1.1 Flashcards
(16 cards)
1.1.3
1. What is primary storage?
2. What is secondary storage?
3. What is virtual storage?
- Primary storage: memory, which is made up of RAM (volatile) and ROM. It is directly accessible by the CPU.
- Secondary storage: storage that is non-volatile. It is not directly accessible by the CPU.
- Virtual storage: storage that appears to be local but is physically located elsewhere.
1.1.3
1. What is optical media?
2. What are the advantages and disadvantages?
- Optical media: can be used to store songs, videos and multimedia files. Data is stored on pits and lands, generally circulating outwards from the centre.
- Advantage: easy to transport; suitable for distributing software, music, or movies. Disadvantage: less storage capacity compared to other types. Must have an appropriate reader.
1.1.3
1. What is magnetic media?
2. What are the advantages and disadvantages?
- Magnetic: multiple disk platters with a read/ write head.
- Advantage: is cheap and has a vast storage capacity. Disadvantage: has lots of mechanical moving parts, durability is an issue. Consists of two surfaces, each of which contains concentric circles (tracks) with each track divided into sectors.
1.1.3
1. What is solid state media?
2. What are the advantages and disadvantages?
- Solid state: Uses non volatile flash memory to store information. Uses: personal handheld devices, tables, smartphones, military all terrain laptops.
- Advantages: highly durable, very fast read/ write speeds, no noise, no mechanical moving parts, lower power consumption.
Disadvantages: Higher cost per gigabyte; flash memory cells can wear out after a certain number of write cycles.
What are the common features that both RAM and ROM contain?
- Both primary storage/main memory
- Both allow random access
- Both can store programs
- Connected to CPU via buses
What are the features that RAM contain?
Properties of RAM
access memory
Used to store programs and data currently in use
Write speed considerably faster than ROM write speed (large number of write cycles)
Faster to access than secondary storage
Nowadays, faster to read than ROM
Volatile
What are the features that ROM contain?
Properties of ROM
Read Only Memory
Small Capacity
Data stored in ROM can only be modified slowly, with difficulty, or not at all
Non volatile (persistent)
Used to store BIOS (firmware)
Embedded OS likely to be stored in ROM
- Why is RAM called random access?
- Describe the process that occurs when RAM is running low
- RAM is called “random access” because any storage location can be accessed directly.
- An area of secondary storage used by the OS as RAM. The operating system’s memory manager uses secondary storage such as the hard disk or flash drives as RAM. Pages/segments that have not been used recently are moved out of RAM to virtual memory. In the example above, if the user wanted to use program F (currently not in RAM), existing page(s) which are not being used are moved from physical RAM to virtual memory to make space.
- State one item that needs to be stored in RAM and give a reason why RAM is used
- What software items are stored in ROM and why is ROM necessary?
- Explain how paging and segmentation make more efficient use of memory.
- -User files/software/OS currently in use
-User must be able to alter contents of file/computer needs access to
software but needs to be able to replace it
- RAM offers direct access.
- RAM operates at a much faster speed than most secondary storage devices - -Boot file/program/BIOS
-Must be available when computer switched on (therefore must b stored on medium which is non-volatile)
- The boot program/BIOS must not be deleted/unintentionally
amended (and therefore is best stored on a read-only medium.) - Allow programs to be stored in non contiguous memory locations - new programs can fit around existing programs in RAM. Allows pages to be transferred to and from secondary storage (i.e. virtual memory).
Explain in depth how paging works
Paging is when memory is split up into equal sized sections known as pages. These can then be swapped between main memory and the hard disk as needed.
Data can be held in non-contiguous memory locations, making it easier to make the best use oof the remaining storage, and avoid having to move content around to fit in new programs. It allows pages to be transferred to and from secondary storage. As it is random access there is no performance drop vs sequential storage.
What are the four modes of memory addressing?
Four options:
• Immediate Addressing (literal)
• Direct Addressing (reference to a cell in memory)
• Indirect Addressing (reference to a cell in memory pointing to another cell)
• Indexed Addressing (reference plus offset)
Many processors will allow multiple addressing modes. When this is the case, a specific field is often set aside in the instruction to specify the addressing mode.
Explain immediate addressing (literal)
• Operand is an actual value, i.e. a literal number, rather than a memory
location. Literal.
• Needs no access to RAM - no fetch is required.
• Range of values is limited by the size of the operand (eg if there are 4 bits for the operand, the literal value can only be 0 - 15)
Explain direct addressing (pointer)
Operand is a memory location, like Little Man Computer.
This mode is good when programmer a wants global variable.
Address is constant throughout the program executive since it’s part of the assembly program instruction.
Explain indirect addressing (pointer to pointer)
Operand is a memory location pointing to
another memory location to be used.
Multiple fetches are required. This mode allows access to more memory.
Why? An 8 bit instruction might have 4 bits
for the opcode, 4 bits for the operand (max
16 memory locations can be referenced).
The pointed to memory location can use all 8
bits to reference 128 memory locations
available.
With code, we can compute indirect memory
addresses and change their values e.g. from
97 to 73 as shown right. This is really useful.
Without it, things like linked lists (year 2)
would be impossible.
Explain indexed addressing (pointer plus offset)
Operand is a memory location plus
an offset stored in a special Index
Register.
This mode is ideal to store and access values stored sequentially for example in arrays since arrays are stored in contiguous memory
locations. The pointer points to the memory location of the first element in the array. By
incrementing or decrementing the offset, different elements of the array can be indexed
Explain how segmentation works
Segmentation is the splitting up of memory into logical sized divisions, known as segments, which vary in size, They represent the structure and logical flow of the program.
