1. CSIS-110 Introduction to Computer Science
Dr. Meg Fryling
“Dr. Meg”
Fall 2012
@SienaDrMeg
#csis110

2. Lecture Fourteen Agenda
Questions?
Exam questions?
Assignments
CSI Ch 6: Hardware
Homework 3 – Part I (1-3)
Note: Exam 1 Solutions on Piazza
If you don’t know why you got something wrong, please find out!

3. Assignments Readings: See course scheduled on syllabus Homework 3
The textbook readings are going to help you with homeworks AND labs
See pdf on Piazza
Homework 3
Due at START of class Monday 10/29
Program Template
Coming to class late does NOT extend your due date/time
Lab 5
Due at START of lab 6
Coming to lab late does NOT extend your due date/time

4. For Wednesday’s Class Install Racket on your laptop
Scheme programming environment
Bring your laptop to class
We will do some Scheme and Python programming in class

5. Memory – Volatile Registers Cache RAM Small storage in ALU
Contain one word (how big is that?) and info that will be needed immediately
Access is fast!
Cache
Small and fast
Usually built into processor chip
Processors can access without FSB
Contains copies of frequently used data
RAM
Main memory
Access via FSB if not found in Cache
Can be accessed directly (Random)
Word is usually 2 bytes (16 bits)
Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory.

6. Figure 6.1 The von Neumann architecture
Bus - A set of wires that connect all major sections
Figure 6.2 Data flow through a von Neumann architecture

7. The Fetch-Execute Cycle
Figure 6.3 The Fetch-Execute Cycle

8. Secondary Storage Devices
Why is it necessary to have secondary storage devices?
Can you name some of these devices?

9. Magnetic Disk Structure

10. Time to read/write data to disk
Address of data: Surface, track, sector
Seek time: Time it takes for the read/write head to get positioned over the right track
Latency: Time it takes for the sector to spin to the read/write head
Transfer Time: Time for one sector to move under the read/write head
Access Time: Time it takes for a block to start being read
Seek Time + Latency + Transfer Time

11. Disk Performance: Example
Rotation speed: rev. / min
Arm movement speed: 0.02 ms to move to the next track
Tracks per surface: 1000
Number of surfaces: 1
Sectors per track: 50
Characters (bytes) per sector: 512

12. Disk Example (cont’d)
First, convert the Rotation speed to Rotation time, in milliseconds (ms):
Step 1: convert rev/minute to rev/second:
7200 rev / 1 minute = 120 rev / second
Step 2: convert revolutions to seconds:
120 rev / 1 sec = 1 revolution in 1/120 of a second
Step 3: convert to decimal:
1/120 = seconds / revolution
Step 4: convert to milliseconds:
seconds/rev = 8.33 ms/ rev
7200 rev / 1 minute = 120 rev / second
120 rev / 1 sec = 1 revolution in 1/120 of a second
1/120 = seconds / revolution
seconds/rev = 8.33 ms/ rev

13. Disk Example (cont’d) Voila! Each rotation takes 8.33 ms!
Now we can use this to calculate …
seek time,
latency,
transfer time,
and total access time
7200 rev / 1 minute = 120 rev / second
120 rev / 1 sec = 1 revolution in 1/120 of a second
1/120 = seconds / revolution
seconds/rev = 8.33 ms/ rev

14. Time needed to move from the first to the last track
Best-case
Worst-case
Average-case
Seek Time
Time needed to move from the first to the last track
Time needed to move over 1/3 of the tracks
Latency
Time needed for one full revolution of the disk
Time needed for half of the revolution of the disk
Transfer Time
Time needed for a block to pass under the head
Total Access Time
Sum of the above
*We assume that in the average case, the read/right head moves about 1/3 of the total number of tracks.

15. Disk Example 1 (Continued)
Rotation speed: rev/ min
Remember we already calculated Rotation Time: 8.33 ms!
Arm movement speed: 0.02 ms to move to the next track
Tracks per surface: 1000
Number of surfaces: 1
Sectors per track: 50
Characters (bytes) per sector: 512
How many characters can be stored on a single disk?
Seek time
Latency
Transfer time
Total
Best
Worst
Average