Introduction to Computer Organization and Architecture - Study Notes

1.1 Overview

Why study computer organization and architecture?
- Design better programs, including system software such as compilers, operating systems, and device drivers.
- Optimize program behavior.
- Evaluate (benchmark) computer system performance.
- Understand time, space, and price tradeoffs.

1.1 Overview (2/2)

Computer organization
- Encompasses all physical aspects of computer systems (e.g., circuit design, control signals, memory types).
- How does a computer work?
Computer architecture
- Logical aspects of system implementation as seen by the programmer (e.g., instruction sets, instruction formats, data types, addressing modes).
- How do I design a computer?

1.2 Computer Systems (1/2)

There is no clear distinction between matters related to computer organization and matters relevant to computer architecture.
Principle of Equivalence of Hardware and Software:
- Any task done by software can also be done using hardware, and any operation performed directly by hardware can be done using software.
- Assuming speed is not a concern.

1.2 Computer Systems (2/2)

At the most basic level, a computer is a device consisting of three pieces:
- A processor to interpret and execute programs
- A memory to store both data and programs
- A mechanism for transferring data to and from the outside world

1.3 An Example System (1/19)

Consider this advertisement:

1.3 An Example System (2/19)

Measures of capacity and speed:
- Kilo- (K) = 1 thousand = 10^3 and 2^{10}
- Mega- (M) = 1 million = 10^6 and 2^{20}
- Giga- (G) = 1 billion = 10^9 and 2^{30}
- Tera- (T) = 1 trillion = 10^{12} and 2^{40}
- Peta- (P) = 1 quadrillion = 10^{15} and 2^{50}
- Exa- (E) = 1 quintillion = 10^{18} and 2^{60}
- Zetta- (Z) = 1 sextillion = 10^{21} and 2^{70}
- Yotta- (Y) = 1 septillion = 10^{24} and 2^{80}
Whether a metric refers to a power of ten or a power of two typically depends upon what is being measured.

1.3 An Example System (3/19)

Hertz = clock cycles per second (frequency)
- 1 ext{ MHz} = 1{,}000{,}000 ext{ Hz}
- Processor speeds are measured in MHz or GHz.
Byte = a unit of storage
- 1 ext{KB} = 2^{10} = 1024 ext{ Bytes}
- 1 ext{MB} = 2^{20} = 1{,}048{,}576 ext{ Bytes}
- 1 ext{GB} = 2^{30} = 1{,}099{,}511{,}627{,}776 ext{ Bytes}
- Main memory (RAM) is measured in GB.
- Disk storage is measured in GB for small systems, TB (2^{40}) for large systems.

1.3 An Example System (4/19)

Measures of time and space:
- Milli- (m) = 1 thousandth = 10^{-3}
- Micro- (µ) = 1 millionth = 10^{-6}
- Nano- (n) = 1 billionth = 10^{-9}
- Pico- (p) = 1 trillionth = 10^{-12}
- Femto- (f) = 1 quadrillionth = 10^{-15}
- Atto- (a) = 1 quintillionth = 10^{-18}
- Zepto- (z) = 1 sextillionth = 10^{-21}
- yocto- (y) = 1 septillionth = 10^{-24}

1.3 An Example System (5/19)

Millisecond = 1 thousandth of a second
- Hard disk drive access times are often 10 to 20 milliseconds.
Nanosecond = 1 billionth of a second
- Main memory access times are often 50 to 70 nanoseconds.
Micron (micrometer) = 1 millionth of a meter
- Circuits on computer chips are measured in microns.

1.3 An Example System (6/19)

We note that cycle time is the reciprocal of clock frequency.
A bus operating at 133 MHz has a cycle time of 7.52 nanoseconds:
- 133{,}000{,}000 ext{ cycles/second} = 7.52 ext{ ns/cycle}

1.3 An Example System (7/19)

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1.3 An Example System (8/19)

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1.3 An Example System (9/19)

Computers with large main memory capacity can run larger programs with greater speed than computers having small memories.
RAM = random access memory; random access means memory contents can be accessed directly if you know its location.
Cache is a type of temporary memory that can be accessed faster than RAM.

1.3 An Example System (10/19)

3733 MHz 32 GB DDR4 SDRAM – This system has 32 GB of fast synchronous dynamic RAM (SDRAM)
128 KB L1 cache, 2 MB L2 cache – two levels of cache memory; L1 is smaller and probably faster than L2
Cache sizes are measured in KB and MB.

1.3 An Example System (11/19)

Dual storage (7200 RPM SATA 1 TB HDD, 128 GB SSD)
- Disk capacity determines the amount of data and size of programs you can store.
- The hard disk drive can store 1 TB. 7200 RPM is the rotational speed of the disk.
- Generally, faster disk rotation delivers data to RAM faster (many other factors involved).

1.3 An Example System (12/19)

Dual storage (7200 RPM SATA 1 TB HDD, 128 GB SSD)
SATA stands for Serial Advanced Technology Attachment; describes how the hard disk interfaces with other system components.
16x CD/DVD-RW drive
- A DVD can store about 4.7 GB of data.
- This drive supports rewritable DVDs (RW) that can be written to many times.
- 16x describes its speed.

1.3 An Example System (13/19)

10 USB ports, 1 serial port, 4 PCI expansion slots (1 PCI, 1 PCI-X 16, 2 PCI-X 1), HDMI
- Ports allow movement of data between a system and its external devices.
- This system has 10 USB ports, a serial port, and expansion slots.

1.3 An Example System (14/19)

Serial ports vs. parallel ports
- Serial ports send data as a series of pulses along one or two data lines.
- Parallel ports send data as a single pulse along at least eight data lines.
USB (Universal Serial Bus) is an intelligent serial interface that is self-configuring (plug and play).

1.3 An Example System (15/19)

System buses can be augmented by dedicated I/O buses.
PCI (Peripheral Component Interface) is one such bus.
1 GB PCIe video card; PCIe sound card
This system has two PCIe (PCI Express) devices: a video card and a sound card.

1.3 An Example System (16/19)

Active matrix technology uses one transistor per picture element (pixel).
Monitor resolution determines the amount of text and graphics displayable.
24" widescreen LCD monitor, 16:10 aspect ratio, 1920 x 1200 WUXGA, 300 cd/㎡, active matrix, 1000:1 (static), 8 ms, 24-bit color (16.7 million colors), VGA/DVI input, 2 USB ports
This monitor has a resolution of 1920 x 1200 pixels.
1 GB PCIe video card – The video card contains memory and programs that support the monitor.

1.3 An Example System (17/19)

Gigabit Ethernet – This system can connect to the Internet with speeds up to 1 Gigabit.

1.3 An Example System (18/19)

7-in-1 card reader – The card reader allows transfer from external media and has built-in Bluetooth.

1.3 An Example System (19/19)

Throughout the remainder of the book you will see how these components work and how they interact with software to make complete computer systems.
This statement raises two important questions:
- What assurance do we have that computer components will operate as we expect?
- What assurance do we have that computer components will operate together?

1.5 Historical Development

Moore’s Law (1965) – Gordon Moore, Intel founder – “The density of transistors in an integrated circuit will double every year.”
Contemporary version: – “The density of silicon chips doubles every 18 months.”
But this “law” cannot hold forever …

1.5 Historical Development (Rock’s Law)

Rock’s Law – Arthur Rock, Intel financier – “The cost of capital equipment to build semiconductors will double every 4 years.”
In 1968, a new chip plant cost about $12{,}000.
At the time, $12,000 would buy a nice home in the suburbs.
An executive earning $12,000 per year was “making a very comfortable living.”

1.5 Historical Development (Rock’s Law, continued)

In 2012, a chip plant under construction cost well over $5 billion.
$5 billion is more than the GDP of some small countries (e.g., Barbados, Mauritania, Rwanda).
For Moore’s Law to hold, Rock’s Law must fall, or vice versa. But no one can say which will give out first.

1.6 The Computer Level Hierarchy (1/7)

Computers consist of many things besides chips.
Before a computer can do anything worthwhile, it must also use software.
Writing complex programs requires a “divide and conquer” approach, where each program module solves a smaller problem.
Complex computer systems employ a similar technique through a series of virtual machine layers.

1.6 The Computer Level Hierarchy (2/7)

Each virtual machine layer is an abstraction of the level below it.
The machines at each level execute their own particular instructions, calling upon machines at lower levels to perform tasks as required.
Computer circuits ultimately carry out the work.

1.6 The Computer Level Hierarchy (3/7)

Level 6: The User Level – Program execution and user interface level – The level with which we are most familiar
Level 5: High-Level Language Level – The level with which we interact when we write programs in languages such as C, Pascal, Lisp, and Java.

1.6 The Computer Level Hierarchy (4/7)

Level 4: Assembly Language Level – Acts upon assembly language produced from Level 5, as well as instructions programmed directly at this level.
Level 3: System Software Level – Controls executing processes on the system. – Protects system resources. – Assembly language instructions often pass through Level 3 without modification.

1.6 The Computer Level Hierarchy (5/7)

Level 2: Machine Level – Also known as the Instruction Set Architecture (ISA) Level. – Consists of instructions that are particular to the architecture of the machine. – Programs written in machine language need no compilers, interpreters, or assemblers.

1.6 The Computer Level Hierarchy (6/7)

Level 1: Control Level – A control unit decodes and executes instructions and moves data through the system. – Control units can be microprogrammed or hardwired. – A microprogram is a program written in a low-level language that is implemented by the hardware. – Hardwired control units consist of hardware that directly executes machine instructions.

1.6 The Computer Level Hierarchy (7/7)

Level 0: Digital Logic Level – This level is where we find digital circuits (the chips).
Digital circuits consist of gates and wires.
These components implement the mathematical logic of all other levels.

1.7 Cloud Computing: Computing as a Service (1/6)

The ultimate aim of every computer system is to deliver functionality to its users.
Computer users typically do not care about terabytes of storage and gigahertz of processor speed.
Many companies outsource their data centers to third-party specialists, who agree to provide computing services for a fee.
These arrangements are managed through service-level agreements (SLAs).

1.7 Cloud Computing: Computing as a Service (2/6)

Rather than pay a third party to run a company-owned data center, another approach is to buy computing services from someone else’s data center and connect to it via the Internet.
This is the idea behind a collection of service models known as Cloud computing.
The “Cloud” is a visual metaphor traditionally used for the Internet. It is even more apt for service-defined computing.

1.7 Cloud Computing: Computing as a Service (3/6)

More Cloud computing models:
- Software as a Service, or SaaS. The consumer of this service buys application services.
- Well-known examples include Gmail, Dropbox, GoToMeeting, and Netflix.
- Platform as a Service, or PaaS. Provides server hardware, operating systems, database services, security components, and backup and recovery services.
- Well-known PaaS providers include Google App Engine and Microsoft Windows Azure Cloud Services.

1.7 Cloud Computing: Computing as a Service (4/6)

The general term, Cloud computing, consists of several models:
- Infrastructure as a Service (IaaS) provides only server hardware, secure network access to the servers, and backup and recovery services. The customer is responsible for all system software including the operating system and databases.
- Well-known IaaS platforms include Amazon EC2, Google Compute Engine, Microsoft Azure Services Platform, Rackspace, and HP Cloud.

1.7 Cloud Computing: Computing as a Service (5/6)

More Cloud computing models (cont.): – Cloud storage is a limited type of IaaS that includes services such as Dropbox, Google Drive, and Amazon.com’s Cloud Drive.

1.7 Cloud Computing: Computing as a Service (6/6)

Cloud computing relies on the concept of elasticity where resources can be added and removed as needed.
You pay for only what you use.
Virtualization is an enabler of elasticity:
- Instead of having a physical machine, you have a “logical” machine that may span several physical machines, or occupy only part of a single physical machine.
Potential issues:
- Privacy, security, having someone else in control of software and hardware you use

1.9 The von Neumann Model (1/8)

On the ENIAC, all programming was done at the digital logic level.
Programming the computer involved moving plugs and wires.
A different hardware configuration was needed to solve every unique problem type.
- Configuring the ENIAC to solve a “simple” problem required many days labor by skilled technicians.

1.9 The von Neumann Model (2/8)

Inventors of the ENIAC, John Mauchley and J. Presper Eckert, conceived of a computer that could store instructions in memory.
The invention of this idea has since been ascribed to a mathematician, John von Neumann, who was a contemporary of Mauchley and Eckert.
Stored-program computers have become known as von Neumann Architecture systems.

1.9 The von Neumann Model (3/8)

Today’s stored-program computers have the following characteristics:
- Three hardware systems:
- A central processing unit (CPU)
- A main memory system
- An I/O system
- The capacity to carry out sequential instruction processing.
- A single data path between the CPU and main memory.
- This single path is known as the von Neumann bottleneck.

1.9 The von Neumann Model (4/8)

This is a general depiction of a von Neumann system:
These computers employ a fetch-decode-execute cycle to run programs as follows . . .

1.9 The von Neumann Model (5/8)

The control unit fetches the next instruction from memory using the program counter to determine where the instruction is located.

1.9 The von Neumann Model (6/8)

The instruction is decoded into a language that the ALU can understand.

1.9 The von Neumann Model (7/8)

Any data operands required to execute the instruction are fetched from memory and placed into registers within the CPU.

1.9 The von Neumann Model (8/8)

The ALU executes the instruction and places results in registers or memory.

1.10 Non–von Neumann Models (1/2)

Conventional stored-program computers have undergone many incremental improvements over the years.
These improvements include adding specialized buses, floating-point units, and cache memories, to name only a few.
But enormous improvements in computational power require departure from the classic von Neumann architecture.
Adding processors is one approach.

1.10 Non–von Neumann Models (2/2)

Some of today’s systems have separate buses for data and instructions.
- Harvard architecture
Other non-von Neumann systems provide special-purpose processors to offload work from the main CPU.
More radical departures include dataflow computing, quantum computing, cellular automata, and parallel computing.

1.11 Parallel Computing (1/3)

In the late 1960s, high-performance computer systems were equipped with dual processors to increase computational throughput.
In the 1970s, supercomputer systems were introduced with 32 processors.
Supercomputers with 1,000 processors were built in the 1980s.
In 1999, IBM announced its Blue Gene system containing over 1 million processors.

1.11 Parallel Computing (2/3)

Parallel processing allows a computer to simultaneously work on subparts of a problem.
Multicore processors have two or more processor cores sharing a single die.
Each core has its own ALU and set of registers, but all processors share memory and other resources.
“Dual core” differs from “dual processor.”
- Dual-processor machines, for example, have two processors, but each processor plugs into the motherboard separately.

1.11 Parallel Computing (3/3)

Multi-core systems provide the ability to multitask (e.g., browse the Web while burning a CD).
Multithreaded applications spread mini-processes, threads, across one or more processors for increased throughput.
New programming languages are necessary to fully exploit multiprocessor power.

Conclusion

This chapter has given you an overview of the subject of computer architecture.
You should now be sufficiently familiar with general system structure to guide your studies throughout the remainder of this course.
Subsequent chapters will explore many of these topics in great detail.