what's the right amount of RAM for a road warrior?
Nov 8, 2007, 8:00 pm
#31
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The "system cache" number in Task Manager represents the amount of physical memory in use, including that used by programs and the file cache. At the moment, my task manager shows about 800MB in use and a system cache of 816MB; "Available" is listed as 1.2GB, so clearly the cache isn't in addition to memory used by programs.
I have 1G of physical RAM, plus a 1.4G swap file, i.e. a total of 2419M virtual memory. "Commit Charge" shows up as 616M. This is the memory used by programs. System cache is now at 420M, and available at 262M. So, of my 1G physical memory, 420M are taken for file cache, 262M are available and 1024-420-262=342M are used by programs. 616M-342M=274M are swapped to the HD.
If you have Linux, install htop. It shows you all that very nicely.
SmilingBoy.
Edit: Here's a good explanation: http://www.codinghorror.com/blog/archives/000393.html
Last edited by SmilingBoy; Nov 8, 2007 at 8:11 pm
Nov 8, 2007, 8:05 pm
#32
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A lot of people thing there's "single-channel" and "dual-channel" memory - but there's not.
Nov 8, 2007, 8:52 pm
#33
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Uh, sorry, this is just not true. If you have 2GB of RAM and are using only 1GB, the other 1GB is indeed sitting there idle.
You seem to be thinking of disk caching, which means that the first time you access a file on disk, it is loaded into a cache in RAM (most recently access parts of it, anyway) and any subsequent accesses to the same piece of the file get read quickly from the cache and not from the disk again. But, hard disks themselves have a cache built-in. Computer operating systems may do some disk caching but must reserve RAM for that, and the amount reserved is pretty limited. A hard disk will have a cache of only 8MB or 16MB at most. Not much RAM on your computer's hard disk is reserved for a cache.
You seem to be thinking of disk caching, which means that the first time you access a file on disk, it is loaded into a cache in RAM (most recently access parts of it, anyway) and any subsequent accesses to the same piece of the file get read quickly from the cache and not from the disk again. But, hard disks themselves have a cache built-in. Computer operating systems may do some disk caching but must reserve RAM for that, and the amount reserved is pretty limited. A hard disk will have a cache of only 8MB or 16MB at most. Not much RAM on your computer's hard disk is reserved for a cache.
Nov 8, 2007, 9:40 pm
#34
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Nov 9, 2007, 2:43 am
#35
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A hard disk will have a cache of only 8MB or 16MB at most. Not much RAM on your computer's hard disk is reserved for a cache.
The cache file wouldn't be any bigger, because it's based on the applications I have open, not on available RAM.
Linux and most other operating systems *will* just fill up extra memory with file system caches, and that can have a *big* impact on disk drive use. Caching on reads is free if you have the memory to spare, and speculative read-ahead is part of modern file system design.
I'm fairly sure though, that Windows isn't nearly that dumb.
But you wouldn't even notice the difference - except for more disk space required to hibernate, more time to hibernate and resume.
Yes it is; it's a mode of operation for the motherboard... dual channel or single channel mode (or potentially quad-channel, on the new Xeon boards), depending on the memory configuration.
it's a way of designing a motherboard so the latencies inherent in memory gating circuitry in one module overlap with data transfer in the other.
Dual channel reads (or writes) are simultaneous, and have no impact on latency - rather, they have an impact on bandwidth. Dual channel means, essentially, that memory is being read in a 128-bit chunk at a time (a pair of DIMMs) rather than in 64-bit chunks (a single DIMM wide.)
And DC only increases memory bandwidth by a few percent anyway.
Which, depending on the generation of the processor/motherboad, may or may not make a huge difference in overall system speed... for the Pentium 4, this was a very big deal, as the front side bus of the processors out at the time was twice the speed of the first-generation DDR memory, and so in order to match the FSB, dual channel made a HUGE difference.
With current laptops and faster-clocked DDR2 memory, the difference is not nearly as big, but it's still significant.
If I had one 1gb module in my laptop, I'd double it by buying another just like it (DC only works if the chip electronics in the two sticks are well-matched), not scrapping the 1gb to put in a 2gb.
A lot of people thing there's "single-channel" and "dual-channel" memory - but there's not.
A lot of people thing there's "single-channel" and "dual-channel" memory - but there's not.
Nov 9, 2007, 5:53 am
#36
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Can any of you tell me what in the world you would need 3GB of RAM for on a basic laptop?? Seriously. I have 2GB on my Dell XP laptop, but I almost never use more than 1GB, and that's only when I'm editing photos. If you aren't, you really don't need much RAM. 3GB is way overkill for someone using XP, unless you do heavy photo or video editing or have some specific software that really uses that RAM. Vista is more of a memory hog than XP, that's why I recommend 2GB for it.
Can any of you tell me right now how much RAM you are using at this moment? I have 9 Firefox windows open and a photo editor and I'm using 720MB out of my 2GB. I've never come close to using it all. Even so, running a little over is not the end of the world - it just means you swap some RAM out to hard disk.
Can any of you tell me right now how much RAM you are using at this moment? I have 9 Firefox windows open and a photo editor and I'm using 720MB out of my 2GB. I've never come close to using it all. Even so, running a little over is not the end of the world - it just means you swap some RAM out to hard disk.
My current laptop is an IBM/Lenovo T60 with 2GB of RAM and a 2.33GHz C2D. I've occasionally felt the need for more RAM.
Nov 9, 2007, 6:05 am
#37
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I do systems integration work in healthcare, and have to support multiple versions of applications and operating environments. I run Windows XP as my host operating system, and use VMWare with Win2K and Linux guests to maintain my discrete work environments (saves a lot of hassle when upgrading laptops, too). I commonly have close to 2GB in use, with common office applications running in the host operating system and 2-3 virtual machines running for my integration work environments.
My current laptop is an IBM/Lenovo T60 with 2GB of RAM and a 2.33GHz C2D. I've occasionally felt the need for more RAM.
My current laptop is an IBM/Lenovo T60 with 2GB of RAM and a 2.33GHz C2D. I've occasionally felt the need for more RAM.
SmilingBoy.
Nov 9, 2007, 9:14 am
#38
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No, that's interleaved memory, which is a separate issue.
Dual channel reads (or writes) are simultaneous, and have no impact on latency - rather, they have an impact on bandwidth. Dual channel means, essentially, that memory is being read in a 128-bit chunk at a time (a pair of DIMMs) rather than in 64-bit chunks (a single DIMM wide.)
Dual channel reads (or writes) are simultaneous, and have no impact on latency - rather, they have an impact on bandwidth. Dual channel means, essentially, that memory is being read in a 128-bit chunk at a time (a pair of DIMMs) rather than in 64-bit chunks (a single DIMM wide.)
The terminology "dual-channel memory" is being misused by some in the memory industry, which can mislead the consumer. The fact is there's no such thing as dual-channel memory. There are, however, dual-channel platforms.
When properly used, the term "dual channel" refers to the DDR or DDR2 chipset on certain motherboards designed with two memory channels instead of one. The two channels handle memory-processing more efficiently by utilizing the theoretical bandwidth of the two modules, thus reducing system latencies, the timing delays that inherently occur with one memory module. For example, one controller reads and writes data while the second controller prepares for the next access, hence, eliminating the reset and setup delays that occur before one memory module can begin the read/write process all over again. Think of it like two relay runners. The first runner runs one leg while the second runner sets up and prepares to receive the baton smoothly and carry on the task at hand without delay. While performance gains from dual-channel chipsets aren't huge, they can increase bandwidth by as much as 10 percent. To those seeking to push the performance envelope, that 10 percent can be very important.
When properly used, the term "dual channel" refers to the DDR or DDR2 chipset on certain motherboards designed with two memory channels instead of one. The two channels handle memory-processing more efficiently by utilizing the theoretical bandwidth of the two modules, thus reducing system latencies, the timing delays that inherently occur with one memory module. For example, one controller reads and writes data while the second controller prepares for the next access, hence, eliminating the reset and setup delays that occur before one memory module can begin the read/write process all over again. Think of it like two relay runners. The first runner runs one leg while the second runner sets up and prepares to receive the baton smoothly and carry on the task at hand without delay. While performance gains from dual-channel chipsets aren't huge, they can increase bandwidth by as much as 10 percent. To those seeking to push the performance envelope, that 10 percent can be very important.
Nov 9, 2007, 9:36 am
#39
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No one has suggested that there is such a thing as "dual channel memory".
Dual channel "whatever" is a function of the motherboard using, in multiples of two, identically spec'd RAM modules.
Though it is not an exact analogy RAM running in dual channel mode is somewhat like stipping a pair of hard drives.
I don't quite see what the hang up is on this issue is. Dual channel mode mobos is just where commercially available/affordable state-of-the-art is right now.
Nov 9, 2007, 10:00 am
#40
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Running the memory controller in dual channel mode effectively doubles the memory bandwidth. It runs 128 bit memory accesses instead of running a single 64-bit memory channel. It accesses 64-bits from each DIMM in the dual-channel configuration at the same time, instead of only being able to access one 64-bit read/write at a time (in the same clock cycles). So, if you look at the path to memory as a pipe, in dual-channel mode, the pipe is twice as thick. Even better, there are two pipes operating at the same time as one pipe of the same width in single channel mode.
-David
Last edited by LIH Prem; Nov 9, 2007 at 10:09 am
Nov 9, 2007, 10:01 am
#41
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Nov 9, 2007, 10:28 am
#42
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Running the memory controller in dual channel mode effectively doubles the memory bandwidth. It runs 128 bit memory accesses instead of running a single 64-bit memory channel. It accesses 64-bits from each DIMM in the dual-channel configuration at the same time, instead of only being able to access one 64-bit read/write at a time (in the same clock cycles). So, if you look at the path to memory as a pipe, in dual-channel mode, the pipe is twice as thick. Even better, there are two pipes operating at the same time as one pipe of the same width in single channel mode.
Tom's Hardware found no significant difference between single-channel and dual-channel configurations in synthetic and game benchmarks.[2] Generally speaking, dual channel configuration is a very minor upgrade, and without other system tweaks, the difference may not even be noticeable. While there is no reason not to use dual-channel over single-channel, where all other things are equal, the question often comes up whether it is advisable to add additional RAM if doing so will break dual-channel compatibility. Having more total RAM available is generally more beneficial than maintaining dual-channel configuration.
Nov 9, 2007, 11:12 am
#43
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Modern operating systems allocate RAM dynamically; there's no need for static allocation for cache. Old MacOS versions did, as did DOS ("Smartdrv") and Windows 3.x... all of which are dead obsolete now.
The hard drive's internal cache is separate from the caching done by the operating system (and indeed, the HD is unaware of the operating system's caching, and the OS is largely unaware of the HD's caching.)
...
If so, Windows is even dumber than I thought...
Linux and most other operating systems *will* just fill up extra memory with file system caches, and that can have a *big* impact on disk drive use. Caching on reads is free if you have the memory to spare, and speculative read-ahead is part of modern file system design.
I'm fairly sure though, that Windows isn't nearly that dumb.
The hard drive's internal cache is separate from the caching done by the operating system (and indeed, the HD is unaware of the operating system's caching, and the OS is largely unaware of the HD's caching.)
...
If so, Windows is even dumber than I thought...
Linux and most other operating systems *will* just fill up extra memory with file system caches, and that can have a *big* impact on disk drive use. Caching on reads is free if you have the memory to spare, and speculative read-ahead is part of modern file system design.
I'm fairly sure though, that Windows isn't nearly that dumb.
Maybe not for you, but as you can read from this thread, it's very useful for a number of us. I use hibernate every day. I also use standby when I'm only going to have the computer off for brief periods.
Nov 9, 2007, 11:15 am
#44
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I've seen the speed difference between the data being in memory and having to pull it in off the disk. The largest cache I've seen on a drive is 16mb. I've watched things zoom by on multi-hundred-megabyte chunks of data because it was in memory. The cache on the drive isn't going to give that speed on something that big.
Nov 9, 2007, 12:02 pm
#45
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Great - but that's irrelevant here, since Windows XP (for clients, anyway) is designed to work better with a smaller file/application cache and does not use up all your unavailable RAM for a big system cache unless you ignore Microsoft's advice and enable the system cache. I don't know why XP doesn't work well with the System Cache - ask Microsoft. My point stands: unless you are running out of RAM and have a real need for it, buying way more than you need is just a waste of money.
SmilingBoy.