00. Challenges of OS and disadvantages of Assembler language

Garry Shute's «Operating Systems → Virtualization of Resources» lecture

Operating system

Operating System

the discipline of unification, sharing and accounting of computer resources usage

Principal resources:

• Memory
• CPU
• Periferial devices

History:

0. Single user, single task — almost no OS needed, batch mode
1. Single user, many simultaneous tasks — accidental access prevention / sole resource locking, multitasking mode
2. Many users, many tasks — full access control, fair sharing, accounting, multitasking mode

Typical (monolith) architecture:

• Kernel: the implementation of the very mechanism (of unification, sharing and accounting) — API (application programming interface)
  • Memory: provisioning, protection, sharing
  • CPU: scheduling
  • Devices: access control
• Userspace: the logic above unification, sharing and accounting; common subtask solutions, high-level libraries, integration tools
• Applications: complete user workflow solutions (not a past of OS)

Much of kernel goals requires hardware implementation.

ABI (application binary interface) unification problem:

• Different architecture
• Different ISA (instruction set architecture) among similar architectures
• Different calling / register planning / other conventions
• OS specific: different kernel API (e. g. Linux-based, FreeBSD/MacOS, other *BSD, Windows, etc.)
  • ⇒ API/userspace standards:
    • POSIX
    • LSB
    • WinAPI

C programming language

Architecture-related unification cannot be developed over Assembler language due to it architecture-oriented nature ⇒ we need new cross-platform programming language, that, however, takes into account architecture features.

What is to be improved over assembler language:

• arithmetical expressions
• calling conventions
• execution flow primitives (conditionals and loops)
• variable strategies (static in memory / on stack memory / on registers)
• scalar types and address arithmetic
• complex data type modelling
• …

What is not to be changed:

• Actual memory/addressing model
• Actual hardware-provided scalar types (integers and floats)
• Bitness (machine word size) and endianness (byte order)

TODO

H/W

• Install and run MIPS virtual machine