An OS can be seen as (1) a resource manager or (2) an extended machine.

Hardware: Processor (user vs privileged mode), memory, IO devices (network,
disk, and video), IO bus.

OS: Swapping.  Thrashing.  TLB.  Virtual memory (illusion of physical memory,
convenient mapping).  Page size.  Memory protection.

Kernel structure: Device drivers.  Userspace versus kernel mode.

Concurrency: Locks, semaphores, deadlock, livelock.  Race conditions.

Server: Events vs threads.  Stateful vs stateless.

Security: Authentication, access control.  Confidentiality vs privacy.
Cryptographic primitives: MACs, signatures (number theory vs one-time), hashes,
encryption (public and private).

Disks: Sector, track, cylinder, head, platter.  Sequential vs random access.  Properties of disks!  Seeks vs sequential read, failures, etc.

Definition of a transaction

TCP/IP basics.  Sockets programming.
  - Internet model (lowest common denominator, Internet goals -- interconnection, survivability) --> few assumptions about underlying network:  unreliable, datagram, etc.  (but deliver 99% of packets, minimum packet size, addressing.);
  - the network is an evil hostile place.  it will lose, mangle, delay, reorder your packets.
  - What UDP gets you (app demux; "ports", optional checksum)
  - What functions TCP fulfills (reliable, in-order bytestream)
  - Very rough model of TCP loss response:  cut throughput in half...

Definitions of delay in networks:
  propagation delay
  processing delay
  queueing delay

Bandwidth x roundtrip time = ideal amount of data in pipeline (avoid stalls)
High delay x bandwidth product => problems

Remote procedure calls.
 - External data representation (XDR/ntohl/htonl)
 - sunrpc