CSE 2421
CSE 2421
Computer Systems
Required Reading: Computer Systems: A Programmer’s Perspective, 3rd Edition
Chapter 1, Sections 1.4 through 1.7.4, Section 1.9.3
Chapter 6 thru 6.1.3
Chapter 8, Section 8.2 through 8.2.4
What is a system?
“A collection of intertwined hardware and systems software that must cooperate in order to achieve the ultimate goal of running application programs”
Computer hardware
The hardware in a digital computer system must perform a number of basic operations:
Data storage: storing digital data in a form which balances
considerations of cost, reliability, and access speed.
Data movement: moving data from one system component to another, or within a given component.
3. Data transformation: changing a given bit pattern to a related one.
Computer Hardware Complexity
The current generation of CPUs have a much higher level of complexity than we are going to discuss in Systems I.
Current CPUs can actually execute several different instructions simultaneously, but we will not be looking at this.
The intent of Systems I is to give you a working understanding of the CPU and over system hardware architecture and how they fit together.
Data storage
Solid-state data storage uses state elements – latches or flip-flops
Two different kinds of logic elements:
a. Combinational – do not store state: current output depends only on current input.
b. Sequential (clocked) – capable of storing state: i.e., these elements have “memory” – they can remember or store a prior state.
Data movement
Data movement is done with buses – channels for transferring data from one system component to another (or within a component). The buses consist of “wires,” or conductive circuit traces (e.g., copper traces on a circuit board, or doped conductive silicon patterns in a processor, such as a CPU)
The system memory bus is divided into an address bus and a data bus, as well as some control lines (read line, write line, memory read complete line).
The CPU has two registers which it uses for memory accesses:
a. MAR (or Memory Address Register): to put an address on the address bus;
b. MDR (or Memory Data Register): to put data on the data bus, or to fetch data from the data bus.
CPU and Main Memory – 8 Byte Reads
When the CPU wants to read data from memory, it puts the address of the first byte to be read in the MAR, and sets the read line to 1.
The CPU always reads at least 8 bytes at a time.
When the memory unit detects that the read line is set to 1, it gets the address off of the address bus, gets the eight bytes at that address from memory, and puts them on the data bus, and sets the memory read complete line to 1.
The 8 bytes from the data bus are transferred to the MDR when the CPU detects that the memory read complete line is 1.
CPU and Main Memory – 8 Byte Writes
When the CPU wants to write data to memory, it puts the address of the first byte to be written in the MAR, puts the data to be written in MDR, and sets the write line to 1.
When the memory unit detects that the write line is set to 1, it gets the address off of the address bus, gets the eight bytes to be written from the data bus, and writes them to memory at the address it got from the address bus.
Data transformation
Data transformation, for example, in the CPU, is done with a combination of:
state elements, which store input(s) and output of the operation, plus
combinational circuits which actually perform the transformation (modify the appropriate bits in the input to produce the output).
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Hardware Organization (big picture)
PC
ALU
Bus Interface: MAR
MDR, control lines
I/O
bridge
Main
memory
Disk Controller
USB controller
Graphics adapter
Disk
Display
Keyboard
Expansion slots for other devices such as network adapters, video cards, etc.
Memory bus
System bus
Register File
I/O bus
Mouse
CPU
IR
Cache(s)
Control
USB – Universal Serial Bus
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Instruction Set Architecture
Instruction Set Architecture (ISA) – an abstraction which specifies
The processor state
The format of the instructions
The effect each instruction will have on the processor state
PC’s use x86 (mostly, X86-64 these days)
CPU components
Registers (not directly accessible by user programs):
Note: All registers described in the following slides are 64 bits (i.e. 8 bytes) in 64 bit processors, unless otherwise noted.
a. PC (Program Counter): This holds the address of the current instruction. It will be incremented to point to the next instruction as part of the execution of the current instruction.
b. IR (or Instruction Register): A register where the bits of the instruction are stored in order for the instruction to be executed. Before execution, the bytes in memory pointed to by the PC will be brought into the IR, and then the instruction is executed.
CPU components
Register File: Organized as an array of registers, with each register accessed by an index (i.e. uniquely named); X86-64 16 integer registers plus a completely different set for floating point numbers
ALU: Combinational logic to implement all of the Arithmetic and Logical Instructions which the CPU can perform; execution of these instructions sets some or all of the flags or condition codes. This computes new data and address values.
Control: Logic circuitry to control instruction fetching and execution.
EFLAGS register: A register in processors with one bit flags set by ALU instructions.
CPU components
MAR: A 64 bit register the CPU uses to put addresses for memory accesses on the address bus.
MDR: A 64 bit register which the CPU uses to put data on the data bus for writes, or to retrieve data from the data bus for reads from memory.
Motherboard or mainboard
(desktop system – server mainboards are similar)
Back panel input/output connectors
CPU package and pins
DIMM memory module
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Bus
Electrical conduit used to carry bytes of information between hardware components
Typically transfer fixed-size chunks known as a word
Size of a word depends on the “bitness” of the machine
32 bit systems (4 byte words typically)
64 bit systems (8 byte words typically)
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I/O Devices
Hardware devices connected to the outside world
Typical I/O devices
keyboard
mouse
display
disk drive
I/O devices are connected to the bus through either a controller or an adapter
Controller – chips that reside on the motherboard
Adapter – pluggable slot on the motherboard
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Main Memory
Temporary storage for applications which are being executed (i.e., instructions) and for data used by the applications
Organized as a linear array of bytes each with its own unique address starting at zero
Two types of memory technology (each with subtypes, which we will not look at)
SRAM (Static RAM)
DRAM (Dynamic RAM)
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SRAM
Static RAM
Each bit is implemented with a six transistor circuit
Each bit will retain its current value or state indefinitely as long as it has power
Resistant to electrical noise
Faster access time than DRAM (i.e., faster to read and write)
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DRAM
Dynamic RAM
Each bit is stored on a capacitor and 1 transistor
Retains value or state for only 10-100 milliseconds while power is applied
Modern CPU clocks tick in the nanosecond range
System will periodically refresh every bit by reading then rewriting it
Very susceptible to electrical noise
Slower access time than SRAM (i.e., slower to read and write)
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SRAM vs DRAM comparison
So what is each typically used for?
SRAM
CPU Cache (and other caches)
DRAM
Main memory
You might be able to tell SRAM from DRAM by the “S”. SRAM is “S”peedier than DRAM. Speedier memory will be closer to the CPU chip.
Transistors/bit Access Time Persistent State Electrically Sensitive Relative Cost
SRAM 6 1x yes no 100x
DRAM 1 10x no yes 1x
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Table from Computer Systems – Programmers Perspective
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Non-Volatile & Volatile Memory
Volatile memory will lose its information if the supply voltage is removed
Common volatile memory
RAM/caches
Non-Volatile memory will retain its data when powered off
Common Non-volatile memory
EEPROM (electrically erasable programmable read only memory)
Flash
Solid State Disks (SSD)
(Magnetic) Disk Drives
Tape drives
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Memory (Chapter 6)
The larger memory gets, the longer it takes to read from it
(and the less expensive it becomes)
Cache
Smaller and faster
Temporary staging areas
Make the transfer/copy operations happen asap. It’s easier and cheaper to make processors run faster than it is to make main memory run faster; thus, main memory is the system bottleneck (and the CPU-main memory speed gap has grown over time)
Memory Hierarchy
The storage at one level serves as a cache for storage at the next lower level
The farther you are away from the action, the longer it takes to make something happen
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Cache
Caching is the concept of having smaller faster devices act as a “staging area” for larger slower devices
Caching works because computer software exhibits the property of locality in memory access (see below).
The faster the memory, the more expensive it is to build, so there is a practical limit on how much fast memory we can put in the system, and still keep it affordable
Develop a caching strategy so that the fastest memory can be kept small
A memory system with effective caching can perform data access at an average speed close to that of the fastest storage, but have an effective size and cost per byte close to that of the largest storage device
The Memory Hierarchy
This refers to the concept of building a memory subsystem which consists of various levels of storage.
The storage at higher levels of the hierarchy has faster access times, but also has a smaller size (because it is also more expensive)
Conversely, the storage at lower levels of the hierarchy has slower access times, and has a larger size (because it is also less expensive)
The storage at a higher level acts as a cache for the storage at the level below it.
Data transfers from a lower level to a higher level are done in “chunks” or groups; that is, when data is transferred, a number of items of data (instructions or data values) are transferred.
The Memory Hierarchy cont.
This results in a memory subsystem with a larger effective size and lower cost (cost per byte close to that of the least expensive storage), but with faster average access speed (close to that of the fastest storage), because programs exhibit locality of memory access.
Two types of locality:
Spatial locality: If a particular piece of data (or instruction) is accessed by a program, other data/instructions at nearby locations in memory are likely to be accessed soon.
Temporal locality: If a particular piece of data (or instruction) is accessed by a program, the same piece of data or instruction is likely to be accessed in the near future.
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Caching and the Memory Hierarchy
http://faculty.etsu.edu/tarnoff/othr2150/mem_hier.gif
http://faculty.etsu.edu/tarnoff/othr2150/mem_hier.gif
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Why use tape??
Cheap
How often do you want to access it’s data?
Security. Really?
https://www.wsj.com/articles/companies-look-to-an-old-technology-to-protect-against-new-threats-1505700180
This link is from WSJ on 9/17/17.
https://wikibon.com/why-tape-is-poised-for-a-george-foreman-like-comeback/
This is from 6/24/14
Storage Vendors
HP Storage
Gone
IBM Storage
http://www-03.ibm.com/systems/storage
Dell Storage
http://www.dell.com/us/business/p/storage-products?~ck=anav
Oracle Storage
https://www.oracle.com/storage/index.html
IBM TS3500 Tape Library (at least 2 years old)
Highlights
Support highly-scalable, automated data retention on tape
Deliver extreme scalability and capacity
Provide up to 2.25 exabytes (EB) of automated, low-cost storage under a single library image
Enable data security and regulatory compliance via support for tape drive encryption and write-once-read-many (WORM) cartridges
Flexible library capacity with up to 192 drives in up to 16 TS3500 frames, and up to 15 libraries interconnected in a library complex
Simultaneous attachment of servers and applications to logical library partitions
Remote management with a web-based interface for library control and configuration
Oracle StorageTek SL8500Tape Library
(current)
http://www.oracle.com/us/products/servers-storage/storage/tape-storage/034341.pdf
How Big is a… ?
Bytes(8 Bits)
Kilobyte (1000 Bytes)
Megabyte (1 000 000 Bytes)
Gigabyte (1 000 000 000 Bytes)
Terabyte (1 000 000 000 000 Bytes)
10 Terabytes: The printed collection of the US Library of Congress
50 Terabytes: The contents of a large Mass Storage System
Petabyte (1 000 000 000 000 000 Bytes)
2 Petabytes: All US academic research libraries
200 Petabytes: All printed material OR Production of digital magnetic tape in 1995
Exabyte (1 000 000 000 000 000 000 Bytes)
5 Exabytes: All words ever spoken by human beings.
Zettabyte (1 000 000 000 000 000 000 000 Bytes)
From wikipedia:
Research from the University of California, San Diego reports that in 2008, Americans consumed 3.6 zettabytes of information.
Internet Traffic to Reach 1.3 Zettabytes by 2016
Yottabyte (1 000 000 000 000 000 000 000 000 Bytes) Named after Yoda.
*Xenottabyte (1 000 000 000 000 000 000 000 000 000 Bytes)
*Shilentnobyte (1 000 000 000 000 000 000 000 000 000 000 Bytes)
*Domegemegrottebyte (1 000 000 000 000 000 000 000 000 000 000 000 Bytes)
*These names may change
Amdahl’s Law (Section 1.9.1)
Basically says that when we speed up one part of the system, the overall effect on system performance depends upon how significant the part sped up is to the overall system and how big the speed improvement was
That is, to significantly speed up the entire system, the speed of a very large fraction of the overall system much be increased not just one piece
This law doesn’t just apply to computer systems, but any process or system that we’d like to improve. (e.g. manufacturing processes, cooking a meal, traveling cross country, etc.)
https://fastapasta.com/
Process Abstraction (Chapter 8)
This abstraction is provided by the OS
A process is a program in execution (every program is capable of being a process, but is not one until it is actually executing)
Allows a program to execute with the view that it is the only thing running (though it is virtually never the only thing running)
Application does not have to worry about sharing CPU time, or memory space (even though it virtually always actually is sharing those resources)
Each process in the system is managed by the OS using a process control block (PCB).
Process Abstraction
The PCB has information about the current state of the process (ready, running, blocked), and data that the OS uses to restore the process (PC and register values) to its previous state in order to resume the process after it goes from a blocked state (for input or output, for example) to a running state.
The process abstraction allows the CPU to be utilized more fully.
It increase throughput (the number of processes which can complete per unit time) at the cost of latency, or a delay in completion time for each process.
File abstraction (Chapter 1, Section 1.9.3)
Also provided by the OS
A file is just a collection of bytes sitting in some kind of storage.
Opening a file, or executing the program contained in an executable file, copies the bytes from disk into RAM.
The interpretation of the bytes (instructions, numerical data, characters, etc.) is determined by the software which is used to open the file.
Summary
A computer system is a mixture of hardware and systems software that cooperate to run application programs
Information in a computer is represented as groups of bits that are interpreted in different ways, depending upon the context.
Make a point to read Section 1.10 from the text
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