORS into CLUSTERS Files are stored in groups of clusters The FAT stores info about which clusters each files occupies and in what sequence

21 FAT Boot Root directory FAT : 41 41: 42 42: …… other nr’s 62: EOF 103: 62 Example.ext … ……40…