INPUT and OUTPUT

INPUT and OUTPUT

• Computers have a wide variety of peripherals

            - Delivering different amounts of data, at different 
              speeds, in different formats

• Many are not connected directly to system or expansion bus
• Most peripherals are slower than CPU and RAM a few are faster
• Word length for peripherals may vary from the CPU
• Data format may vary (e.g., one word might include parity bits)

I/O Modules

• Peripheral communications are handled with I/O modules
• Two major functions:

            - Interface to processor or memory via bus or central link

            - Interface to one or more peripherals via tailored data links

• Typical I/O Module Structure : Communication goes across the bus 

            - CPU checks I/O module device status

            - I/O module returns status

            - If ready, CPU requests data transfer

            - I/O module gets data from device

            - I/O module transfers data to CPU

            - Variations for output, DMA, etc.

• Generic Model of I/O Module 

I/O Module Functions

• Major requirements or functions of an I/O module are 

            - Control & Timing

            - CPU Communication

            - Device Communication

            - Data Buffering

            - Error Detection

I/O Module Decisions

• Hide or reveal device properties to CPU

            - Ex: Disks: LBA (logical block addressing) physical address (CHS) is hidden

              from CPU but older disks expose CHS addressing

• Support multiple or single device

            - Most disk controllers handle 2 devices

• Control device functions or leave for CPU

            - Ex: Video adapters with Direct Draw interface but tape drives expose direct

              control to cpu

• Also O/S decisions

            - Ex: Unix treats everything it can as a file


 Created by,

       AHMAD NUR FATHIN IZZAT BIN AZLI

       B031310273