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geekhack Community => Other Geeky Stuff => Topic started by: y11971alex on Sat, 23 January 2016, 00:21:15

Title: HDD is Random Access
Post by: y11971alex on Sat, 23 January 2016, 00:21:15

So... I've been taught in elementary school technology class that HDD is a form of RAM, but it isn't the "main memory" component of most PCs, and main memory is defined as the default location from which the CPU directly accesses information.

The reasoning that goes into this is that HDDs provide random access to its data.  And it stores information, so it's "memory". 

And now some people are telling me that HDDs aren't random access memory.

Any comments?

Title: Re: HDD is Random Access
Post by: FLFisherman on Sat, 23 January 2016, 00:27:25

A HDD is a hard disk drive. I think what's troubling you are definitions.

Hard drives can read data using random access. That means data doesn't have to retrieved in any specific order. For example:

1, 2, 3, 4, 5

With random access we can pull out 2, 4, 5, 1, or 2 in any order we want. If we didn't have random access we would have to pull the numbers in an order, like 1, 2, 3, 4, 5 or 5, 4, 3, 2, 1.

I think you're right in saying it's not the "main memory" of most PCs. That would be the CPU. Again, it really comes down to which definitions you're using. If you're using the exact, technical definitions then everything you say (except And now some people are telling me that HDDs aren't random access memory.) is correct.

It's 1:30 AM though and I've got to wake up early so I can't go further into this. Someone else please add on (or correct me!) if possible.

Title: Re: HDD is Random Access
Post by: rowdy on Sat, 23 January 2016, 00:45:36

The "random access" part is in contradistinction to, say, tapes, which were sequential access.  To read a point half way through a tape, you'd have to read the entire tape from the start until you found the part you were looking for.

Hard drives are random access as you can access any part of the drive immediately without having to read from the beginning of the drive (although directory schemes will usually require several reads to determine exactly where the information is stored on the drive, unless we are talking about direct access).

In generic terms hard drives are sometimes called "memory" or "permanent memory" as the computer can store programs and data on them and it will not disappear when the power is turned off.

Hard drives can be used to store the instructions from a program that is running, but for performance reasons it is usually moved back into the main memory first before being executed.  This is more usually called "swap space", as when the computer's main memory is full of running programs it will swap some of those to the hard drive and swap previously stored applications back in to main memory.

Title: Re: HDD is Random Access
Post by: Vadisi on Sat, 23 January 2016, 04:43:28

Wow, the amount of misinformation out there, storage is not RAM. Here is a diagram that I made in paint (all the best diagrams are made in paint).
(http://i.imgur.com/bAlErih.jpg)
It's WAY more technical that this but hopefully it will help you understand

Title: Re: HDD is Random Access
Post by: pr0ximity on Sat, 23 January 2016, 05:32:39

Quote from: Vadisi on Sat, 23 January 2016, 04:43:28

Wow, the amount of misinformation out there, storage is not RAM. Here is a diagram that I made in paint (all the best diagrams are made in paint).

Show Image

(http://i.imgur.com/bAlErih.jpg)

It's WAY more technical that this but hopefully it will help you understand

That's very black-and-white and not why the OP is confused with terminology.

What do you call a RAM-disk?

Title: Re: HDD is Random Access
Post by: fanpeople on Sat, 23 January 2016, 06:12:12

Quote from: Vadisi on Sat, 23 January 2016, 04:43:28

Wow, the amount of misinformation out there, storage is not RAM. Here is a diagram that I made in paint (all the best diagrams are made in paint).

Show Image

(http://i.imgur.com/bAlErih.jpg)

It's WAY more technical that this but hopefully it will help you understand

Saved for future use as a work meeting arrousal.

Title: Re: HDD is Random Access
Post by: baldgye on Sat, 23 January 2016, 06:14:51

Quote from: pr0ximity on Sat, 23 January 2016, 05:32:39

What do you call a RAM-disk?

(http://i.imgur.com/E9K6yhq.jpg)

Title: Re: HDD is Random Access
Post by: pr0ximity on Sat, 23 January 2016, 07:35:06

Quote from: baldgye on Sat, 23 January 2016, 06:14:51

Quote from: pr0ximity on Sat, 23 January 2016, 05:32:39

What do you call a RAM-disk?

Show Image

(http://i.imgur.com/E9K6yhq.jpg)

Touché

Title: Re: HDD is Random Access
Post by: y11971alex on Sat, 23 January 2016, 11:04:03

Quote from: Vadisi on Sat, 23 January 2016, 04:43:28

Wow, the amount of misinformation out there, storage is not RAM. Here is a diagram that I made in paint (all the best diagrams are made in paint).

Show Image

(http://i.imgur.com/bAlErih.jpg)

It's WAY more technical that this but hopefully it will help you understand

(http://www.columbia.edu/cu/computinghistory/core3.jpg)

I personally think (as well as people who taught me) that HDD is a memory device that provides random access, and thus can be called "random access memory" (RAM). They may not be SDRAM, but they are RAM nonetheless.

And after some trawling on the Internet, the original HDD was part of a "Random Access Method of Accounting..." RAMAC from IBM.  If that "Random Access" part doesn't refer to the HDD, which is the selling point of this computer, then I don't know what it means.

(http://s7.computerhistory.org/is/image/CHM/500004431-03-01?$re-zoomed$)

Title: Re: HDD is Random Access
Post by: Leslieann on Sat, 23 January 2016, 15:41:15

A hard disk is a form of RAM, as it is Random Accessed Memory, as is tape. You can access it, I.E. read or write to it. It has nothing to do with stop, start, or anything.

The alternative to RAM is ROM, Read Only Memory, which usually requires a special tool to write to it and has a much shorter lifespan for writes. This is what your Bios is stored in as well as CD-ROM, DVD-ROM.  Some may remember DVD-RAM, that allowed to write more than one time to it, which also means a DVD-RW is also RAM (notice the lack of ROM in the name).

All of you would fail the old A+ certification section on ROM vs RAM (not sure about the new one).


As for drives versus memory, we call them different because it's just easier in common language to do so (just as people used to call the computer tower the CPU).
The difference is the volatility, what we consider RAM is volatile, meaning when it loses power, it loses the information. Non-Volatile is an SSD or hard disk, they retain memory in the event of a power loss. Both are still RAM. We use two different sources because non-volatile has always been slower than volatile, however both can and are used for the exact same function, storage/swapping of data. Your own computer uses the hard disk as "ram" when the "ram" is full, Linux calls it a swap file, Microsoft calls it virtual memory, both are the opposite of using your "ram" as a hard disk, which is called a RAM drive.