1.2 and 1.3 memory & 1.3 storage

1.2 and 1.3 memory & 1.3 storage

1. memory

   • rom
     • (Read Only Memory) is usually a flash memory chip on the motherboard that contains instructions needed to start up (boot) the operating system. ROM is non-volatile meaning that when power is removed, data is retained on the chip.
     • The ROM chip in a PC is usually called BIOS (Basic Input and Output System) There are other types of ROM chip too. BIOS is in ROM because it doesn’t need to be updated and will be retained even when power is turned off.
   • ram
     • (Random Access Memory) is a device that can plug into the motherboard. RAM contains programs, instructions and data that are currently being worked on (in use). RAM is volatile meaning that when the power is removed then all data is lost.
   • flash memory
     • refers to memory that is solid state (i.e. No moving parts) that retains data even when power is removed.
   • virtual memory
     • is for when the computer runs out of available RAM and so uses part of the HDD (Hard Disk Drive) instead. This is not desirable however, as the HDD is much slower than RAM and so makes the computer slower to respond. To use less Virtual Memory you could increase the amount of RAM you have. HOWEVER if your computer already has plenty of RAM to do what it needs, having more RAM may not make any difference to performance.
   • 1.2

2. storage

   • primary storage
     • (Sometimes called Main Memory) refers to the memory areas that the CPU can access very quickly (Cache, RAM and ROM). Primary storage has the fastest read/write speeds and is mostly volatile.
   • secondary storage
     • non-volatile – it’s where all data (operating systems, applications and user files) are stored when not in use (e.g. HDD, USB Flash drive, SD card). Read/write speeds are much slower compared to primary storage.
     • Characteristics when choosing secondary storage
       • Capacity – How much can it store?
         • Speed – What is the read/write speed?
           • Portability – Can you unplug/carry it around easily
             • Durability – How long is the product expected to function for before it is no longer useable
               • Reliability – How likely is it that the product will fail in its lifespan?
                 • Cost – How expensive is it
     • types of secondary stiorage
       • optical
         • CD (700MB), DVD(4.7GB), Blu-Ray(25GB)
         • (e.g. CD ROM, CD-RW, DVD ROM, Blu-ray) (USES LASERS TO READ DATA – how cool is that?!)
         • Cheap per GB and portable. Can even be given away on magazines!
         • Come in 3 forms (read-only (e.g. CD ROM), write once (e.g. CDR), re-writeable (e.g CDRW))
         • Use is declining (Netflix, Phones and tablets don’t have optical drives, cannot compete with USB flash drives)
         • Prone to getting scratched (not durable) and is slower than magnetic or solid state
       • magnetic
         • (e.g HDD, Floppy Disc, Cassette Tape, Magnetic tape)(Uses magnetisation of discs or tape to store data)
         • High capacity and reliable. HDDs are generally around 2TB at the moment
         • Portable versions of HDDs are useful for backing up and transporting large amounts of data
         • Sensitive to being dropped (i.e not durable)
       • solid state
         • (SSD (Solid State Drive), USB flash memory, SD card) (Uses NAND FLASH memory chips to store data)
         • No moving parts (only uses memory chips, no spinning motors that are noisy/generate heat)
         • Fast, reliable and highly portable (light and small). SSDs are generally around 128GB at the moment.
         • SD cards and USB Pen drives aren’t nearly as fast as SSDs, but still are very useful!
         • HDD
           • cheaper per GB than SSD
             • Generally higher capacity
         • SSD
           • Faster, silent & less heat / power needed
             • More shock proof/durable
   • So why doesn’t the CPU just go to the HDD to get data instead of going through RAM? - The reason that the CPU doesn’t access secondary storage directly is that it would make the hard drive work too hard and would be really slow (although this is how computers used to work a long time ago). It is far more efficient/quick for the CPU to request for a chunk of the HDD memory to be placed in RAM and for it to ‘feed’ off that so that the CPU isn’t waiting around too long.