1. Computer Science 210 Computer Organization
Introduction to Computer Organization
Text Figures: COPYRIGHT 1998 MORGAN KAUFMANN PUBLISHERS, INC. ALL RIGHTS RESERVED

2. Computer Components
The abstract view of a computer is commonly divided into five basic components

3. High Level  Low Level

4. Memory
Stores: Numbers, text, programs, addresses, graphics, sound, video, etc. that are currently in use.
Divided into fixed size cells (fixed number of bits).
This size is commonly 8 bits, and this 8-bit unit is called a byte.

5. Memory Addresses Each cell has an address, an unsigned integer.
Address Cell Content
Each cell has an address, an unsigned integer.
All accesses to memory are via a specific address 1 2 3

6. Basic Memory Operations
Memory Fetch
Given a specific memory address.
Retrieve the content stored at that address.
Memory Store
Given a specific memory address and
a specific value,
store the given value in the cell with the specified address.

7. Memory Facts and Terminology
A cell is the minimum unit of access.
Access time is same for all cells - Random Access Memory or RAM (nanoseconds - billionths of second)
ROM - Read only Memory (fetch but not store)
Some data items require more than one cell. For example, an instruction might need four cells.

8. More on Memory
All addresses are of some fixed number of bits, say N. Addresses would be 0000…0  …1  Total of 2N cells … 1111…1  2N - 1

9. Terminology Storage capacity: Speed K  210 = 1024  Kilo as in Kb
M  220 = 1,048,576  Mega as in Mb
G  230 = 1,073,741,824 Giga as in Gb
Speed
1  = 1 microsecond = 1 millionth of second
1 ms = 1 millisecond = 1 thousandth of second
1 ns = 1 nanosecond = 1 billionth of second

10. Magnetic disks Magnetization used to store bits Capacity
floppy Mb
large disk packs - hundreds of Gb
Single-sided disk
Double-sided disk
Disk packs

11. Magnetic disks - cont.
Information stored on concentric circles called tracks. Hundreds or thousands of these, each holding up to 150Kb.
On disk pack, tracks at same diameter form a cylinder
Rotate on spindle at 3600 to 7200 rpm.
100,000 times slower than main memory.
50 times less expensive than main memory.

12. Cylinder and read/write heads

13. Sectors Sectors are hard-coded on disk and can not be changed.
Blocks are set by OS during formatting.
Interblock gaps have special codes.
Sector

14. Hardware address of a block
Block Address
Surface number
Track number within the surface
Block number
Reading and writing from/to a block is done from/to a buffer in main memory.
Data may be transferred in clusters of contiguous blocks.
Usually controlled by disk controller.

15. Time to read or write a block
Seek time: The time to position the head at the correct track. (12 to 14 ms on desktop)
Latency: Time for block to rotate under the head.
Block transfer time: Time to transfer the block.
Total: ms.