Category Archives: 6. External Sites

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?

Computing Higher

Answers for Homework for the 14th Dec

2 Comments
  • State the purpose of registers in a microprocessor. (1)
    • Registers are temporary storage locations on the processor which can be used to store data or instructions required by the CPU.
  • Describe the purpose of two signals found on the control bus. (2)
    • Read – signals a memory read operation is to take place
    • Write – signals a memory write operation is to take place
    • Clock – synchronises the signals being passed in and out of the processor
    • Reset – clears all registers and busses of data
    • Interrupt – tells the processor to save current process, run interrupt process until completed, then resume its activities (can be ignored)
    • NMI – tells the processor to save current process, run interrupt process until completed, then resume its activities (cannot be ignored)
  • 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)
    • Hercules computer may:
    • have larger data bus (so can transfer more bits per clock cycle)
    • have more RAM so can store more programs in fast-access memory
  • What is the purpose of a control unit in a CPU? (1)
    • A control unit manages all the other parts of the processor and makes sure that the program instructions of the computer are carried out in the correct order
  • 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)
    1. Address to be read stored in MAR
    2. Contents of MAR transferred to Address bus
    3. Read control line activated
    4. Contents of memory at location from Address bus placed on Data bus
    5. Contents of Data bus transferred to MDR
  • Processor clock speed is one factor which affects system performance. Name one other factor and describe how it affects system performance. (2)
    • Data bus size – the larger the data bus the more bits that can be transferred in one clock cycle
    • RAM – more fast-access memory improves system performance as the processor does not need to use slow-access Virtual RAM
    • Graphics card with VRAM – takes away complex graphic calculations from processor, leaving it free to carry out other operations
  • 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)
    • Addressable memory (bits) =
    • data bus (bits) x 2 ^ address bus (bits)
    • 16 x 2^24 = 268435456 bits
    • /8 = 33554432 bytes
    • / 1024 = 32768 Kb
    • / 1024 = 32 Mb
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.

1. Computer Systems, Computing Higher

Cache Memory

Today’s lesson was a bit of a race, it covered Cache memory, SRAM & DRAM.

Its important that you remember that Cache Memory is not the same as Internet Cache. If you can’t get your head around how me running back and forth to the filing cabinet was caching then have a look here.

As a by the way, we also learned today that a memory location can hold more that one bit. I wonder if that will be useful in the future?

Computing Higher, Revision

Older Posts

Remember that the blog is now in its second year and some of the older posts may be very useful to you. A lot of them were written by pupils who were trying to understand the topic while they wrote it.

Browse back or use the search at the side.

There are currently 31 posts tagged with computer systems.