Cache memory is located between the processor and main memory. It is smaller and faster than main memory. There are two types of cache memory policies - write-back and write-through. Mapping is a technique that maps CPU-generated memory addresses to cache lines. There are three types of mapping - direct, associative, and set associative. Direct mapping maps each main memory block to a single cache line using the formula: cache line number = main memory block number % number of cache lines. This can cause conflict misses.
Το 3ο κεφ?λαιο στο μ?θημα Επικοινων?ε? Δ?κτυα & Τεχνολογ?α Η/Υ τη? Β’ Τ?ξη? ΕΠΑΛ του Τομ?α Ηλεκτρονικ??. Η παρουσ?αση αυτ? (μετατροπ? PPT σε PDF) ε?να? ενεργ? και συνοδε?εται απ? κ?ποια αρχε?α τα οπο?α συνδ?ονται με υπερσυνδ?σει?. Περισσ?τερε? πληροφορ?ε? στην σελ?δα :
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The document discusses arithmetic pipelines used in computers. It describes how pipelines divide sequential processes into sub-processes that execute concurrently. As an example, it explains the 4-part floating point addition and subtraction process, including comparing exponents, aligning mantissas, adding or subtracting mantissas, and producing the result. Registers are used to store intermediate results between operations. The document also briefly mentions that RISC pipelines typically have 2-3 segments - one to fetch instructions, one for ALU execution, and optionally one for storing results.
The document discusses interrupts for the 8085 microprocessor. There are two types of interrupts - maskable and non-maskable. Maskable interrupts can be delayed or rejected using EI and DI instructions, while non-maskable interrupts cannot be delayed or rejected. Interrupts can also be classified as vectored or non-vectored depending on whether the address of the service routine is hardcoded or needs to be supplied externally. The 8085 has specific interrupt inputs including INTR, RST 5.5, RST 6.5, RST 7.5, and TRAP. These interrupts differ in terms of whether they are maskable or vectored. Instructions like SIM and RIM can be used to manipulate
This document discusses real-time operating systems (RTOS). It defines an RTOS as a multitasking OS that meets time deadlines and functions in real-time constraints. The document outlines RTOS architecture, including the kernel that provides abstraction between software and hardware. It also discusses RTOS features like tasks, scheduling, timers, memory management, and inter-task communication methods. Examples of RTOS applications include medical devices, aircraft control systems, and automotive components.
Double Data Rate Synchronous Dynamic Random-Access Memory, officially abbreviated as DDR SDRAM, is a double data rate (DDR) synchronous dynamic random-access memory (SDRAM) class of memory integrated circuits used in computers. DDR SDRAM, also retroactively called DDR1 SDRAM, has been superseded by DDR2 SDRAM, DDR3 SDRAM, and DDR4 SDRAM, and soon will be superseded by DDR5 SDRAM. None of its successors are forward or backward compatible with DDR1 SDRAM, meaning DDR2, DDR3, DDR4 and DDR5 memory modules will not work in DDR1-equipped motherboards, and vice versa.
Compared to single data rate (SDR) SDRAM, the DDR SDRAM interface makes higher transfer rates possible by more strict control of the timing of the electrical data and clock signals. Implementations often have to use schemes such as phase-locked loops and self-calibration to reach the required timing accuracy.[4][5] The interface uses double pumping (transferring data on both the rising and falling edges of the clock signal) to double data bus bandwidth without a corresponding increase in clock frequency. One advantage of keeping the clock frequency down is that it reduces the signal integrity requirements on the circuit board connecting the memory to the controller. The name "double data rate" refers to the fact that a DDR SDRAM with a certain clock frequency achieves nearly twice the bandwidth of a SDR SDRAM running at the same clock frequency, due to this double pumping.
ARM processors handle exceptions and interrupts by mapping them to different processor modes and using an exception vector table to point to the corresponding handler addresses. The highest priority exceptions are reset, data abort, and FIQ. IRQ is the second highest interrupt. When an exception or interrupt occurs, the processor saves context by storing CPSR to SPSR and PC to LR, then loads the handler address and jumps to the exception mode. Handlers preserve context, service the request, then return using LR or stack to restore context and resume original execution mode.
This document discusses different types of flip-flops used in circuit design, including their diagrams and operating principles. It covers conventional CMOS flip-flops, resettable flip-flops, enabled flip-flops, and differential flip-flops. For each type, it provides details on their circuit implementation and how inputs like clock, reset and enable signals determine the output. The document also briefly outlines advantages like simpler circuit design, and disadvantages like reaction time between input-output changes.
The document discusses cache memory and provides information on various aspects of cache memory including:
- Introduction to cache memory including its purpose and levels.
- Cache structure and organization including cache row entries, cache blocks, and mapping techniques.
- Performance of cache memory including factors like cycle count and hit ratio.
- Cache coherence in multiprocessor systems and coherence protocols.
- Synchronization mechanisms used in multiprocessor systems for cache coherence.
- Paging techniques used in cache memory including address translation using page tables and TLBs.
- Replacement algorithms used to determine which cache blocks to replace when the cache is full.
1. The document discusses different types of registers, counters, and shift registers including their components, functions, and loading/shifting processes.
2. It also covers synchronous and asynchronous counters as well as ring and Johnson counters.
3. Finally, it discusses integrated circuits and different digital logic families including TTL, ECL, MOS, CMOS, and I2L.
The DDR PHY Interface (DFI) defines the signals, timing parameters, and programmable parameters required to transfer control information and data between the memory controller (MC), PHY, and DRAM devices. DFI allows MC and PHY IP cores developed by different companies to interoperate. It also provides a standardized interface for MC and PHY designs developed by different engineering groups within the same company. The DFI specification supports operating the PHY at higher frequencies than the MC, up to 4x, to enable higher DRAM frequencies and potential performance improvements for the system.
The document provides information about a signals and systems course taught by Mr. Koay Fong Thai. It includes announcements about course policies, assessments, and schedule. Students are advised to ask questions, work hard, and submit assignments on time. The use of phones and laptops in class is strictly prohibited. The course aims to introduce signals and systems analysis using various transforms. Topics include signals in the time domain, Fourier transforms, Laplace transforms, and z-transforms. Reference books and a lecture schedule are also provided.
The document discusses different instruction execution methods like straight-line sequencing and branching. It also covers addressing modes which specify how the location of an operand is represented in an instruction, including immediate, register, absolute/direct, indirect, indexed, relative, and auto-increment/decrement modes. Indexing allows accessing data in arrays by adding an index register or offset to a base register pointing to the array start. Relative addressing computes addresses as offsets from the program counter for branches.
The document describes the 8 addressing modes of the 8086 microprocessor. These are: 1) Immediate, where the operand is specified in the instruction itself. 2) Register, where operands are registers. 3) Direct memory, using a segment and offset address. 4) Register indirect, using a base register address. 5) Register relative, using a base register and displacement. 6) Base indexed, using a base and index register. 7) Relative indexed, using a base, index, and displacement. 8) Implied, where operands are implied and not specified.
The document describes the instruction set of the 8085 microprocessor. It discusses the different types of instructions such as data transfer, arithmetic, logical, branching, and control instructions. It provides details on specific instructions like MOV, MVI, ADD, SUB etc. and explains their operation, opcode, operands and purpose with examples. The 8085 has 246 instructions that are 8-bit binary values called opcodes. The data transfer instructions move data between registers and memory. Arithmetic instructions perform operations like addition, subtraction, increment and decrement.
The document discusses the flag register in processors like the 8086 and 8088. It explains that the flag register is a 16-bit register that contains status flags indicating the result of arithmetic operations like carry, zero, sign, overflow, and parity. It contains six status flags and three control flags that can be set or reset by programmers to control functions like interrupt handling and string instruction direction. The status flags provide information about the results of operations to determine subsequent instruction execution.
This document discusses different types of flip-flops used in circuit design, including their diagrams and operating principles. It covers conventional CMOS flip-flops, resettable flip-flops, enabled flip-flops, and differential flip-flops. For each type, it provides details on their circuit implementation and how inputs like clock, reset and enable signals determine the output. The document also briefly outlines advantages like simpler circuit design, and disadvantages like reaction time between input-output changes.
The document discusses cache memory and provides information on various aspects of cache memory including:
- Introduction to cache memory including its purpose and levels.
- Cache structure and organization including cache row entries, cache blocks, and mapping techniques.
- Performance of cache memory including factors like cycle count and hit ratio.
- Cache coherence in multiprocessor systems and coherence protocols.
- Synchronization mechanisms used in multiprocessor systems for cache coherence.
- Paging techniques used in cache memory including address translation using page tables and TLBs.
- Replacement algorithms used to determine which cache blocks to replace when the cache is full.
1. The document discusses different types of registers, counters, and shift registers including their components, functions, and loading/shifting processes.
2. It also covers synchronous and asynchronous counters as well as ring and Johnson counters.
3. Finally, it discusses integrated circuits and different digital logic families including TTL, ECL, MOS, CMOS, and I2L.
The DDR PHY Interface (DFI) defines the signals, timing parameters, and programmable parameters required to transfer control information and data between the memory controller (MC), PHY, and DRAM devices. DFI allows MC and PHY IP cores developed by different companies to interoperate. It also provides a standardized interface for MC and PHY designs developed by different engineering groups within the same company. The DFI specification supports operating the PHY at higher frequencies than the MC, up to 4x, to enable higher DRAM frequencies and potential performance improvements for the system.
The document provides information about a signals and systems course taught by Mr. Koay Fong Thai. It includes announcements about course policies, assessments, and schedule. Students are advised to ask questions, work hard, and submit assignments on time. The use of phones and laptops in class is strictly prohibited. The course aims to introduce signals and systems analysis using various transforms. Topics include signals in the time domain, Fourier transforms, Laplace transforms, and z-transforms. Reference books and a lecture schedule are also provided.
The document discusses different instruction execution methods like straight-line sequencing and branching. It also covers addressing modes which specify how the location of an operand is represented in an instruction, including immediate, register, absolute/direct, indirect, indexed, relative, and auto-increment/decrement modes. Indexing allows accessing data in arrays by adding an index register or offset to a base register pointing to the array start. Relative addressing computes addresses as offsets from the program counter for branches.
The document describes the 8 addressing modes of the 8086 microprocessor. These are: 1) Immediate, where the operand is specified in the instruction itself. 2) Register, where operands are registers. 3) Direct memory, using a segment and offset address. 4) Register indirect, using a base register address. 5) Register relative, using a base register and displacement. 6) Base indexed, using a base and index register. 7) Relative indexed, using a base, index, and displacement. 8) Implied, where operands are implied and not specified.
The document describes the instruction set of the 8085 microprocessor. It discusses the different types of instructions such as data transfer, arithmetic, logical, branching, and control instructions. It provides details on specific instructions like MOV, MVI, ADD, SUB etc. and explains their operation, opcode, operands and purpose with examples. The 8085 has 246 instructions that are 8-bit binary values called opcodes. The data transfer instructions move data between registers and memory. Arithmetic instructions perform operations like addition, subtraction, increment and decrement.
The document discusses the flag register in processors like the 8086 and 8088. It explains that the flag register is a 16-bit register that contains status flags indicating the result of arithmetic operations like carry, zero, sign, overflow, and parity. It contains six status flags and three control flags that can be set or reset by programmers to control functions like interrupt handling and string instruction direction. The status flags provide information about the results of operations to determine subsequent instruction execution.
This document summarizes Farhan Mashraqi's presentation about scaling the MySQL database that powers the photo blogging website Fotolog. It describes how Fotolog has grown to host over 228 million photos and 2.47 billion comments. The MySQL infrastructure consists of 32 servers split across four clusters to handle the large volume of reads and writes. Key aspects discussed include table partitioning, improving performance through index changes and switching to InnoDB, and strategies for ongoing scalability.
This document discusses Google's systems for handling large datasets, including their hardware infrastructure, distributed systems like GFS and BigTable, and future directions. It notes that Google uses many low-cost machines running Linux and in-house software to provide redundancy and scalability. Distributed file system GFS and database BigTable are used to store and access petabytes of data across thousands of machines.
25. 典型应用对系统资源使用的特点 声明 这部分内容主要是本人在网站工作多年的一些实践经验积累， 所以这些经验并不完全适用于其他的应用环境。 在我的经验中，大多数的硬件性能问题主要和 CPU 、磁盘、内存相关， 还没有遇到因为开发语言的运行效率对整个应用的性能造成影响，而应用程序设计的缺陷和数据库查询的滥用反倒是最最常见的性能问题。 需要注意的是，大多数情况下，虽然性能瓶颈的起因是程序性能差或者是内存不足或者是磁盘瓶颈等各种原因，但最终表现出的结果就是 CPU 耗尽，系统负载极高，响应迟缓，甚至暂时失去响应，因此我们观察服务器状况时，最先看的就是系统负载和 CPU 空闲度。
27. 典型应用对系统资源使用的特点 动态内容为主的 Web 应用 频繁执行程序，如 Perl, PHP, Java 等，消耗 CPU 严重 提供并发用户访问，因此系统进程数多，消耗内存多，当内存不足时，使用交换内存也会增加 CPU 的开销 磁盘的写 IO 比较频繁（主要为随机写），比如生成 cache 文件，更新 session 文件等。 内存充足时读取的内容可以被 cache 住， cache 的命中率和文件更新的频繁程度成反比，磁盘的读 IO 相对较小
28. 典型应用对系统资源使用的特点 静态内容为主的 Web 应用 ( 如 Squid Cache) 网络带宽瓶颈 小文件的随机读取频繁，内存充足时可以缓解磁盘随机读的压力 系统内存不足时磁盘 IO 量会比较大（读、写、交换内存），因此增加 CPU 的开销
29. 典型应用对系统资源使用的特点 数据库应用 数据库查询语句复杂，大量的 where 子句， order by, group by 排序等， CPU 容易出现瓶颈 表太大时，查询遍历全表造成磁盘读的 IO 量大，容易出现读 IO 等待的情况 数据更新量大或者更新频繁时，造成磁盘写的 IO 量大 内存不足时频繁使用交换内存
39. 工具介绍 -vmstat System in: 每秒产生的中断次数 cs: 每秒产生的上下文切换次数 上面这 2 个值越大，会看到由内核消耗的 CPU 时间会越多
40. 工具介绍 -vmstat Cpu us: 用户进程消耗的 CPU 时间百分比 us 的值比较高时，说明用户进程消耗的 CPU 时间多，但是如果长期超过 50% 的使用，那么我们就该考虑优化程序算法或者进行加速了 ( 比如 PHP/Perl) sy: 内核进程消耗的 CPU 时间百分比 sy 的值高时，说明系统内核消耗的 CPU 资源多，这并不是良性的表现，我们应该检查原因。 wa: IO 等待消耗的 CPU 时间百分比 wa 的值高时，说明 IO 等待比较严重，这可能是由于磁盘大量作随机访问造成，也有可能是磁盘的带宽出现瓶颈 ( 块操作 ) 。 id: CPU 处在空闲状态时间百分比
41. 工具介绍 -vmstat 情景分析 这个 vmstat 的输出那些信息值得关注？ Procs r: 运行的进程比较多，系统很繁忙 Io bo: 磁盘写的数据量稍大，如果是大文件的写， 10M 以内基本不用担心，如果是小文件写 2M 以内基本正常 Cpu us: 持续大于 50 ，服务高峰期可以接受 Cpu wa: 稍微有些高 Cpu id: 持续小于 50 ，服务高峰期可以接受
42. 工具介绍 -top 这个命令可以查看系统中运行的进程的状况， CPU 使用状况，系统负载，内存使用等。它是检查系统进程运行状况最方便的工具了，它默认显示部分活动的进程，并且按照进程使用 CPU 的多少排序。它可以显示全部 CPU 的使用状况，也可以显示每个进程都运行在那个 CPU 上面。 我习惯使用这个命令查看那些进程或者那类进程占用 CPU 和内存资源最多，以此迅速定位存在性能问题的进程，以及运行异常的进程。
47. 工具介绍 -top 用 top 看到的进程所处的几种状态 (STAT 列 ) 。 D 不可中断休眠，通常是 IO 操作所处的状态 R 正在执行的或者处在等待执行的进程队列中 S 休眠中 T 暂停刮起的（比如 Ctrl+Z ），也可能是被 strace 命令调用中的状态 Z 僵尸进程，进程执行完成，但由于其父进程没有销毁该进程，而被 init 进程接管进行销毁。 W 没有使用物理内存，所占用的物理内存被切换到交换内存 < 高优先级的进程 N 低优先级 有时候一个进程会有多个状态的标志，比如 SWN ， SW
48. 工具介绍 -top 情景分析 前面两次 top 的输出那些信息值得关注？ 图 1) Load average: 系统负载有降低的趋势，但仍然较高 Running: 有 3 个进程正在运行，正常，因为系统有 4 颗 CPU Cpu user: 接近 200% 了，有些大，服务高峰时可以接受 Cpu idle: 小于 200% 了，需要注意 图 2) Cpu iowait: 接近 200% 了，很大
63. 动态内容为主的网站 第二次优化 一段时间后，系统又开始不稳定，访问高峰时站点无法正常访问 分析系统资源使用状况，发现仍然是 CPU 耗尽后引起问题，但这次系统 IO 等待消耗的 CPU 资源比较大。 原因：上次解决了 CPU 资源容易耗尽的问题，目前网站访问量增加了， apache 进程数时常达到 256 个，导致内存使用殆尽，频繁使用交换内存，最终仍然导致 CPU 资源耗尽 处理：把 Apache 配置中的 KeepAlive 特性关闭，进程数大量减少，基本保持在 80 个进程以内，还是会使用交换内存，但是服务正常了。
64. 动态内容为主的网站 第三次优化 一段时间后，系统又开始不稳定，访问高峰时站点无法正常访问 分析发现还是 CPU 资源耗尽导致的原因。 原因：程序频繁访问数据库，大量的 SQL 语句中有 where, order by 等子句，而大量的表没有建索引，导致 MySQL 数据库负荷过高，消耗 CPU 资源过高。 处理：优化程序中的 SQL 语句， where 和 order by 子句上的字段建索引，程序增加 Cache 机制，再次使服务恢复正常。
73. 相关的参考资料 Red Hat Enterprise Linux Introduction to System Administration http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/admin-guide/ Sysstat 工具集 http://freshmeat.net/projects/sysstat/ 其他查看系统的 man 手册
