Category Archives: 1. Computer Systems

1. Computer Systems, Homework, Revision

Quick teaser

I lifed this from the 2011 paper it’s question 13

(b) The computer has a maximum addressable memory of 16 Gigabytes. Its address bus width is 32.
(i) Calculate the width of the data bus.
(ii) State why computers do not come with the maximum addressable memory installed.
(iii) State the effect that adding one new line to the address bus would have on the maximum addressable memory.

I thought it was a very good question. I will post the solution to it tomorrow, feel free to comment with your answer but I don’t want you to copy and paste it from the Marking Instructions above.

1. Computer Systems, Computing Higher

Computer Systems – Peripherals (arrangements)

During booklet four we will be looking at the following.

  • Description of the use and advantages of buffers and spooling
  • Description of a suitable selection of hardware, including peripherals, to support typical tasks including
    • production of a multimedia catalogue
    • setting up a LAN in a school
    • development of a school website
  • Justification of the hardware selected in terms of appropriate characteristics including
    • resolution
    • capacity
    • speed
    • cost
    • compatibility
  • Description of the features, uses and advantages of solid state storage devices including flash cards
  • Description of the development trends in backing storage devices
  • Description of the following functions of an interface:
    • buffering
    • data format conversion (serial to parallel and analogue to digital)
    • voltage conversion
    • protocol conversion
    • handling of status signals
  • Distinction between parallel and serial interfaces
  • Description and explanation of the current trends towards increasing interface speeds and wireless communication between peripherals and CPU
1. Computer Systems, Computing Higher

Factors that effect Computer Performance.

Lots of things effect computer performance. We were looking at a few of them in today’s lesson.

Different types of RAM can have a big impact on the performance of a computer system. Why? Data has to be moved in and out of RAM, the quicker this data can be accessed and moved the faster the processor can get to processing it. Cache improves performance, this high speed SRAM is located close (often in) the processor. It allows the contents of RAM to be stored close to the processor, the processor check here for the next instruction, if its not found then it checks RAM. Although this sounds a bit haphazard, cache can improve the performance of the machine quite significantly.

Then we recapped how RAM effects performance.

  • More RAM means less need to use virtual RAM, therefor an increase in speed.
  • Cache allows for faster access then when the processor gets a cache hits the contents are transferred quicker. there are different types of cache.
  • Increases in RAM speed has failed to keep up with the increase in RAM capacity but different RAM has different clock speeds and even different ways of access.

We went on to look at how the speed and type of a peripheral can effect performance and that they require an interface. The interface allows the CPU to talk to the peripheral. (some brief notes below but we will look at this in more detail in a future post)

Functions of an Interface

  • Buffering – holding data temporarily while in transit between the CPU and peripheral.
  • Data Conversion – changing data into a form the CPU can understand and vice-versa – protocol conversion e.g.
    • serial to parallel
    • voltage conversion
  • Handling Status Information – to show whether the device is ready to receive or send data e.g. is the printer ready or out of paper.

A big thank you to Mr. Allen in Airdrie Academy for letting me cut up and publish his revision notes – AA Computer Performance

1. Computer Systems, Computing Higher

Computer Performance Introduction

This topic is all about computer performance and the things that effect it. It is easy to say that  you know how things like, RAM, CPU, GPU, etc effect the performance of a computer. But WHY do they effect the performance?

Here is the section from the arrangement documents that cover this booklet.

  • Description and evaluation of the following measures  of performance: clock speed, MIPS, FLOPS, and application based tests
  • Description of the effect the following factors have on system performance: data bus width, use of cache memory, rate of data transfer to and from peripherals
  • Description of current trends in computer hardware, including increasing clock speeds, increasing memory and backing storage capacity

Today was all about benchmarks. We established early on in the lesson that clock speed was not a good way of comparing computing performance. A computer with a 3GHz CPU may not be as fast a 2GHz, why? well the 2GHz CPU may be a multicore processor or the computer may have faster RAM, more cache etc.

  • The first benchmark we looked at was MIPS , however different instructions require different numbers of clock cycles and there is no standard for measuring MIPS.
  • Floating Point Operations Per Second (FLOPS), this is a better measure of performance as floating point multiplications are basically the same for each processor.
  • Application benchmarks, these vary from application to application. It may be for example, how long does it take a package to render a special effect on a photograph. For games  machines we often quote Frames Per Second (FPS) benchmarks. A modern game is set to a pre-set graphic mode and the number of frames rendered per second is then recorded, example. Specialist benchmarking software can also be used to test the whole system, this is the software demoed in class.

Here is the list of the Top 500 computers in the world. Did you notice that the comparison was Petaflops?

1. Computer Systems, Computing Higher

Buses and Addressability

Today’s lesson was more a revision of topics that went before. However, we did learn a few important things.

  • To get the processors attention peripherals can make use of
    • Polling its a little like the teacher not letting anyone talk and asking everyone in turn if they need help
    • Interrupts this is like someone putting up their hand and the teacher stopping to deal with their problem before continuing.
  • The word size of the computer is the number of bits that can be manipulated as a single unit by the processor.
    • An ideal computer has a data bus that is the same size as its memory locations
  • The address bus determines the number of memory locations, however the data bus determines the size of each location. So to work out the amount of addressable memory, we must multiply the number of addresses by their size.
    • Total Addressable Memory = (2^address bus width) * Data bus width
    • IE a machine with a 16 bit Data Bus and 32 bit address bus would have
    • (2^32)*16 bits of accessible storage
    • or 8GB – Do the math yourself to prove it.
1. Computer Systems, Computing Higher, Homework

Homework for 14th Dec

  1. State the purpose of registers in a microprocessor. (1)
  2. Describe the purpose of two signals found on the control bus. (2)
  3. An IT manager believes that a Pegasus computer with a 700MHz processor is faster than a Hercules computer with a 650MHz processor. Suggest two reasons why he may be incorrect. (2)
  4. What is the purpose of a control unit in a CPU? (1)
  5. If a processor needs an instruction from memory, a read operation is carried out. Describe the steps of the memory read operation with reference to the processor, memory and buses. (4)
  6. Processor clock speed is one factor which affects system performance. Name one other factor and describe how it affects system performance. (2)
  7. Calculate the maximum amount of addressable memory that a processor with 24-bit address bus and 16-bit data bus could access. Express your answer in the appropriate units, (3)

Out of 15 – Some of the questions may be difficult but we did touch on them in class and will cover them fully on Wednesday. Blame the wind.