SCSI BUS seminar topic in computer application.pptx

ertyu

1. SCSI BUS AJAY JANARDHANAN ROLL NO :4

2. SCSI BUS SCSI stands for (small computer system interface) It refers to a standard bus defined by American National Standards The SCSI bus may used to connect a variety of deviceds on a computer. It is well suited with disk drives Specification of scsi standard the devices are connected to a computer via a 50 wire cable

3. . Which can be upto 25 meters in length and can transfer data at rate upto 5 megabytes . SCSI-2 & SCSI-3 have been defined and has many options . Data is transferred either in 8 bits or 16 bits in parallel using clock speeds up to 80 MHZ . The bus may use single-ended transmission . Where is signal uses one wire with a common ground return for all signals . In another option, differential signaling is used with a pair of wires for each signal

4. DATA TRANSFER A SCSI bus can be connected to directly to the processor bus or another standard I/O bus such as PCI ,through a SCSI controller Data and commands are transferred in the form of mutli -byte messages known as packets To send commands or data to a device , the process assembles the information in the memory then instructs the SCSI controller to transfer it to the device When data are read from a device , the controller transfers the data to the memory and then informs processor by raising an interrupt

5. .The SCSI controller contends for control of the SCSI bus . When wins the arbitration process , the SCSI controller sends a commands to the disk controller , specifying the read operation . The disk controller cannot start to transfer data immediately. It first move read head to the disk it sends message to SCSI controller indicates it temporarily suspended Then SCSI bus is now free to be used by other devices . Disk controller sends a command to the disk drives to move the read head to the first sector