1 - Systems architecture

State the purpose of the CPU? [2]

The purpose of a computer is to take in data (1), process it (1) and then output (1)

What is hardware and software? [2]

- Hardware is the physical stuff that makes up your computer. - Software is the programs or applications that a computer system runs.

Define what is meant by an embedded system? [1]

Embedded systems are computers built into other devices.

Why are embedded systems better than general purpose systems? [3]

- easier to design - cheaper to produce - more efficient at doing their task.

What is the control unit and what does it do? [3]

1. Controls and monitors hardware 2. Controls input and output of data 3. Controls the flow of data within the CPU

State two types of operations carried out by the ALU. [2]

- mathematical calculations - logic operations

Identify four events that take place during the fetch-execute cycle. [4]

An instruction is fetched from memory The instruction is then decoded The decoded instruction is then executed so that the CPU performs continuously The process is repeated The program counter is incremented The instruction is transferred to the MDR The address of the instruction to be fetched is placed in the MAR

Identify three devices, other than a Satellite Navigation system, that contain embedded systems. [3]

Dishwasher, microwave oven, traffic light

The tablet computer uses cache memory. Explain the purpose of cache memory [3]

Cache memory is a special type of very fast memory (1 mark)which stores instructions or data (1 mark)that are either frequently used, have recently been used or are about to be used (1 mark)much faster as it does not need to be fetched directly from RAM (1 mark).

State the name of the internal component that is responsible for executing the programs on a computer and controlling other internal components... [1]

CPU

What is cache? [1]

Cache is very fast memory in the CPU - which is slower than the registers but faster than RAM.

One characteristic of an embedded system is that the software is typically embedded in ROM Give two other characteristics of embedded systems... [3]

-Embedded systems typically have a slower clock speed as they don't need to do very much processing[1] . making them cheaper [1] . Embedded systems use less power than normal computer systems as there task are simple [1]

Identify four registers and explain how they are used in the fetch-decode-execute cycle... [4]

- MAR - Holds the address of the location that the data needs to be read/ written from - MDR - Holds the data before it is stored in or after it is read from the memory (actual data) - Program Counter - Holds the address of the next instruction to be run - Accumulator - Stores the result of the last calculation performed by the ALU.

Other than registers identify three components of the CPU and explain their functions.[3]

- ALU - Performs calculations and logical operations - Control Unit - Decodes instructions and controls the flow of data - Cache - Temporarily holds data so it can be accessed faster than data memory

Dipesh is thinking of buying a tablet computer to replace his old desktop computer. Describe how the CPU and RAM work together to enable the tablet computer to operate. [3]

Instructions / programs(currently running) / data are stored in the RAM... these are fetched from the RAM by the CPU / Processor ... where the instructions are executed / instructions are processed / data is processed

Describe an action the CPU might carry out during its execute phase. [1]

- Use the Arithmetic Logic Unit (ALU) to calculate complicated mathematical functions. - Move data from one memory location to another. - Jump to different addresses in a program based on decisions that the CPU makes

Briefly describe what happens during the fetch, decode and execute stages [3]

Fetch: Instructions and data are fetched from main memory into the CPU (1 mark) Decode: The control unit checks that the instruction is valid and that it can be carried out by the CPU (1 mark) Execute: The decoded instruction is carried out (1 mark)

i) The program counter holds a particular value during the fetch decode execute cycle. State the nature of this value[1] ii) Give two possible reasons as to why this value might change. [2]

i) It holds the memory address of the next instructionii) It increments by 1 when an instruction is fetched (1 mark) It changes by a given amount when told to by a jump instruction (1 mark)

What is the role of the Program Counter in the fetch-execute cycle? [2]

- Stores the address of the next instrcution to be fetched from memory - Its contents are incremented

What is the role of the 'memory' in the Vonn Neumann model? [1]

The memory holds the program instructions and the program data.

Describe what happens when the instruction is 'fetched'? [3]

- Copy memory address from the program counter to the MAR - Copy the instruction stored in the MAR address to the MDR - Increment the program counter to point to the address of the next instruction, ready for the next cycle.

Describe what happens when the instruction is 'decoded'? [1]

The instruction in the MDR is decoded by the Control Unit - which then prepares for the next step.

Describe what happens when the instruction is 'executed'? [1]

The instruction is performed.

Explain why data is held temporarily in the accumulator, rather than simply accessing it from RAM. [1]

The Accumulator is much quicker to access than RAM, since it is inside the CPU itself.

"Explain what is meant by the term ""Von Neumann Architecture"" [2]"

A computer where both the data and software currently being used (1) are stored in computer memory (1)

Explain the purpose of a register within the CPU [3]

A register is a special type of memory within the CPU which can hold a very small amount of data. [1] The registers are used to hold the data temporarily while a software program is running in RAM. [1] The registers allow the CPU to access the data very quickly, even faster than using the cache. [1]

What is the typical size of a register and cache? [2]

register - 32bits or 64 bits cache - 32MB

A business computer has one CPU which has a clock speed of 1 GHz. (a) Explain the effect of changing the CPU to one which has a clock speed of 1.5 GHz [2]

Increasing the clock speed will result in programs running faster. This is because more instructions are being processed each second.

Explain what is meant by overclocking [2]

Overclocking is where the CPU clock is set to run faster than the speed at which it was designed to run (1 mark). This can make CPUs overheat, causing crashes or permanent damage to the system (1 mark)

Jordan's computer has been running slowly for a long time. Suggest three things that he could do to help improve the performance of his CPU. [3]

Increasing the clock speed by installing a CPU with a faster clock/ overclocking your current clock (1 mark)Installing a CPU with extra cores i.e. going from one core to dual core or from dual core to quad core (1 mark)Buying a CPU with a larger cache (1 mark)Installing additional RAM (1 mark)Installing a graphics card (1 mark)

Explain why upgrading from a dual core to a quad core system will usually improve performance [3]

Increasing the number of cores can speed up processing (1 mark) and/or enable multiple tasks (1 mark) to be run simultaneously (1 mark). With a dual core system two tasks can be processed simultaneously whereas upgrading to a quad core system will enable up to four tasks to be processed at the same time.(1 mark)

Explain why a computer with a dual core processor may not be twice as fast as a single core processor with the same clock speed. [2]

Additional cores may be redundant if the software is only written for a single core [1] or if the output of one operation is required to perform the second operation (sequential) [1] so they cannot be processed simultaneously[1].

Explain the effect of increasing the cache size of the CPU. [2]

The cache is a small, but extremely fast type of RAM, often located inside the CPU chip. [1] Having a larger cache will speed up processing time because the CPU can access data and instructions more quickly than they can from RAM. [1] Programs will run faster [1]

The CPU has a clock speed of 3.8 GHz. Describe what is meant by a clock speed of 3.8 GHz. [2]

The number of FDE cycles run per given time/second/ the frequency that the clock 'ticks' [1] 3.8 billion cycles/instructions ... [1] ...per second [1]

Explain one reason why the cache size affects the performance of the CPU. [2]

• data is transferred faster [1]... • ...which makes a CPU more efficient [1] • It is faster to transfer to and from cache [1]... • ...than transferring to and from RAM [1]

How does increasing RAM affect the performance of a computer? [2]

- The more RAM the more applications or more memory-intensive applications it can run smoothly, making it faster overall. - However if the computer already has plenty of RAM (no virtual memory is used) then increasing RAM may make no difference to performance.

Emilie has a word-processed document and word-processor application saved on a hard drive. (a) Emilie double clicks the document to open it. Describe what must happen before the CPU can process the document. [2]

The word-processor program needs to be copied / loaded into RAM[1] The word-processed document needs to be copied to RAM[1]

Give two uses for ROM? [2]

ROM (read-only memory) is non-volatile and stores the boot-up instructions (BIOS) for the computer [1], it also performs self-checks and sets up the computer. [1]

List three items typically held in the RAM when a computer is running. [3]

- data - files - programs currently in use

Is secondary storage faster than RAM? [1]

no

State two differences between RAM and ROM. [4]

- RAM is volatile - all data is lost when the power is turned off whereas ROM is non-volatile - data is permanently retained without power. - RAM can be written to, and read from whereas ROM can be read only, so cannot be written to.

Abeel had a power cut whilst working on a spreadsheet document. He said that he lost the entire document but could still open the spreadsheet program when the power came back on. Explain why this was the case for Abeel. [2]

The spreadsheet program was stored on the hard drive and copied to RAM / main memory while the program was in use.[1] The document was created and stored in RAM[ 1], and disappeared because it was never saved [1]. If the document had been saved, it would have been copied to the hard disk [1].

An increase in RAM capacity can improve the speed of your computer. Explain why an increase in ROM size would not have the same effect. [2]

ROM is only required to be as large as the start-up instructions inside it.[1] Any additional space will make no difference.[1] New files cannot be written into new space as it is read-only.[1]

A home computer has many programs open. 16 GB of RAM is available, but the programs that are currently open require more memory than this. Describe how virtual memory can solve this problem. [4]

Virtual memory is an area of secondary storage (such as a hard drive). It is set aside to be used as extension to RAM. If there is no room left in RAM, then a program or data will be moved to virtual memory to make space for another program or data. If when the program or data is needed again, it is swapped back into RAM.

What is memory? [1]

Is the component of the computer that holds data, programs and instructions that are currently in use.

What is the purpose of primary memory being built in side the computer? [2]

Data can be read from and written to primary memory extremely quickly. [1] This gives the processor fast access to the data and instructions that the primary memory holds. [1]

Explain why getting more RAM would be preferable to using virtual memory. [2]

Access to data already in RAM is much faster than having to swap other programs in and out of RAM before accessing them.[1] Constantly swapping programs and data between RAM and the hard disk (virtual memory) can cause disk thrashing[1] which takes time and decreases performance[1]. Reading data from a hard disk is much slower than from RAM.[1]

Why do computers have primary storage? [2]

Main memory or RAM (Random Access Memory) is required to temporarily store the programs, instructions and data the computer needs whilst it is in operation.[2] Primary memory is built inside the computer. [1]As a result, data can be read from and written to primary memory extremely quickly. [1]

Nina wants to transfer photos from a digital camera to an external secondary storage device. (a) Define what is meant by 'secondary storage'. [1]

• Long term/non-volatile storage of data/files • External storage of data

State four characteristics of secondary storage devices that Nina should consider when choosing a device. [4]

• Capacity/size • Speed • Portability • Durability • Reliability • Cost

What is meant when describing the 'reliability' of a storage device? Refers to whether the data will be saved as expected. [2]

● Data is not effected when saved. ● No changes to file formatting.

Most computer systems use at least one storage device. Explain one reason why a secondary storage device is needed in most computer systems. [2]

● To store the files / e.g. operating system ● Even when the system is switched off / which must be non-volatile.

Kerry has 5GB of files to transfer from her laptop at work to her new computer. She has been told to buy an external solid-state device to do this. (i) Give one example of a solid-state device. [1]

● USB memory stick // USB drive ● Memory card // SD card

What is one internal secondary storage device?

● Hard disk drive (HDD) ● Solid-state drive (SSD)

Fatima has a tablet computer. When she turns off the tablet, or restarts it, all data stored in RAM is lost. (a) Fatima is able to re-open her apps on the tablet when she turns it on again.Explain why her apps have not also been lost. [2]

The programs are stored in secondary storage [1] This means that any apps can be loaded from the secondary storage into RAM again (once the device has booted up)[1]

What are the advantages and problems associated with the use of flash memory? [4]

Advantages Flash is durable will not break if dropped or exposed to heat. Very reliable as no moving parts. Very compact but can store a lot of data in a small space. Very fast access time compared to a hard disk or a DVD. Low cost and reliable. Light weight so easily portable. Problems Can get lost easily. Can wear out over a long time period. More expensive than CD or DVD. The metal part that is inserted into the USB port can become bent or damaged.

Why do cameras use solid state storage? (4)

- Portable/ Lightweight --> device needs to be carried - Small physical size --> can fit into a small camera - Durable/ No moving parts --> Device will be moved around so no damage when dropped - Large capacity --> stores videos which have large file sizes - Fast access/ read/ write speeds - Efficient power consumption --> long lasting battery life

What are the advantages and disadvantages of Magnetic storage? [4]

Advantages ● Store large capacity● Reliable ● Cost-effective Disadvantages ● Slow to write to and read from memory.● All data has to be read before reading the data you want - sequential● Not very portable/ durable● Additional equipment needed to read data from tape.

What are the advantages and disadvantages of Optical storage? [4]

Advantages ● Cheap ● Can be used for portable devices● Generally smaller in size Disadvantages● low capacity● easily damaged - low durability● slow write speed● Poor reliability

What are the advantages and disadvantages of Solid State storage? [4]

Advantages ● Memory is non-volatile. ● fast read/ write speeds ● Stores larger amount of data. ● highly durable (shock-proof)Disadvantages ● More expensive than magnetic.

Which storage device should(a) A database server in a busy office use... [3]

Hard disk drives (HDD) [1] have very high capacity [1] and are relatively inexpensive compared to SSDs [1]. Fast, durable and reliable.[1] (Or, could justify SSD on grounds of speed, capacity, reliability.)

What storage device should an... (b) Event photographs sent by post to a company from a photographer use... [3]

(b) CD or DVD.[1] Very inexpensive, costing only a few pence [1], easy to post [1], and will only be used once [1].

What storage device should a... (c) Regular transfer of files between home and a place of work use... [3]

USB flash drive. [1] Has sufficient capacity and speed for this purpose [1], very portable [1], durable [1], reliable [1] and inexpensive [1]. (Accept valid alternatives.)

Describe what happens in the fetch decode execute cycle [6]

• An instruction is fetched from memory using the address in the program counter • The address of the instruction to be fetched is placed in the MAR • The instruction is transferred to the MDR • The program counter is incremented • The instruction is then decoded by the control unit. • The decoded instruction is then executed so that the CPU performs continuously • (Any additional data is fetched) • The process is repeated

what is the difference between storing data and an address? (2)

Data is coverted into binary form and stored on the computer's memory whereas the address is the term used to describe the location of an item of information.

What is the role of the MAR?

The MAR stores the memory location for the data that need to be fetched from the memory or stored into the memory.

What the role of the MDR?

The MDR stores the data that has been fetched from or is waiting to be sent to the memory.

Can the CPU access programs for secondary storage if not why? (2)

NO, the CPU cannot access a program directly from secondary storage - it needs to be loaded by the operating system into the primary storage/ main memory (RAM)