Clustered Systems Overview

Interrupts

• The fixed location usually contains the starting address where the service routine for the interrupt is located.
• The interrupt service routine executes, and on completion, the CPU resumes the interrupted computation.
• Interrupts are an essential part of a computer architecture.
• Each computer design has its own interrupt mechanism, but several functions are standard.
• The interrupt must transfer control to the appropriate interrupt service routine.
• A table of pointers to interrupt routines can be used to provide the necessary speed.
• The interrupt routine is called indirectly through the table, with no intermediate routine needed.
• The table of pointers is stored in low memory, holding the addresses of the interrupt service routines for various devices.

Storage Structure

• Since RAM is volatile, it cannot be trusted to hold the bootstrap program.
• Electrically erasable programmable read-only memory (EEPROM) storage is used instead, which is infrequently written to and nonvolatile.
• All forms of memory provide an array of bytes, each with its own address.
• Interactions are achieved through a sequence of load or store instructions to specific memory addresses.
• The load instruction moves a byte or word from main memory to an internal register within the CPU.
• The store instruction moves the content of a register to main memory.

CPU Execution Cycle

• A typical instruction (execution cycle) as executed on a system with a von Neumann architecture:
  • Fetches an instruction from memory and stores it in the instruction register (CPU).
  • The instruction is then decoded and may cause operands to be fetched from memory and stored in an internal register.
  • If it is not in memory, then check and process for I/O interrupt.

Clustered Systems

• Clustered systems are composed of two or more individual systems—or nodes—joined together; each node is typically a multicore system.
• The generally accepted definition is that clustered computers share storage and are closely linked via a local-area network (LAN) or a faster interconnect.
• Clustering is usually used to provide high-availability service—that is, service that will continue even if one or more systems in the cluster fail.
• Each node can monitor one or more of the others (over the network).
• If the monitored machine fails, the monitoring machine can take ownership of its storage and restart the applications that were running on the failed machine.

Dual-Mode and Multimode Operation

• A properly designed operating system must ensure that an incorrect (or malicious) program cannot cause other programs—or the operating system itself—to execute incorrectly.
• The approach taken by most computer systems is to provide hardware support that allows differentiation among various modes of execution.
• At the very least, we need two separate modes of operation: user mode and kernel mode.

Memory Management

• The main memory is central to the operation of a modern computer system.
• Main memory is a large array of bytes, ranging in size from hundreds of thousands to billions.
• Each byte has its own address.
• Main memory is a repository of quickly accessible data shared by the CPU and I/O devices.
• The CPU reads instructions from main memory during the instruction-fetch cycle (van Neumann architecture).