This document discusses synchronous and asynchronous computation in distributed systems. Synchronous distributed systems have bounded process execution times and message transmission delays, allowing them to be used for hard real-time applications through timeouts. However, they are difficult and costly to implement. Asynchronous distributed systems have no bounds on timing, making them unpredictable but able to tolerate unpredictable delays and crashes. Event ordering helps determine the sequence of events across processes.

1. PARALLEL AND DISTRIBUTED COMPUTING
SYNCHRONOUS/ASYNCHRONOUS COMPUTATION

2. SYNCHRONOUS
 Coordination of actions between processes
 Usually asynchronous i.e. process are independent
 but sometime we need to cooperate/synchronize for
 Mutual exclusion or for event ordering.
 Synchronization in distributed system is harder because clock
system of every system having own clock and no shared memory
(different)

3. COMPUTER CLOCK
 Each computer in distributed system has its own internal clock
and can result in different time read values hen two processes
running on different system.
 Clock synchronization is a mechanism to sync.The time of
all computers in distributed system.

4. SYNCHRONOUS DISTRIBUTED SYSTEM
 Process execution time lower and upper bound are set.This
time include transmission, transportation and receiving time of
messages
 This time is known to all involved processes.
 Drift rates between local clocks have known bound
 Transmitted messages are received within known bound time
 Can be used for hard real time applications
 Timeouts are used to detect failure
 Difficult and costly to implement

5. ASYNCHRONOUS DISTRIBUTED SYSTEM
 No Bound on process execution time, message transmission delay
and drift rates
 So, a distributed system is asynchronous if there is no bounds on
message delivery time, speed of involved processes and clock drift.
 Unpredictable in terms of timing
 No timeouts can be used.
 Process can crash or be too slow.

6. EVENT ORDERING
 Helps in knowing wheatear an event at one process occurred
before, after or concurrently with another event at another
process.