CHAPTER6.PPT
- 1. DISKS
- 2. INTRODUCTION • Third Most Important Component. • System Performance ~ Disk Access Frequency • Used Extensively for Virtual Memory. • Disk Critical Applications. 1. Databases. 2. Graphics Oriented Progress. 3. Network Servers. 4. Program Development. • Topics Covered in This Chapter. 1. Hard Disk Installation. 2. Drive Specifications. 3. ST-506. 4. IDE. 5. ESDI. 6. SCSI.
- 3. HARD DRIVE INSTALLATION • The Two Basic Components 1. Hard Disk - (Control Operating Speed & Storage Capacity). 2. Disk Controller - (Controls Speed of Data Transfer). • Special Purpose ROM's 8-bit ISA and 16-bit EISA/MCA Buses. • INTERFACE - Connection Between Two Pieces of Electronic Equipment. • Types of Interfaces. 1. ST - 506/ST - 412 2. SCSI (Small Computer System Interface). 3. IDE (Interface Design Enhancement). • ST - 506 & IDE Are for ISA Bus ISA Based Systems
- 4. DRIVE SPECIFICATIONS • Magnetic Disk Spinning at High Speeds. • Read/write Heads Moving in & Out. • Vacuum Controlled Operation. • Tracks, Cylinders & Sectors • Access Time Is 1. Seek Time. 2. Search Time. 3. Data Transfer Time. • The Average Latency. • Three Important Factors 1. Cylinder Sized. 2. Avg. Access Time. 3. Avg. Latency.
- 5. ST - 506 (NOW OBSOLETE) • The MFM & RLL • Characteristics 1. Introduced With Original IBM PCs & ATs. 2. Very Low Capacity (20 - 80 Mb). • Difference Between MFM & RLL - Data Coding MFM >> 0.75 Flux Reversals/bit. RLL >> 0.25 Flux Reversals/bit • Data Transfer Rates. MFM >> 0.6 M Bytes/sec. RLL >> 0.9 M Bytes/sec. • The St - 506 Interface.
- 6. IDE – Drive Characteristics 1. Fast 2. Large capacities (upto 500MB 3. Easy to install 4. Only two drives with one ISA Bus 5. Cost affective – Controller integrated into the drive – Data transfer rate improvement Theoretical >>6.5MB/S Practical >> 1.2MB/S – Requires mentioning in BIOS setup – May use IDE card in absence of IDE connector
- 7. ESDI – Drive Characteristics 1. High speed 2. Very large capacity (500MB & Beyond) 3. ISA, MCA & EISA bus compatible 4. Cabling & software similar to ST-506 5. Very High Data transfer Rate (4MB/S) 6. Requires definition in BIOS setup
- 8. SCSI – Drive Characteristics 1. General Purpose interface 2. Multiple device connections 3. Large capacities (500MB & Beyond) – May also be used for connecting tape drives, optical drives, CD-ROMs etc. – Standardized Bus using 50-way ribbon cable to chain-connect devices – Two types of external connectors 1. 50-pin connector by Hewlett packard 2. 25-pin connector by apple – Different Imlementation methods 1. SCSI 1 2. Fast SCSI 3. Wide SCSI 4. SCSI 2
- 9. SCSI.....Continued – Each device identification by 1. ID number 2. Logical Unit numbers – Difficult detection of SCSI drive by BIOS – SCSI ROM BIOS on controller – Low level formatting & advanced diagmostic programs do not sure – Advantage : Single controller for many devices – Plug & play approach – May have 5-10MB/S data transfer rate in future.
- 10. ISSUES IN DRIVE SELECTION • Sector Interleave • Track Buffer • Caching Controllers (Elevator Algorithms) • Disk Mirroring • Software Caching (Smart Disk) • RAM Disk • Disk Fragmentation