Notes - Chapter 0 | Roger Fan

Chapter 0

Created: 2025-12-16

Updated: 2025-12-16

Mainframe Systems

the earliest large-scale computers
- physically massive, often occupying entire rooms
- IO very slow, such as card readers, tape drives, and line printers
Nowadays def: a large system designed for particular tasks, running with massive amounts of data for large organizations like banks, airlines, and government agencies
- reliability, security, and high-throughput
- bulk data processing, enterprise resource planning (ERP), and handling billions of real-time transactions
The Three Stages of Evolution:

Process
- users submit jobs (programs and data) to operators
- operators sort jobs manually (with similar needs) into batches
- OS simply runs each job sequentially (no decision-making)
Features
- One job at a time
- no user interaction
- CPU is often idle, waiting for slow IO devices

Overlaps CPU and I/O → ↑ CPU utilization
Spooling: Simultaneous Peripheral Operations On-Line
- It's only a concept ← implemented by interrupt
- I/O is done with no CPU intervention
- CPU just be notified when I/O is done

Feature	Batch	Multiprogramming	Time-Sharing
System Model	single user, single job	multiple prog.	multiple users, multiple prog.
Purpose	simple	resource utilization	interactive response time
OS feature	N/A	CPU scheduling, memory management	file system, virtual memory, sync, deadlock

multiple CPUs communicate through shared memory
purpose: ↑ throughput, economical, ↑ reliability
SMP (Symmetric Multiprocessing System) -- most popular
- each processor runs the same OS
- require extensive sync to protect data integrity
Asymmetric Multiprocessing System
- each processor is assigned a specific task
- one master CPU & multiple slave CPUs
- for extremely large systems
Multi-core Processors
- on-chip communication is faster than between-chip communication
- problem: different core have different cache
Many-core Processors
- hundreds or thousands of cores
- e.g. GPU (Graphics Processing Unit)
Memory Access Architecture
- UMA (Uniform Memory Access): all processors share the same physical memory uniformly
  - identical access time
- NUMA (Non-Uniform Memory Access): each processor has its own local memory, but can also access memory owned by other processors (higher latency)
  - non-uniform access time

communicate through I/O bus or network
easy to scale to large # of nodes
purpose: resource sharing, load sharing, reliability
architecture:
- client-server model: easy to manage but bottleneck and single point of failure
- peer-to-peer model: each node has equivalent capabilities and responsibilities
Clustered Systems
- multiple systems connected through a high-speed network (e.g. Infiniband)
Supercomputers
- performance measured in FLOPS (Floating Point Operations Per Second), not MIPS (Million Instructions Per Second)

Real-Time OS
- Keep deadline: guarantee response time for critical tasks
- Soft real-time: best-effort to meet deadlines -- priority (e.g. multimedia)
- Hard real-time: must meet deadlines (no/limited secondary storage) (e.g. nuclear power plant)
Multimedia Systems
- a wide range of app: audio, video ...
- timing constraints: 24~30 fps
- on-demand/live streaming: played but not stored
- compression/decompression
Handheld/Embedded Systems
- specialized OS for small devices
- constraints: limited memory, low power consumption, small display, simple I/O

Mainframe Systems

the earliest large-scale computers
- physically massive, often occupying entire rooms
- IO very slow, such as card readers, tape drives, and line printers
Nowadays def: a large system designed for particular tasks, running with massive amounts of data for large organizations like banks, airlines, and government agencies
- reliability, security, and high-throughput
- bulk data processing, enterprise resource planning (ERP), and handling billions of real-time transactions
The Three Stages of Evolution:

Process
- users submit jobs (programs and data) to operators
- operators sort jobs manually (with similar needs) into batches
- OS simply runs each job sequentially (no decision-making)
Features
- One job at a time
- no user interaction
- CPU is often idle, waiting for slow IO devices

Overlaps CPU and I/O → ↑ CPU utilization
Spooling: Simultaneous Peripheral Operations On-Line
- It's only a concept ← implemented by interrupt
- I/O is done with no CPU intervention
- CPU just be notified when I/O is done

Feature	Batch	Multiprogramming	Time-Sharing
System Model	single user, single job	multiple prog.	multiple users, multiple prog.
Purpose	simple	resource utilization	interactive response time
OS feature	N/A	CPU scheduling, memory management	file system, virtual memory, sync, deadlock

Computer system architecture

multiple CPUs communicate through shared memory
purpose: ↑ throughput, economical, ↑ reliability
SMP (Symmetric Multiprocessing System) -- most popular
- each processor runs the same OS
- require extensive sync to protect data integrity
Asymmetric Multiprocessing System
- each processor is assigned a specific task
- one master CPU & multiple slave CPUs
- for extremely large systems
Multi-core Processors
- on-chip communication is faster than between-chip communication
- problem: different core have different cache
Many-core Processors
- hundreds or thousands of cores
- e.g. GPU (Graphics Processing Unit)
Memory Access Architecture
- UMA (Uniform Memory Access): all processors share the same physical memory uniformly
  - identical access time
- NUMA (Non-Uniform Memory Access): each processor has its own local memory, but can also access memory owned by other processors (higher latency)
  - non-uniform access time

communicate through I/O bus or network
easy to scale to large # of nodes
purpose: resource sharing, load sharing, reliability
architecture:
- client-server model: easy to manage but bottleneck and single point of failure
- peer-to-peer model: each node has equivalent capabilities and responsibilities
Clustered Systems
- multiple systems connected through a high-speed network (e.g. Infiniband)
Supercomputers
- performance measured in FLOPS (Floating Point Operations Per Second), not MIPS (Million Instructions Per Second)

Special-Purpose Systems

Real-Time OS
- Keep deadline: guarantee response time for critical tasks
- Soft real-time: best-effort to meet deadlines -- priority (e.g. multimedia)
- Hard real-time: must meet deadlines (no/limited secondary storage) (e.g. nuclear power plant)
Multimedia Systems
- a wide range of app: audio, video ...
- timing constraints: 24~30 fps
- on-demand/live streaming: played but not stored
- compression/decompression
Handheld/Embedded Systems
- specialized OS for small devices
- constraints: limited memory, low power consumption, small display, simple I/O