1. Back of the Envelope Estimation

2. Principles Work does not compress A bad estimate is better than none.
Use Queuing Theory
Look at the resources

3. Quantities Time CPU seconds of processes and functions Code size
Instruction path lengths
Real time/Response time
Support time
Back up, batch audits, admin duties

4. Quantities (cont.) Memory Text, data, bss, stack, heap of a process
Shared memory
System resources
Message queues
Buffers
System tables

5. Quantities (cont.) I/O Bandwidth of channels
Number of concurrent I/O ops
Data Size
Disk speed

6. Quantities (cont.) Messages Quantity per unit time
Distribution over type, priority, time, etc.
Transit time in the system

7. Estimation