Page 79 - Computer_Science_F5

Computer Science Input and Output systems

Scenario 1.3: Restaurant system for customer service
FOR ONLINE READING ONLY
To understand the concept of input output system in computer architecture, imagine a
restaurant with a well-coordinated system for handling orders, deliveries, and customer
needs. This system is analogous to the Input/Output (I/O) systems in computer
architecture, facilitating communication between the processor (the kitchen) and
external devices (the outside world). Think of Direct Memory Access (DMA) as a
dedicated waiter assigned to handle large food deliveries. DMA allows devices to
transfer data directly between memory and external devices without involving the
processor, improving efficiency for bulk data transfers. Just as the dedicated waiter
frees up the kitchen staff to focus on cooking, DMA frees up the processor for other
tasks. Imagine a fire alarm going off in the restaurant. This unexpected event disrupts
the normal workflow, requiring immediate attention from the staff. Similarly, interrupts
and exceptions are signals from external devices or errors within the system that
require the processor’s immediate attention, temporarily pausing ongoing tasks. To
understand Privileged and Non-Privileged Instructions, imagine only the head chef
has access to the master control panel for adjusting ovens.

This control panel represents privileged instructions, which require a higher level
of access and can only be executed by the operating system or specific programs.
Non-privileged instructions, like those used for basic cooking steps, are accessible to
any program running on the system. The restaurant’s kitchen relies on a well-stocked
pantry and an efficient delivery system to function. Memory acts as the “pantry” for
the processor, storing data and instructions needed for running programs. The I/O
system is like the “delivery system,” handling the flow of data between the processor
and external devices like keyboards, printers, disks, and networks.

Questions:

1. While DMA is great for large deliveries, how would the restaurant handle
individual customer orders from their tables? Is there an analogous concept in
computer I/O systems for dealing with smaller data transfers? Give reasons.
2. Imagine multiple events happening at once - a fire alarm goes off while a large
food delivery arrives. How would the restaurant staff prioritize handling these
urgent situations? How does this relate to the way processors handle interrupts
and exceptions with varying priorities?

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Computer Science Form 5.indd 70 23/07/2024 12:32