Explaining RAM

[Music] welcome to another video from explaining computers comm this time I'm going to talk about random access memory or RAM specifically I'm going to spend a few minutes talking about the nature and history of RAM before detailing those Ram technologies and form factors used in modern desktop and laptop computers computer storage can be volatile or non-volatile non-volatile storage includes hard drives and SSDs as these maintain their contents when power is disconnected in contrast modern RAM is volatile storage that loses its data when the power is switched off RAM is however the fastest kind of storage available and is used to hold programs and data when a computer is running ram kappa 30 is measured in gigabytes with one gigabyte being just over 1 billion bytes today 4 gigabytes is the minimum recommended ram through a modern Windows PC with 8 gigabytes or more required for most video editing and other high-end applications the first type of Ram to enter widespread use was magnetic core storage which featured tiny ferrite rings that were threaded on a lattice of wires bypassing voltages through the wires the Rings or cause could be magnetized with either a clockwise or anti-clockwise polarity so allowing the storage of one bit of data here you can see a magnetic core storage unit but I photographed at the National Museum of computing the unit has multiple planes of cause stacked one on top of the other with the uppermost core plane visible through the window on the top core storage was the most common form of RAM from the mid 1950s to the mid 1970s and was used in the Apollo spacecraft that took human beings to the moon in the early 1970s called storage started to be replaced with integrated circuit or ICU Ram early personal computers were subsequently fitted with many dual inline or dip RAM chips as we can see here such chips were usually plug directly into socket on the computer's motherboard which made RAM repairs and upgrades rather time-consuming even more significantly chip creep could occur with individual RAM chips having a tendency to rise out of their sockets due to constant thermal expansion and contraction to overcome these limitations Ram ship started to be soldered into packages on modules that were in turn plugged into a computers in both aboard to standard initially emerged known as sips and Sims as you can see a sip or single inline package had 30 pins that plugged into a row of tiny round sockets while great in theory sips could be tricky to fit were expensive to produce and it was easy to bend or otherwise damage their pins for this reason Sims or single inline memory modules became the dominant Ram technology like sips these were initially available with a 30 pin form factor although later Sims had 72 pins and sadly I don't have one of those available to show you here as you can see however sims have a robust edge connector and securely clip and lock into a motherboard Ram socket today's computers are fitted with descendants of sims known as dims or dual inline memory modules the key difference between a similar Tim is that the connections on either side of a sim or duplicated where was on a dim they are distinct and doubling the number of connection points in the same available space for optimum performance identical pairs of dims should be installed in two matching slots or banks on a computer's motherboard this allows the RAM to run in a so termed dual channel mode that maximizes the speed at which it can be accessed motherboard that can accommodate more than two dims almost always have their Ram slots color-coded to indicate appropriate insertion pairs as we'll see later in the video over the years dims have evolved to accommodate speed improvements it should also be noted that while all of the dims shown here offer use in a desktop PC smaller dims or small outline dual inline memory modules are used in laptops and other small computers for completeness I should also note but in the late 1990s and early noughties there was also another form of ram called the rim or Rambus inline memory module these were similar to dimmed but are no longer in use you rampe can be confusing because the specification of a modern dim is pretty extensive and may be expressed in many different ways for example the specification for the RAM module we have here could be listed like this clearly the 4gb at the front means that we have a 4 gigabyte component and as I've already explained the dim part on the end means that this is a dual inline memory module suitable for use in a desktop PC we can also see the RAM bit sitting there quite happily but with the letters s and D before it and to explain what this and the other terms here mean we need to delve a little deeper into RAM technologies the memory cells that store each bit of information in a Ram chip can be either static or dynamic in static RAM or SRAM each memory cell consists of four or more transistors that maintain data for as long as power is applied in contrast in dynamic RAM or DRAM each memory cell is built from a single transistor and a capacitor that requires a periodic power refresh because SRAM does not have to be constantly refreshed it is faster however SRAM is more expensive to manufacture than DRAM because more components are required to make up each memory cell because of this SRAM is used to provide micro processors and hard drives with some very fast internal storage called cache however most other computer RAM uses DRAM technology to provide the highest capacity of the lowest-cost specifically today personal computers are fitted with SDRAM memory modules SDRAM is a development of DRAM which stands for synchronous dynamic Ram what this means is that SDRAM operates in synchronization with a computer's clock cycle which reduces wait times for the processor and hence improves performance back in 2000 a development of SDRAM called DDR SDRAM was introduced DDR stands the double data rate and means that the RAM operates twice as quickly as two data transfers take place per clock cycle while than just one since it was introduced ddr sdram has been improved several times with subsequent generations called ddr2 ddr3 and ddr4 at the time of making this video in December 2018 a new standard for ddr 5 is awaited with ddr5 SDRAM likely to enter the market in 2019 or 2020 later generations of DDR SDRAM offer increasingly higher performance and have different physical form factors specifically at the top here we have a first generation full sized DDR SDRAM with 184 pins and below that a ddr2 module with 240 pins next there was a ddr3 SDRAM which also has 240 pins but which has a notch in a different location to prevent it from being inserted into a ddr2 socket finally we have a ddr4 SDRAM with 288 pins and again a different notch configuration note that the ddr3 and ddr4 modules here are supplied with an aluminium heat spreader to help cool their chips but that this is not always the case Ram modules in each DDR generation who are available in a range of speeds here for example we're looking at a table showing common speeds for different ddr3 SDRAM modules as you can see Ram speed can be expressed in several different ways with a data rate cited in mega transfers per second and an Associated peak transfer rate listed in megabytes per second as we can see the mega transfers per second figure may also be combined with a module DDR type while a pig transfer rate is often included within a module babel which is prefixed with PC and the DDR generation note but it's not uncommon for an SD roms data rate to be cited in megahertz even though mega transfers per second is more technically correct each generation of DDR SDRAM was developed to offer higher performance than the previous one and to illustrate this here is a table of common ddr4 modules which are clearly faster than the ddr3 modules we've just seen when at such data note with the peak transfer rate figure in megabytes per second is always eight times higher than the data transfer rate expressed in mega transfers per second note also that there are no definitive terms in use for the headings shown in these tables with variations on the wording used by different manufacturers and standards bodies I'm now very aware but I presented rather a lot of information and I could go on to detail even more RAM terminology however I think we've now had enough to make sense of a standard RAM module specification and so if we return to the component we had previously it's hopefully now clearer but its specification refers to a 4 gigabyte module based on fourth-generation double data rate synchronous dynamic Ram we can also see when the module operates with a data transfer rate of 2,400 mega transfers second equated to a pig transfer rate of 19200 megabytes a second and finally we also know that this Ram before us as a dual inline memory module form factor so what do you need to know when selecting RAM for a PC build or upgrade well without delving into even more technicalities the key things to note though its follows firstly desktop PCs require dims and laptops require sodium's secondly you need to fit the correct DDR generation for your motherboard as there's no backwards or forwards compatibility so for example you must fit ddr3 RAM into a ddr3 motherboard ddr4 ram into a ddr4 motherboard and so on thirdly you should fit Ram with a speed but is supported by your motherboard all motherboards accept several different modules speeds so make sure that the RAM you get is suitable for your board finally where the option is available obtain dual channel performance by fitting identical pairs of RAM modules according to the color coding of your RAM slots and the instructions in your motherboard manual back in the early 1980s the first computer that I owned and programmed was this one a Sinclair zx81 and this has got one kilobyte of RAM and given that modern computers have gigabytes of RAM this means that modern computers have over a million times more RAM than the first machine I ever used in program and that I find absolutely extraordinary and it makes me speculate on the fact that the chances are that many of you watching this video right now will end up owning computers that have got terabytes and even petabytes of RAM and we can only imagine what that amount of RAM will actually be used for in the future but now that's it for another video if you enjoy what you see there please pass out the like button if you haven't subscribed please subscribe and I hope to talk to you again very soon [Music] you

Channel: ExplainingComputers

Views: 146,166

Keywords: RAM, PC RAM, computer RAM, computer memory, random access memory, RAM history, history of RAM, non-volatile storage, volatile storage, magnetic core storage, core storage, SIP, SIMM, DIMM, SO-DIMM, SODIMM, laptop memory, PC memory, DDR, SRAM, DRAM, SDRAM, DDR2, DDR3, DDR4, DDR5, RAM specifications, choosing RAM, RAM speed, DDR3 speed, DDR4 speed, Christopher Barnatt, Barnatt

Id: qmJWkfOTOPg

Length: 12min 59sec (779 seconds)

Published: Sun Dec 09 2018